**Polyimides Bearing Long-Chain Alkyl Groups and Their Application for Liquid Crystal Alignment Layer and Printed Electronics**

Yusuke Tsuda *Kurume National College of Technology Japan* 

## **1. Introduction**

Polyimides exhibit excellent thermal and mechanical properties, and have extensive engineering and microelectronics applications. Aromatic polyimides such as polyimides based on pyromellitic dianhydride are prepared from aromatic diamines and aromatic tetracarboxylic dianhydrides *via* poly(amic acid)s. Since conventional aromatic polyimides are insoluble, these polymers are usually processed as the corresponding soluble poly(amic acid) precursors, and then either thermally or chemically imidized. However, owing to the instability of poly(amic acid)s and the liberation of water in the imidization process, problems can arise (Fig. 1). Extensive research has been carried out to improve the solubility of polyimides and successful recent examples involve the incorporation of fluorine moieties, isomeric moieties, methylene units, triaryl imidazole pendant groups, spiro linkage groups, and sulfonated structure. Soluble polyimides bearing long-chain alkyl groups have also been reported, and their applications mainly involve their use as alignment layers for liquid crystal displays (LCDs).

Our research group has systematically investigated the synthesis and characterization of soluble polyimides based on aromatic diamines bearing long-chain alkyl groups such as alkyldiaminobenzophenone (ADBP-X, X = carbon numbers of alkyl chain) (Tsuda et al., 2000a) alkoxydiaminobenzene (AODB-X) (Tsuda et al., 2000b), diaminobenzoic acid alkylester (DBAE-X) (Tsuda et al., 2006), and alkyldiaminobenzamide (ADBA-X) (Tsuda et al., 2008), and the results from these research are described in the original papers and the review paper (Tsuda, 2009). Our recent paper has described soluble polyimides having dendritic moieties on their side chain, and it was found that these polyimides having dendritic side chains were applicable for the vertically aligned nematic liquid crystal displays (VAN-LCDs) (Tsuda et al., 2009). These dendronized polyimides were synthesized using the novel diamine monomer having a first-generation monodendron, 3,4,5-tris(ndodecyloxy)benzoate and the monomer having a second-generation monodendron, 3,4,5 tris[-3',4',5'-tri(n-dodecyloxy)benzyloxy]benzoate.

Some soluble polyimides were synthesized from the diamine monomer having three longchain alkyl groups; aliphatic tetracarboxylic dianhydride; 5-(2,5-dioxotetrahydrofuryl)-3 methyl-3-cyclohexene-1,2-dicarboxylic anhydride (Cyclohexene-DA) or aromatic tetracarboxylic dianhydride; 3,3',4,4'-diphenylsulfone tetracarboxylic dianhydride (DSDA)

Polyimides Bearing Long-Chain Alkyl Groups and

O

O

O

x y

O

H2N NH2

AODB-X (X=10~14)

R

O CXH2X+1

C O O O

BTDA

(x + y) <sup>+</sup> <sup>x</sup>

C O N N

> C O N

H2N NH2

DPABA-12

H

OC10H21 C10H21O OC10H21 C O O

O C H2N NH2 3C10-PEPEDA

O

OC12H23 C12H23O OC12H23

CXH2X+1

O

O

O

O

H2N NH2

C O

ADBP-X (X=9~14)

Their Application for Liquid Crystal Alignment Layer and Printed Electronics 5

y

C O O

H2N NH2

OC12H23 C12H23O OC12H23

<sup>C</sup> <sup>O</sup> <sup>O</sup> CXH2X+1 DBAE-X (X=8~14)

NH C O H2N NH2

12G1-AG-Terphenyldiamine

OC10H21 C10H21O OC10H21 C O O

> N C O H2N NH2

3C10-PEPADA

Fig. 2. Soluble polyimides bearing long-chain alkyl groups

H

H2N NH2

R

H2N O NH2

DDE

O

O

OC10H21 C10H21O OC10H21 C O N

> N C O H2N NH2

3C10-PAPADA

alkylbenzophenone was performed by catalytic hydrogenation using palladium on carbon and hydrogen gas introduced by 3-5 L gas-bag. Although hydrazine hydrate/ethanol system is sometimes used for the reduction of nitro compounds, this system is not preferred because the carbonyl group in 3,5-dinitro-4'-alkylbenzophenones reacts with hydrazine. Alkyloxydiaminobenzenes (AODB-10~14) were prepared in two steps using 2,4 dinitrophenol as the starting material. The Williamson reaction using 2,4-dinitrophenol and 1-bromoalkanes catalyzed by potassium carbonate in DMAc gave 1-alkyloxy-2,4 dinitrobenzenes in satisfactory yields. The reduction of 1-alkyloxy-2,4-dinitrobenzenes was performed by catalytic hydrogenation using Pd/C and hydrogen gas at 0.2-0.3 Mpa.

H

H

C O N N

H2N NH2

<sup>C</sup> <sup>O</sup> <sup>N</sup> <sup>H</sup> CXH2X+1

ADBA-X

O

O

n n

(X=9~14) <sup>O</sup>

C12H23O C12H23O C12H23O

O

O O C O O

OC12H23 C12H23O OC12H23

> OC12H23 OC12H23 OC12H23

NH C O H2N NH2

12G2-AG-Terpnenyldiamine

O

Cyclohexene-DA

O

O O

O

<sup>S</sup> <sup>O</sup> <sup>O</sup> O O

CH3

O O

O

DSDA

O

3,4'-ODPA

O

O O

O

O

<sup>O</sup> <sup>O</sup> O

2) Ac2O, Pyridine 120oC, 4h, in NMP

1) r. t, 12h, in NMP

Fig. 1. Conventional polyimides and soluble polyimides

or 3,4'-oxydiphthalic anhydride (3,4'-ODPA) as a dianhydride, and 4,4' diaminodiphenylether (DDE) as a diamine co-monomer. Thin films of the obtained polyimides were irradiated by UV light (λmax; 254 nm) , and the contact angles for the water decreased from near 100° (hydrophobicity) to near 20° (hydrophilicity) in proportion to the irradiated UV light energy. Thus, the surface wettability of polyimides bearing longchain alkyl groups can be controlled by UV light irradiation, such methods are expected to be applied in the field of organic, flexible and printed electronics (Tsuda et al., 2010, 2011a, 2011b).

In this chapter, the author reviews the synthesis and basic properties of soluble polyimides bearing long-chain alkyl groups, and their application for liquid crystal alignment layer and printed electronics.

## **2. Results and discussion**

In this section, the synthesis of aromatic diamine monomers having long-chain alkyl groups and corresponding soluble polyimides bearing long-chain alkyl group (Fig. 2), their basic polymer properties, and the application for VAN-LCDs and printed electronics are described.

### **2.1 Synthesis of aromatic diamine monomers containing long-chain alkyl groups**

The synthesis routes for aromatic diamines bearing single long-chain alkyl groups are illustrated in Fig. 3. Alkyldiaminobenzophenones (ADBP-9~14) were prepared *via* two steps using 3,5-dinitrobenzoyl chloride as the starting material. The Friedel-Crafts reaction of 3,5 dinitrobenzoyl chloride with alkylbenzene catalyzed by aluminum chloride in nitrobenzene gave 3,5-dinitro-4'-alkylbenzophenones in good yields. The reduction of 3,5-dinitro-4'-

or 3,4'-oxydiphthalic anhydride (3,4'-ODPA) as a dianhydride, and 4,4' diaminodiphenylether (DDE) as a diamine co-monomer. Thin films of the obtained polyimides were irradiated by UV light (λmax; 254 nm) , and the contact angles for the water decreased from near 100° (hydrophobicity) to near 20° (hydrophilicity) in proportion to the irradiated UV light energy. Thus, the surface wettability of polyimides bearing longchain alkyl groups can be controlled by UV light irradiation, such methods are expected to be applied in the field of organic, flexible and printed electronics (Tsuda et al., 2010, 2011a,

In this chapter, the author reviews the synthesis and basic properties of soluble polyimides bearing long-chain alkyl groups, and their application for liquid crystal alignment layer and

In this section, the synthesis of aromatic diamine monomers having long-chain alkyl groups and corresponding soluble polyimides bearing long-chain alkyl group (Fig. 2), their basic polymer properties, and the application for VAN-LCDs and printed electronics are

**2.1 Synthesis of aromatic diamine monomers containing long-chain alkyl groups**  The synthesis routes for aromatic diamines bearing single long-chain alkyl groups are illustrated in Fig. 3. Alkyldiaminobenzophenones (ADBP-9~14) were prepared *via* two steps using 3,5-dinitrobenzoyl chloride as the starting material. The Friedel-Crafts reaction of 3,5 dinitrobenzoyl chloride with alkylbenzene catalyzed by aluminum chloride in nitrobenzene gave 3,5-dinitro-4'-alkylbenzophenones in good yields. The reduction of 3,5-dinitro-4'-

Fig. 1. Conventional polyimides and soluble polyimides

2011b).

described.

printed electronics.

**2. Results and discussion** 

Fig. 2. Soluble polyimides bearing long-chain alkyl groups

alkylbenzophenone was performed by catalytic hydrogenation using palladium on carbon and hydrogen gas introduced by 3-5 L gas-bag. Although hydrazine hydrate/ethanol system is sometimes used for the reduction of nitro compounds, this system is not preferred because the carbonyl group in 3,5-dinitro-4'-alkylbenzophenones reacts with hydrazine.

Alkyloxydiaminobenzenes (AODB-10~14) were prepared in two steps using 2,4 dinitrophenol as the starting material. The Williamson reaction using 2,4-dinitrophenol and 1-bromoalkanes catalyzed by potassium carbonate in DMAc gave 1-alkyloxy-2,4 dinitrobenzenes in satisfactory yields. The reduction of 1-alkyloxy-2,4-dinitrobenzenes was performed by catalytic hydrogenation using Pd/C and hydrogen gas at 0.2-0.3 Mpa.

Polyimides Bearing Long-Chain Alkyl Groups and

Their Application for Liquid Crystal Alignment Layer and Printed Electronics 7

Fig. 4. Synthesis of aromatic diamines having triple long-chain alkyl groups

precursor of DPABA, and this was finally hydrogenated to DPABA.

**2.2 Synthesis of soluble polyimides bearing long-chain alkyl groups** 

reported elsewhere.

following the method shown in Fig. 4. 3,4,5-Trialkyloxybenzoyl chloride, known as the building block for Percec-type dendrons, was synthesized from 3,4,5-trihydroxybenzoic acid methyl ester (gallic acid methyl ester) followed by Williamson-etherification using alkylbromide catalyzed by potassium carbonate, hydrolysis of ester groups by potassium hydroxide, then acid chlorination using thionyl chloride. The condensation reaction using the above acid chloride and 3,5-dinitroaniline catalyzed by triethylamine gave the dinitro-

4-[3,5-Bis(3-aminophenyl)phenyl]carbonylamino]phenyl 3,4,5-tris (n-dodecyloxy)benzyloxy benzoate (12G1-AG-Terphenyldiamine) and 4-[3,5-Bis (3-aminophenyl) phenyl] carbonylamino] phenyl 3,4,5-tris[3',4',5'-tris(n-dodecyloxy) benzyloxy] benzoate (12G2-AG-Terphenyl diamine) were synthesized by the method shown in Fig. 5 using the first- and second- generation Percec-type monodendrons. These synthesis routes include the condensation reactions with 3,5-dibromo benzoic acid and 3',4',5'-tris (ndodecyloxy)benzyloxy chloride with 4-aminophenol, followed by Suzuki coupling reaction with 3-aminophenyl boronic acid. It is considered that these synthetic methods of aromatic diamine monomers using Suzuki coupling are the versatile method as the synthesis of aromatic diamines without the severe reduction that sometime causes the side reaction. Novel diamine monomers, such as 3C10-PEPEDA, 3C10-PEPADA and 3C10-PAPADA having three long-chain alkyl groups connected by phenylester and/or phenylamide linkages were recently synthesized *via* several step reactions from Gallic acid methyl ester using protect group synthetic technique. The detail description of these monomer syntheses will be

The synthesis route for the polyimides and copolyimides based on BTDA (Cyclohexene-DA, DSDA, 3,4'-ODPA), DDE and aromatic diamines bearing long-chain alkyl groups is illustrated in Fig. 2. Two-step polymerization systems consisting of poly(amic acid)s synthesis and chemical imidization were performed. The poly(amic acid)s were obtained by reacting the mixture of diamines with an equimolar amount of BTDA at room temperature for 12 h under an argon atmosphere. Polyimides were obtained by chemical imidization at 120C in the presence of pyridine as base catalyst and acetic anhydride as dehydrating agent. These are the optimized synthesis conditions previously developed for the synthesis

Fig. 3. Synthesis of aromatic diamines having single long-chain alkyl groups

Although the hydrazine hydrate/ethanol system can be used for the reduction of nitrocompounds, the medium pressure system is preferable due to better yields and purity of the products.

Diaminobenzoic acid alkylesters (DBAE-8~14) were prepared in two steps using 3,5 dinitrobenzoyl chloride as the starting material. The esterification reaction using 3,5 dinitrobenzoyl chloride and aliphatic alcohols having long-chain alkyl groups catalyzed by triethylamine in THF gave alkyl 3,5-dinitrobenzoate in satisfactory yield. The reduction of alkyl 3,5-dinitrobenzoate was performed by catalytic hydrogenation using Pd/C as a catalyst and hydrazine hydrate/ethanol as a hydrogen generator. The relatively mild hydrogenation using hydrazine hydrate/ethanol system seemed to be preferable in the case of alkyl 3,5 dinitrobenzoate, because the scissions of ester linkages were sometimes recognized besides the hydrogenation of nitro-groups in the use of medium pressure hydrogenerator.

Alkyldiaminobenzamides (ADBA-9~14) were prepared in two steps using 3,5 dinitrobenzoyl chloride as the starting material. The condensation reaction using 3,5 dinitrobenzoyl chloride and aliphatic amines having long-chain alkyl groups catalyzed by triethylamine in THF gave N-alkyl-3,5-diaminobenzamides in satisfactory yields. The reduction of N-alkyl-3,5-diaminobenzamide was performed by catalytic hydrogenation using Pd/C and hydrogen gas at 0.2-0.3 MPa in a medium pressure hydrogenerator in satisfactory yield (60-80%).

The aromatic diamines containing first-generation dendritic moieties, N-(3,5 diaminophenyl)-3,4,5-tris(alkoxy)benzamide (DPABA-X, X=6,12), were synthesized Polyimides Bearing Long-Chain Alkyl Groups and Their Application for Liquid Crystal Alignment Layer and Printed Electronics 7

6 Features of Liquid Crystal Display Materials and Processes

H2, Pd/C DMF 80°C, 24h

> H2, Pd/C DMF 80°C, 24h 0.2-0.3 MPa

NH2NH2, Pd/C

Ethanol, reflux, 12h

H2 , Pd/C

EtOH/THF, r. t, 12h 0.2-0.3 MPa

CXH2X+1 <sup>O</sup> <sup>N</sup>

H2N NH2

C O

ADBP-X (X=9~14) CxH2x+1

OCxH2x+1

H2N NH2

DBAE-9-branch-A

R =

R =

H2N NH2

H

ADBA-X(X=9~14)

DBAE-9-branch-B

CXH2X+1

O OR

AODB-X (X=10~14)

DBAE-8~14 (R = n-C8H17 ~ n-C14H29)

H2N NH2

CxH2x+1

OCxH2x+1

O2N NO2

C O

X=9~14

O2N NO2

O2N NO2

O OR

O2N NO2

O N H

Although the hydrazine hydrate/ethanol system can be used for the reduction of nitrocompounds, the medium pressure system is preferable due to better yields and purity of the

Diaminobenzoic acid alkylesters (DBAE-8~14) were prepared in two steps using 3,5 dinitrobenzoyl chloride as the starting material. The esterification reaction using 3,5 dinitrobenzoyl chloride and aliphatic alcohols having long-chain alkyl groups catalyzed by triethylamine in THF gave alkyl 3,5-dinitrobenzoate in satisfactory yield. The reduction of alkyl 3,5-dinitrobenzoate was performed by catalytic hydrogenation using Pd/C as a catalyst and hydrazine hydrate/ethanol as a hydrogen generator. The relatively mild hydrogenation using hydrazine hydrate/ethanol system seemed to be preferable in the case of alkyl 3,5 dinitrobenzoate, because the scissions of ester linkages were sometimes recognized besides the

Alkyldiaminobenzamides (ADBA-9~14) were prepared in two steps using 3,5 dinitrobenzoyl chloride as the starting material. The condensation reaction using 3,5 dinitrobenzoyl chloride and aliphatic amines having long-chain alkyl groups catalyzed by triethylamine in THF gave N-alkyl-3,5-diaminobenzamides in satisfactory yields. The reduction of N-alkyl-3,5-diaminobenzamide was performed by catalytic hydrogenation using Pd/C and hydrogen gas at 0.2-0.3 MPa in a medium pressure hydrogenerator in

The aromatic diamines containing first-generation dendritic moieties, N-(3,5 diaminophenyl)-3,4,5-tris(alkoxy)benzamide (DPABA-X, X=6,12), were synthesized

Nitrobenzene 100°C, 3h

> DMAc 120°C, 24h

Triethylamine THF, r. t, 3h

THF, r. t, 3h

Fig. 3. Synthesis of aromatic diamines having single long-chain alkyl groups

hydrogenation of nitro-groups in the use of medium pressure hydrogenerator.

Triethylamine

K2CO3

AlCl3

O2N NO2

C

O2N NO2

O2N NO2

O Cl

O2N NO2

O Cl

products.

<sup>O</sup> Cl CxH2x+1

+

CxH2x+1Br

R-OH

CXH2X+1NH2

OH

+

+

satisfactory yield (60-80%).

+

Fig. 4. Synthesis of aromatic diamines having triple long-chain alkyl groups

following the method shown in Fig. 4. 3,4,5-Trialkyloxybenzoyl chloride, known as the building block for Percec-type dendrons, was synthesized from 3,4,5-trihydroxybenzoic acid methyl ester (gallic acid methyl ester) followed by Williamson-etherification using alkylbromide catalyzed by potassium carbonate, hydrolysis of ester groups by potassium hydroxide, then acid chlorination using thionyl chloride. The condensation reaction using the above acid chloride and 3,5-dinitroaniline catalyzed by triethylamine gave the dinitroprecursor of DPABA, and this was finally hydrogenated to DPABA.

4-[3,5-Bis(3-aminophenyl)phenyl]carbonylamino]phenyl 3,4,5-tris (n-dodecyloxy)benzyloxy benzoate (12G1-AG-Terphenyldiamine) and 4-[3,5-Bis (3-aminophenyl) phenyl] carbonylamino] phenyl 3,4,5-tris[3',4',5'-tris(n-dodecyloxy) benzyloxy] benzoate (12G2-AG-Terphenyl diamine) were synthesized by the method shown in Fig. 5 using the first- and second- generation Percec-type monodendrons. These synthesis routes include the condensation reactions with 3,5-dibromo benzoic acid and 3',4',5'-tris (ndodecyloxy)benzyloxy chloride with 4-aminophenol, followed by Suzuki coupling reaction with 3-aminophenyl boronic acid. It is considered that these synthetic methods of aromatic diamine monomers using Suzuki coupling are the versatile method as the synthesis of aromatic diamines without the severe reduction that sometime causes the side reaction.

Novel diamine monomers, such as 3C10-PEPEDA, 3C10-PEPADA and 3C10-PAPADA having three long-chain alkyl groups connected by phenylester and/or phenylamide linkages were recently synthesized *via* several step reactions from Gallic acid methyl ester using protect group synthetic technique. The detail description of these monomer syntheses will be reported elsewhere.

#### **2.2 Synthesis of soluble polyimides bearing long-chain alkyl groups**

The synthesis route for the polyimides and copolyimides based on BTDA (Cyclohexene-DA, DSDA, 3,4'-ODPA), DDE and aromatic diamines bearing long-chain alkyl groups is illustrated in Fig. 2. Two-step polymerization systems consisting of poly(amic acid)s synthesis and chemical imidization were performed. The poly(amic acid)s were obtained by reacting the mixture of diamines with an equimolar amount of BTDA at room temperature for 12 h under an argon atmosphere. Polyimides were obtained by chemical imidization at 120C in the presence of pyridine as base catalyst and acetic anhydride as dehydrating agent. These are the optimized synthesis conditions previously developed for the synthesis

Polyimides Bearing Long-Chain Alkyl Groups and

**2.3.1 Solubility** 

ADBP.

Their Application for Liquid Crystal Alignment Layer and Printed Electronics 9

As far as the solublity of polyimides based on long-chain alkyl groups is concerned, the following interesting results have been obtained. Experimental results of homopolymerization and copolymerization based on BTDA/ADBP-12, AODB-12, DBAE-12, ADBA-12, DPABA-12/DDE are summarized in Table 1. Although all polyamic(acid)s were soluble in NMP which is a solvent used for polymerization, however, the solubility of homopolyimides and copolyimides depended on polymer structures. BTDA/ADBP-12 homopolyimides and BTDA/ADBP-12/DDE copolyimides containing 40 mol% of ADBP or more were soluble in NMP. Thus, the effect of long-chain alkyl group in ADBP for the enhancement of solubility was confirmed. BTDA/AODB-12 homopolyimides and BTDA/AODB-12/DDE copolyimides containing 25 mol% or more of AODB-12 units were also soluble in NMP. Judging from the results of copolymerization based on BTDA/ADBP-9~14/DDE and BTDA/AODB-10~14/DDE, it is recognized that AODB bearing alkyl groups *via* an ether linkage were more effective for the enhancement of solubility in comparison to

On the other hand, all homopolyimides and copolyimide based on BTDA/DBAE-8~14/DDE were insoluble in NMP probably due to the rigid ester linkage groups. The experimental results of copolymerization based on BTDA/ADBA-12/DDE are quite unique. Although BTDA/ADBA-12 homopolyimide was insoluble, the copolymers, BTDA/ADBA-12/DDE (100/75/25) and BTDA/ADBA-12/DDE (100/50/50) were soluble in NMP. The solubility of these copolyimides may be improved by the randomizing effect based on copolymerization as well as the entropy effect of long chain linear alkyl groups. Based on the fact that all copolyimides BTDA/DBAE-8~14/DDE were insoluble in NMP, ADBA is more effective for the enhancement of solubility in comparison to DBAE. Fig. 6 summarizes the effect of functional diamines, AODB-X, ADBP-X, ADBA-X and DBAE-X bearing longchain alkyl groups for the enhancement of solubility investigated in our laboratory, and it is concluded that the effect of functional diamines are increased as AODB (ether linkage) > ADBP (benzoyl linkage) > ADBA (amide linkage) > DBAE (ester linkage) (Fig. 6). The polyimides and copolyimides based on BTDA, DPABA-6 or DPABA-12, and DDE containing 50 mol % or more DPABA were soluble, showing that the effect of DPABA for the enhancement of solubility was larger than ADBA. It is speculated that the three long-

Furthermore, several important results concerning on the structure-solubility relationships of the polyimides bearing long-chain alkyl groups are obtained and concluded as follows: (1) ADBP with an even number of carbon atoms were effective in enhancing the solubility, while polymers based on ADBP with an odd number of carbon atoms remained insoluble. It can be assumed that the conformation around C-C bonds of the long-chain alkyl groups and alignment of benzene ring attached with these alkyl groups and carbonyl group affect this odd-even effect. (2) Copolymerization using the conventional aromatic diamine, DDE resulted in the improvement of both the molecular weight and the thermal stability. (3) The copolymerization study based on AODB-10~14 and DDE demonstrated that AODB-12 having 12 methylene units was the most effective in enhancing the solubility. (5) DBAE having branched alkyl chains such as nonan-5-yl 3,5-diaminobenzoate (DBAE-9-branch-A) and 2,6-dimethylheptane-4-yl 3,5-diaminobenzoate (DBAE-9-branch-B) were introduced in these polyimides, and the homopolyimides based on BTDA/ DBAE-9-branch-A and BTDA/ DBAE-9-branch-B, and copolyimides containing more than 50% of DBAE-9-branch-A or DBAE-9-branch-B were soluble in NMP. Thus, it was found that the introduction of

chain alkyl groups in DPABA enhance the solubility of polyimides.

branched alkyl chains enhances solubility.

Fig. 5. Synthesis of aromatic diamines having multiple long-chain alkyl groups (dendritic terphenyl diamines)

of soluble polyimides in our laboratory. BTDA, DSDA and 3,4'-ODPA, these are highly reactive and common aromatic tetracarboxylic dianhydrides were mainly used as a dianhydrides monomer, and DDE that is highly reactive and a common aromatic diamine was used as a diamine co-monomer. In the case of soluble polyimides, clear polyimide solutions were eventually obtained. In other cases, clear poly(amic acid) solutions were obtained, however, gelation or precipitation occurred in the course of imidization process. The polymerizations based on the dendritic diamine monomers, 12G1-AGterphenyldiamine and 12G2-AG-terphenyldiamine were firstly investigated using NMP as a solvent. Although viscous poly(amic acid)s solution were obtained, precipitation sometime occurred during the imidization process. It was speculated that the hydrocarbon and phenyl moiety of dendritic diamine monomers reduces the solubility of polyimides in NMP; therefore, a polar aromatic solvent, *m-*cresol or pyridine were sometime used to improve the solubility of dendritic moieties.

#### **2.3 Properties of soluble polyimides bearing long-chain alkyl groups**

From the continuous investigation in our laboratory, various precious data was obtained. The representative results are shown in this section.

## **2.3.1 Solubility**

8 Features of Liquid Crystal Display Materials and Processes

Fig. 5. Synthesis of aromatic diamines having multiple long-chain alkyl groups (dendritic

**2.3 Properties of soluble polyimides bearing long-chain alkyl groups** 

The representative results are shown in this section.

of soluble polyimides in our laboratory. BTDA, DSDA and 3,4'-ODPA, these are highly reactive and common aromatic tetracarboxylic dianhydrides were mainly used as a dianhydrides monomer, and DDE that is highly reactive and a common aromatic diamine was used as a diamine co-monomer. In the case of soluble polyimides, clear polyimide solutions were eventually obtained. In other cases, clear poly(amic acid) solutions were obtained, however, gelation or precipitation occurred in the course of imidization process. The polymerizations based on the dendritic diamine monomers, 12G1-AGterphenyldiamine and 12G2-AG-terphenyldiamine were firstly investigated using NMP as a solvent. Although viscous poly(amic acid)s solution were obtained, precipitation sometime occurred during the imidization process. It was speculated that the hydrocarbon and phenyl moiety of dendritic diamine monomers reduces the solubility of polyimides in NMP; therefore, a polar aromatic solvent, *m-*cresol or pyridine were sometime used to improve the

From the continuous investigation in our laboratory, various precious data was obtained.

terphenyl diamines)

solubility of dendritic moieties.

As far as the solublity of polyimides based on long-chain alkyl groups is concerned, the following interesting results have been obtained. Experimental results of homopolymerization and copolymerization based on BTDA/ADBP-12, AODB-12, DBAE-12, ADBA-12, DPABA-12/DDE are summarized in Table 1. Although all polyamic(acid)s were soluble in NMP which is a solvent used for polymerization, however, the solubility of homopolyimides and copolyimides depended on polymer structures. BTDA/ADBP-12 homopolyimides and BTDA/ADBP-12/DDE copolyimides containing 40 mol% of ADBP or more were soluble in NMP. Thus, the effect of long-chain alkyl group in ADBP for the enhancement of solubility was confirmed. BTDA/AODB-12 homopolyimides and BTDA/AODB-12/DDE copolyimides containing 25 mol% or more of AODB-12 units were also soluble in NMP. Judging from the results of copolymerization based on BTDA/ADBP-9~14/DDE and BTDA/AODB-10~14/DDE, it is recognized that AODB bearing alkyl groups *via* an ether linkage were more effective for the enhancement of solubility in comparison to ADBP.

On the other hand, all homopolyimides and copolyimide based on BTDA/DBAE-8~14/DDE were insoluble in NMP probably due to the rigid ester linkage groups. The experimental results of copolymerization based on BTDA/ADBA-12/DDE are quite unique. Although BTDA/ADBA-12 homopolyimide was insoluble, the copolymers, BTDA/ADBA-12/DDE (100/75/25) and BTDA/ADBA-12/DDE (100/50/50) were soluble in NMP. The solubility of these copolyimides may be improved by the randomizing effect based on copolymerization as well as the entropy effect of long chain linear alkyl groups. Based on the fact that all copolyimides BTDA/DBAE-8~14/DDE were insoluble in NMP, ADBA is more effective for the enhancement of solubility in comparison to DBAE. Fig. 6 summarizes the effect of functional diamines, AODB-X, ADBP-X, ADBA-X and DBAE-X bearing longchain alkyl groups for the enhancement of solubility investigated in our laboratory, and it is concluded that the effect of functional diamines are increased as AODB (ether linkage) > ADBP (benzoyl linkage) > ADBA (amide linkage) > DBAE (ester linkage) (Fig. 6). The polyimides and copolyimides based on BTDA, DPABA-6 or DPABA-12, and DDE containing 50 mol % or more DPABA were soluble, showing that the effect of DPABA for the enhancement of solubility was larger than ADBA. It is speculated that the three longchain alkyl groups in DPABA enhance the solubility of polyimides.

Furthermore, several important results concerning on the structure-solubility relationships of the polyimides bearing long-chain alkyl groups are obtained and concluded as follows: (1) ADBP with an even number of carbon atoms were effective in enhancing the solubility, while polymers based on ADBP with an odd number of carbon atoms remained insoluble. It can be assumed that the conformation around C-C bonds of the long-chain alkyl groups and alignment of benzene ring attached with these alkyl groups and carbonyl group affect this odd-even effect. (2) Copolymerization using the conventional aromatic diamine, DDE resulted in the improvement of both the molecular weight and the thermal stability. (3) The copolymerization study based on AODB-10~14 and DDE demonstrated that AODB-12 having 12 methylene units was the most effective in enhancing the solubility. (5) DBAE having branched alkyl chains such as nonan-5-yl 3,5-diaminobenzoate (DBAE-9-branch-A) and 2,6-dimethylheptane-4-yl 3,5-diaminobenzoate (DBAE-9-branch-B) were introduced in these polyimides, and the homopolyimides based on BTDA/ DBAE-9-branch-A and BTDA/ DBAE-9-branch-B, and copolyimides containing more than 50% of DBAE-9-branch-A or DBAE-9-branch-B were soluble in NMP. Thus, it was found that the introduction of branched alkyl chains enhances solubility.

Polyimides Bearing Long-Chain Alkyl Groups and

H2N NH2

O CXH2X+1

AODB-X

**High**

polymers.

be brittle.

**2.3.3 Spectral analysis** 

H2N NH2

O

was used for the ATR measurements of polyimide films.

ADBP-X

Their Application for Liquid Crystal Alignment Layer and Printed Electronics 11

ether linkage benzoyl linkage amide linkage ester linkage

CXH2X+1

Fig. 6. Effect of aromatic diamines bearing long-chain alkyl groups on polyimide solubility soluble polyimides in Table 1 are in the range of 0.16~0.65 dLg-1. The weight average molecular weights of the polyimides based on ADBA-12 and DPABA-12 determined by SEC measurements are in the range of 54200 to 119100. These values indicated that the molecular weights of these polyimides were considered to be medium or rather lower values for polyimides, however, all polyimides show good film formation ability. In almost all cases, the molecular weights increased with the percentage of DDE, i. e. highly reactive diamine. The representative SEC traces are shown in Fig. 7, indicating that copolyimides based on BTDA/ADBA-11/DDE have typical monomodal molecular weight distribution, and their polydispersity is in the range of 2.2-2.4, which are typical values for polycondensation

1H NMR spectra were measured on a JEOL JNM-AL400 FT NMR instrument in CDCl3 or dimethylsulfoxide-d6 with tetramethylsilane (TMS) as an internal standard. IR spectra were recorded on a JASCO FT/IR-470 plus spectrophotometer. ATR Pro 450-S attaching Ge prism

The polyimide film samples for the measurement of ATR and thermomechanical analysis (TMA) mentioned in the next section were prepared by the following casting method. About five wt % polyimide solution in appropriate solvents such as NMP, chloroform, *m*-cresol on aluminum cup or glass substrate and the solution were slowly evaporated by heating on a hotplate at appropriate temperature (*ca.* 50 °C for chloroform, *ca.* 150 °C for NMP and *m*cresol) until the films were dried, then the films were dried in a vacuum oven at 100 °C for 12 h. In case the molecular weights of polyimides were lower, the polyimide films tended to

In the case of soluble polyimides, NMR measurements are convenient because solution samples can be prepared, and provide more quantitative data. For example, Fig. 8 shows the 1H NMR spectrum of the copolyimide based on ADBA-12/DDE (50/50) that is soluble in DMSO-d6 and the peaks support this polymer structure. The intensity ratio of CH3 protons

H2N NH2

O N H

ADBA-X

CXH2X+1

DBAE-X

**Low**

H2N NH2

O O

CXH2X+1


aEquimolar amount of BTDA (3.3',4,4'-Benzophenonetetracarboxylic dianhydride) was used to the total molar amount of diamine. Reaction condition; r.t., 12 h poly(amic acid), Pyridine (5 molar) / Ac2O (4 molar), 120 oC. bMeasured at 0.5 g dL-1 in NMP at 30 oC. cMeasured by DSC at a heating rate of 20 oC/min in N2 on second heating. dMeasured by TGA at a heating rate of 10o C/min. eDetermined by SEC in NMP containning 10 mM LiBr using a series of polystyrenes standards having narrow polydispersities. f Softening temperature, measured by TMA at a heating rate of 10 oC/min

Table 1. Polyimides and copolyimides bearing long-chain alkyl groups

#### **2.3.2 Molecular weight**

As an index of molecular weight, the measurement of inherent viscosities (ηinh) and SEC measurement have been carried out in our laboratory. The inherent viscosities of all polymers were measured using Cannon Fenske viscometers at a concentration of 0.5 g/dL in NMP at 30 C. Size exclusion chromatography (SEC) measurements were performed in NMP containing 10mM LiBr at 40oC with a TOSOH HLC-8020 equipped with a TSK-GEL ALPHA-M. Number average molecular weight (*Mn*), weight average molecular weight (*Mw*) and polydispersity (*Mw/Mn*) were determined by TOSOH Multi Station GPC-8020 calibrated with a series of polystyrenes as a standard. For examples, ηinh values for the

Fig. 6. Effect of aromatic diamines bearing long-chain alkyl groups on polyimide solubility

soluble polyimides in Table 1 are in the range of 0.16~0.65 dLg-1. The weight average molecular weights of the polyimides based on ADBA-12 and DPABA-12 determined by SEC measurements are in the range of 54200 to 119100. These values indicated that the molecular weights of these polyimides were considered to be medium or rather lower values for polyimides, however, all polyimides show good film formation ability. In almost all cases, the molecular weights increased with the percentage of DDE, i. e. highly reactive diamine. The representative SEC traces are shown in Fig. 7, indicating that copolyimides based on BTDA/ADBA-11/DDE have typical monomodal molecular weight distribution, and their polydispersity is in the range of 2.2-2.4, which are typical values for polycondensation polymers.

## **2.3.3 Spectral analysis**

10 Features of Liquid Crystal Display Materials and Processes

<sup>b</sup> Tgc

50 50 0.66 soluble 0.57 247f 474 468 43700 97000 2.2 75 25 0.59 soluble 0.36 260f 452 435 27900 54200 1.9

50 50 0.83 soluble 0.65 253, 241f 453 446 45300 119100 2.6 75 25 0.60 soluble 0.39 325f 400 441 31500 77200 2.5 100 0 0.53 soluble 0.37 247f 352 429 25600 55300 2.2

aEquimolar amount of BTDA (3.3',4,4'-Benzophenonetetracarboxylic dianhydride) was used to the total molar amount of diamine. Reaction condition; r.t., 12 h poly(amic acid), Pyridine (5 molar) / Ac2O (4 molar), 120 oC. bMeasured at 0.5 g dL-1 in NMP at 30 oC. cMeasured by DSC at a heating rate of 20 oC/min in N2 on second heating. dMeasured by TGA at a heating rate of 10o C/min. eDetermined by SEC in NMP containning 10 mM LiBr using a series of polystyrenes standards having narrow

Softening temperature, measured by TMA at a heating rate of 10 oC/min

As an index of molecular weight, the measurement of inherent viscosities (ηinh) and SEC measurement have been carried out in our laboratory. The inherent viscosities of all polymers were measured using Cannon Fenske viscometers at a concentration of 0.5 g/dL in NMP at 30 C. Size exclusion chromatography (SEC) measurements were performed in NMP containing 10mM LiBr at 40oC with a TOSOH HLC-8020 equipped with a TSK-GEL ALPHA-M. Number average molecular weight (*Mn*), weight average molecular weight (*Mw*) and polydispersity (*Mw/Mn*) were determined by TOSOH Multi Station GPC-8020 calibrated with a series of polystyrenes as a standard. For examples, ηinh values for the

Table 1. Polyimides and copolyimides bearing long-chain alkyl groups

dLg-1 in NMP dLg-1 oC in Air in N2 *Mn Mw Mw/Mn* o

C <sup>o</sup>

10% Weight loss Polyimide

temperatured

C

Molecular Weighte

Poly(amic acid)

0 100 1.15 insoluble 25 75 0.44 insoluble

0 100 1.15 insoluble

0 100 1.15 insoluble 25 75 0.48 insoluble 50 50 0.45 insoluble 75 25 0.40 insoluble 100 0 0.31 insoluble

0 100 1.15 insoluble 25 75 0.95 insoluble

100 0 0.45 insoluble

0 100 1.15 insoluble 25 75 0.96 insoluble

<sup>b</sup> Solubility ηinh

50 50 0.49 soluble 0.37 264 467 500 75 25 0.49 soluble 0.46 261 469 481 100 0 0.34 soluble 0.37 254 468 464

25 75 0.39 soluble 0.29 262 460 456 50 50 0.21 soluble 0.23 264 456 457 75 25 0.14 soluble 0.19 284 447 452 100 0 0.14 soluble 0.16 277 436 441

Long-chain-DA DDE ηinh

mol%

Diaminea

ADBP-12

AODB-12

DBAE-12

ADBA-12

DPABA-12

polydispersities. f

**2.3.2 Molecular weight** 

1H NMR spectra were measured on a JEOL JNM-AL400 FT NMR instrument in CDCl3 or dimethylsulfoxide-d6 with tetramethylsilane (TMS) as an internal standard. IR spectra were recorded on a JASCO FT/IR-470 plus spectrophotometer. ATR Pro 450-S attaching Ge prism was used for the ATR measurements of polyimide films.

The polyimide film samples for the measurement of ATR and thermomechanical analysis (TMA) mentioned in the next section were prepared by the following casting method. About five wt % polyimide solution in appropriate solvents such as NMP, chloroform, *m*-cresol on aluminum cup or glass substrate and the solution were slowly evaporated by heating on a hotplate at appropriate temperature (*ca.* 50 °C for chloroform, *ca.* 150 °C for NMP and *m*cresol) until the films were dried, then the films were dried in a vacuum oven at 100 °C for 12 h. In case the molecular weights of polyimides were lower, the polyimide films tended to be brittle.

In the case of soluble polyimides, NMR measurements are convenient because solution samples can be prepared, and provide more quantitative data. For example, Fig. 8 shows the 1H NMR spectrum of the copolyimide based on ADBA-12/DDE (50/50) that is soluble in DMSO-d6 and the peaks support this polymer structure. The intensity ratio of CH3 protons

Polyimides Bearing Long-Chain Alkyl Groups and

O

50 mol% 50 mol%

O

C O N N

HA HB

O

O

NH

cooling from 250 oC.

Their Application for Liquid Crystal Alignment Layer and Printed Electronics 13

O

O

H2O NHCH2

Fig. 8. 1H NMR spectrum of a copolyimide based on BTDA/ADBA-12/DDE (100/50/50) 10 g load in the penetration mode using the film samples approximately 300 μm in thickness. Softening temperatures (Ts) were taken as the onset temperature of the probe displacement on the second TMA scan after cooling from 220 oC. Thermogravimetric analysis (TGA) was performed on a Shimadzu TGA-50 in air or under nitrogen (50 mL/min) at a heating rate of 10 °C/min using 5 mg of a dry powder sample, and 0 (onset), 5, 10% weight loss temperatures (Td0, Td5, Td10) were calculated from the second heating scan after

The Tg's of these polyimides sometimes were not recognized by DSC measurements, probably due to the rigid imide linkages. In these cases, TMA measurements were performed to determine the Tg. Many publications have described that the softening temperature (Ts) obtained from TMA measurements corresponds to the apparent Tg of polymers. As can be seen from Tables 1, the Tg values of these polyimides are in the range from 241-325 oC, showing similar values observed in soluble polyimides obtained from our laboratory (*ca.* around 250 oC) and are 100-150 oC lower than those of the conventional fully aromatic polyimides, however, are 100-150 oC higher than the commodity thermoplastics.

<sup>O</sup> <sup>N</sup> CH2CH2(CH2)9CH3

H

C O N N

O

HA HB

HA HB

(CH2)9

O

n n

DMSO

O

HB HA

HB HA

CH3

Fig. 7. Representative SEC traces of soluble polyimides based on aromatic diamines bearing long-chain alkyl groups. BTDA/ADBA-11/DDE (100/50/50): *Mn*, 49500; *Mw*, 118800; *Mw/Mn*, 2.4. BTDA/ADBA-11/DDE (100/75/25): *Mn*, 30700; *Mw*, 67900; *Mw/Mn*, 2.2

of long-chain alkyl groups and the aromatic proton HA or HB is approximately 3/4, meaning that copolymer composition corresponds to the monomers initial ratio. Imidization ratios of polyimides are generally determined by FT-IR measurements, comparing absorption intensities of amic acid carbonyl groups with those of imide carbonyl groups. However, FT-IR measurements give relatively less quantitative data in comparison with NMR measurements. In the case of these soluble polyimides, generally, a broad signal due to the NH protons of poly(amic acid) appears around 12 ppm in DMSO-d6, while this signal disappears in the corresponding polyimide. The imidization ratios of these polyimides can be calculated from the reduction in intensity ratio of the NH proton signals in poly(amic acid)s and these values for the polyimides prepared in our laboratory are sufficiently high, near to 100 %.

ATR measurement is the useful method to measure IR spectrum of polymer films. Representative ATR spectrum of dendronized polyimides based on 12G1-AG-Terphenyldiamine and 12G2-AG-Terphenyldiamine were shown in Fig. 9 and these spectrum show the strong absorptions based on C-H bonds of long-chain alky groups and the strong absorptions of C-O bonds of alkyloxy groups, and these absorption intensities become stronger with the increase of long-chain alkyl ether segments in the polyimides.

#### **2.3.4 Thermal properties**

Differential scanning calorimetery (DSC) traces were obtained on a Shimadzu DSC-60 under nitrogen (flow rate 30 mL/min) at a heating rate of 20o C/min and the glass transition temperatures (Tg) were read at the midpoint of the heat capacity jump from the second heating scan after cooling from 250 oC. Thermomechanical analysis (TMA) was performed on a Shimadzu TMA-50 under nitrogen (30 mL/min) at a heating rate of 10 oC/min with a

BTDA/ADBA-11/DDE (100/75/25)

BTDA/ADBA-11/DDE (100/50/50)

near to 100 %.

**2.3.4 Thermal properties** 

7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0

Fig. 7. Representative SEC traces of soluble polyimides based on aromatic diamines bearing long-chain alkyl groups. BTDA/ADBA-11/DDE (100/50/50): *Mn*, 49500; *Mw*, 118800; *Mw/Mn*, 2.4. BTDA/ADBA-11/DDE (100/75/25): *Mn*, 30700; *Mw*, 67900; *Mw/Mn*, 2.2

of long-chain alkyl groups and the aromatic proton HA or HB is approximately 3/4, meaning that copolymer composition corresponds to the monomers initial ratio. Imidization ratios of polyimides are generally determined by FT-IR measurements, comparing absorption intensities of amic acid carbonyl groups with those of imide carbonyl groups. However, FT-IR measurements give relatively less quantitative data in comparison with NMR measurements. In the case of these soluble polyimides, generally, a broad signal due to the NH protons of poly(amic acid) appears around 12 ppm in DMSO-d6, while this signal disappears in the corresponding polyimide. The imidization ratios of these polyimides can be calculated from the reduction in intensity ratio of the NH proton signals in poly(amic acid)s and these values for the polyimides prepared in our laboratory are sufficiently high,

ATR measurement is the useful method to measure IR spectrum of polymer films. Representative ATR spectrum of dendronized polyimides based on 12G1-AG-Terphenyldiamine and 12G2-AG-Terphenyldiamine were shown in Fig. 9 and these spectrum show the strong absorptions based on C-H bonds of long-chain alky groups and the strong absorptions of C-O bonds of alkyloxy groups, and these absorption intensities become stronger with the increase of long-chain alkyl ether segments in the polyimides.

Differential scanning calorimetery (DSC) traces were obtained on a Shimadzu DSC-60 under nitrogen (flow rate 30 mL/min) at a heating rate of 20o C/min and the glass transition temperatures (Tg) were read at the midpoint of the heat capacity jump from the second heating scan after cooling from 250 oC. Thermomechanical analysis (TMA) was performed on a Shimadzu TMA-50 under nitrogen (30 mL/min) at a heating rate of 10 oC/min with a

Log Mw

Fig. 8. 1H NMR spectrum of a copolyimide based on BTDA/ADBA-12/DDE (100/50/50)

10 g load in the penetration mode using the film samples approximately 300 μm in thickness. Softening temperatures (Ts) were taken as the onset temperature of the probe displacement on the second TMA scan after cooling from 220 oC. Thermogravimetric analysis (TGA) was performed on a Shimadzu TGA-50 in air or under nitrogen (50 mL/min) at a heating rate of 10 °C/min using 5 mg of a dry powder sample, and 0 (onset), 5, 10% weight loss temperatures (Td0, Td5, Td10) were calculated from the second heating scan after cooling from 250 oC.

The Tg's of these polyimides sometimes were not recognized by DSC measurements, probably due to the rigid imide linkages. In these cases, TMA measurements were performed to determine the Tg. Many publications have described that the softening temperature (Ts) obtained from TMA measurements corresponds to the apparent Tg of polymers. As can be seen from Tables 1, the Tg values of these polyimides are in the range from 241-325 oC, showing similar values observed in soluble polyimides obtained from our laboratory (*ca.* around 250 oC) and are 100-150 oC lower than those of the conventional fully aromatic polyimides, however, are 100-150 oC higher than the commodity thermoplastics.

Polyimides Bearing Long-Chain Alkyl Groups and

Their Application for Liquid Crystal Alignment Layer and Printed Electronics 15

Fig. 10. Representative TGA traces of dendronized polyimides based on 12G1-AG-Terphenyldiamine {(BTDA/12G1-AG-Terphenyldiamine/DDE (100/50/50)}

residual DCs were measured by C-V method using impedance analyzer.

follows: the polyimide solutions were spin-coated onto ITO glass substrates to a thickness of 0.1 μm, and cured at 210 °C for 10 minutes to produce liquid crystal alignment films. After the liquid crystal alignment films were subjected to a rubbing process, the alignment properties and the pretilt angles of the liquid crystal were measured. The surface of the alignment films were rubbed by means of a rubbing machine, two substrates were arranged anti-parallel to each other in such a manner that the rubbing direction of the each substrates were reverse, and the two substrates were sealed while maintaining cell gaps of 50 μm to fabricate liquid crystal cells. The liquid crystal cells were filled with the liquid crystalline compounds (Merk licristal). The alignment properties of the liquid crystal were observed under an orthogonally polarlized optical microscope. The pretilt angles of the liquid crystal were measured by a crystal rotation method. In order to examine the electrical properties, the test cells were prepared by the same manner as above except the cell gap, 5 μm. The voltage holding ratios were measured with VHRM 105 (Autronic Melchers). To evaluate the VHR, the applied frequency and voltage was 60 Hz, 1V with pulse of 64 μsec. The voltage versus transmittance and optical response properties, such like contrast ratio, response time, image sticking, etc., were measured using computer-controlled system in conjunction with an tungsten-halogen lamp, a function/arbitrary waveform generator, photomultiplier. The

The polyimide alignment layers containing 8 mol % of 12G1-AG-Terphenyldiamine were utilized for the vertical alignment mode (VA-mode). The synthesis of polyimide alignment layers containing 8 mol % of 12G1-AG-Terphenyldiamine was carried out in NMP as a solvent by conventional two step polymerization method regularly used for the synthesis of polyimide alignment layers for TN-LCDs , and 12G1-AG-Terphenyldiamine monomer was used as one of the diamine components. LCDs test cell properties are summarized in Table 2. PIA-DEN represents the test cell using the polyimide alighnment layers containing 8 mol % of 12G1-AG-Terphenyldiamine, and TN represents the test cell using the regular polyimide alignment layers. The pretilt angles of LC molecules were over 89° in PIA-DEN test cells, which are the suitable values for VAN-LCDs. It is speculated that an extremely

Fig. 9. Representative ATR spectrum of dendronized polyimides

Consequently, the physical heat resistance of these soluble polyimides bearing long-chain alkyl groups can be ranked as heat resistant polymers.

The Td10 values of these polyimides bearing long-chain alkyl groups in Table 1 are in the range 352~474 oC in air and 429~500 oC under nitrogen, showing similar values observed in soluble polyimides obtained from our laboratory (*ca.* 400~500 oC). In most cases, Td values in air were lower than Td values under nitrogen following the general fact that oxidative degradation proceed rapidly in air. As the incorporation of DDE resulted in a reduction of aliphatic components of the polyimides, the Td10 of these polyimides tends to increase with the increment of the DDE component (Table 1). These Td10 values of soluble polyimides obtained in our laboratory are 100~200 oC lower than those of wholly aromatic polyimides; however, the chemical heat resistance of these polyimides still can be ranked as heat resistant polymers. Fig. 10 shows the TGA traces of dendronized polyimides based on BTDA/12G1-AG-Terphenyldiamine (100/50/50). These TGA traces showed steep weight loss at the intial stage of degradation, and these weight loss percent almost correspond the calculated value of the weight percent of alkyl groups in polymer segments. Therefore, it is considered that the degradation of long-chain alkyl groups occurred at the initial stage of thermal degradation. Furthermore, these TGA traces also show the evidence that the longchain alkyl groups exist in the polyimides and the cleavage of alkyl groups did not occurred during the polymerization.

#### **2.4 Application for VAN-LCDs**

The alignment layer application for VAN-LCDs using polyimides having dendritic side chains was performed at Cheil Ind. Inc., Korea. LCDs test cell properties were measured as

Fig. 9. Representative ATR spectrum of dendronized polyimides

alkyl groups can be ranked as heat resistant polymers.

during the polymerization.

**2.4 Application for VAN-LCDs** 

Consequently, the physical heat resistance of these soluble polyimides bearing long-chain

The Td10 values of these polyimides bearing long-chain alkyl groups in Table 1 are in the range 352~474 oC in air and 429~500 oC under nitrogen, showing similar values observed in soluble polyimides obtained from our laboratory (*ca.* 400~500 oC). In most cases, Td values in air were lower than Td values under nitrogen following the general fact that oxidative degradation proceed rapidly in air. As the incorporation of DDE resulted in a reduction of aliphatic components of the polyimides, the Td10 of these polyimides tends to increase with the increment of the DDE component (Table 1). These Td10 values of soluble polyimides obtained in our laboratory are 100~200 oC lower than those of wholly aromatic polyimides; however, the chemical heat resistance of these polyimides still can be ranked as heat resistant polymers. Fig. 10 shows the TGA traces of dendronized polyimides based on BTDA/12G1-AG-Terphenyldiamine (100/50/50). These TGA traces showed steep weight loss at the intial stage of degradation, and these weight loss percent almost correspond the calculated value of the weight percent of alkyl groups in polymer segments. Therefore, it is considered that the degradation of long-chain alkyl groups occurred at the initial stage of thermal degradation. Furthermore, these TGA traces also show the evidence that the longchain alkyl groups exist in the polyimides and the cleavage of alkyl groups did not occurred

The alignment layer application for VAN-LCDs using polyimides having dendritic side chains was performed at Cheil Ind. Inc., Korea. LCDs test cell properties were measured as

Fig. 10. Representative TGA traces of dendronized polyimides based on 12G1-AG-Terphenyldiamine {(BTDA/12G1-AG-Terphenyldiamine/DDE (100/50/50)}

follows: the polyimide solutions were spin-coated onto ITO glass substrates to a thickness of 0.1 μm, and cured at 210 °C for 10 minutes to produce liquid crystal alignment films. After the liquid crystal alignment films were subjected to a rubbing process, the alignment properties and the pretilt angles of the liquid crystal were measured. The surface of the alignment films were rubbed by means of a rubbing machine, two substrates were arranged anti-parallel to each other in such a manner that the rubbing direction of the each substrates were reverse, and the two substrates were sealed while maintaining cell gaps of 50 μm to fabricate liquid crystal cells. The liquid crystal cells were filled with the liquid crystalline compounds (Merk licristal). The alignment properties of the liquid crystal were observed under an orthogonally polarlized optical microscope. The pretilt angles of the liquid crystal were measured by a crystal rotation method. In order to examine the electrical properties, the test cells were prepared by the same manner as above except the cell gap, 5 μm. The voltage holding ratios were measured with VHRM 105 (Autronic Melchers). To evaluate the VHR, the applied frequency and voltage was 60 Hz, 1V with pulse of 64 μsec. The voltage versus transmittance and optical response properties, such like contrast ratio, response time, image sticking, etc., were measured using computer-controlled system in conjunction with an tungsten-halogen lamp, a function/arbitrary waveform generator, photomultiplier. The residual DCs were measured by C-V method using impedance analyzer.

The polyimide alignment layers containing 8 mol % of 12G1-AG-Terphenyldiamine were utilized for the vertical alignment mode (VA-mode). The synthesis of polyimide alignment layers containing 8 mol % of 12G1-AG-Terphenyldiamine was carried out in NMP as a solvent by conventional two step polymerization method regularly used for the synthesis of polyimide alignment layers for TN-LCDs , and 12G1-AG-Terphenyldiamine monomer was used as one of the diamine components. LCDs test cell properties are summarized in Table 2. PIA-DEN represents the test cell using the polyimide alighnment layers containing 8 mol % of 12G1-AG-Terphenyldiamine, and TN represents the test cell using the regular polyimide alignment layers. The pretilt angles of LC molecules were over 89° in PIA-DEN test cells, which are the suitable values for VAN-LCDs. It is speculated that an extremely

Polyimides Bearing Long-Chain Alkyl Groups and

polyimides

**2.5 Application for printed electronics** 

Their Application for Liquid Crystal Alignment Layer and Printed Electronics 17

Fig. 12. Voltage-transmittance curves of LCD test cells using dendronized and conventional

Recently, various printing methods such as an ink-jet print method have been investigated for manufacturing polymeric thin-films, and the surface wettability and their control methods have become important. Thus, the author has investigated the surface wettability control of these polyimides by UV light irradiation that is a conventional method for microlithography (Fig. 13). The soluble polyimides bearing long-chain alkyl groups used for this study were synthesized from 12G1-AG-Terphenyldiamine, 3C10-PEPEDA, 3C10- PEPADA or 3C10-PAPADA that have three long-chain alkyl groups, aliphatic tetracarboxylic dianhydride; Cyclohexene-DA or aromatic tetracarboxylic dianhydride; DSDA or 3,4'- ODPA, and DDE as a diamine co-monomer. Polyimide thin-films were obtained as follows: 0.5-2.0 wt % polyimide solution in NMP were cast on glass substrates and the solution were slowly evaporated by heating at approximately 100-120 oC until the films were dried, then the films were dried in a vacuum oven at 100 oC for 12 h. Water contact angles were measured by SImage mini (Excimer. Inc., Japan) and UV light irradiation were performed using UV lamp unit E50-254-270U-1 (254 nm, 6.0 mW/cm2, Excimer. Inc., Japan) and a cool plate NCP-2215 (NISSIN Laboratory equipment, Japan) adjusted at 20oC that was used to neglect the effect of thermal degradation of polyimide films during UV irradiation process.


a Surface energy of polyimide alignment films measured by a contact angle metod

Table 2. LCDs test cell properties using the alignment films containing dendronized polyimides

bulky and hydrophobic dendritic moieties affects the generation of pretilt angles between the surface of polyimide and liquid crystalline molecules as illustrated in Fig. 11. The considerably lower surface energy value of the PIA-DEN alignment film in comparison with the one of TN mode also indicate that the surface of polyimides containing dendritic moieties is more hydrophobic.

The various important properties of PIA-DEN test cells such as voltage holding ratio (VHR), response time, contrast ratio, residual DC, and image sticking are equivalent or advantageous in comparison with those of regular TN test cell. Fig. 12 shows a V-T (voltagetransmittance) curve of these test cells, and shows a dramatic change of T. Consequently, it is convinced that the dendritic monomers, and dendritic polyimides developed by our research can be applied for the alignment films for VAN-LCDs.

PI alignment films having alkyl side chains for TN-LCDs

## Dendronized PI alignment films for VAN-LCDs

Fig. 11. Vertical alignment of LC molecules using dendronized polyimides as alignment layers

**ITEM PIA-DEN TN mode** 

Pretilt angle (°) >89 4~6 Surface energy (dyn/cm2)a 39 48 VHR (%) 25°C >99 >99 60°C >98 >95 Response time (ms) <25 <30 Contrast ratio 580 250 Residual DC (mv) <200 <200 Image sticking <1 <1

Table 2. LCDs test cell properties using the alignment films containing dendronized

bulky and hydrophobic dendritic moieties affects the generation of pretilt angles between the surface of polyimide and liquid crystalline molecules as illustrated in Fig. 11. The considerably lower surface energy value of the PIA-DEN alignment film in comparison with the one of TN mode also indicate that the surface of polyimides containing dendritic

The various important properties of PIA-DEN test cells such as voltage holding ratio (VHR), response time, contrast ratio, residual DC, and image sticking are equivalent or advantageous in comparison with those of regular TN test cell. Fig. 12 shows a V-T (voltagetransmittance) curve of these test cells, and shows a dramatic change of T. Consequently, it is convinced that the dendritic monomers, and dendritic polyimides developed by our

a Surface energy of polyimide alignment films measured by a contact angle metod

research can be applied for the alignment films for VAN-LCDs.

polyimides

moieties is more hydrophobic.

LC molecules

O O O NH <sup>O</sup> <sup>O</sup> <sup>O</sup>

layers

O O O NH <sup>O</sup> <sup>O</sup> <sup>O</sup>

O O O NH <sup>O</sup> <sup>O</sup> <sup>O</sup>

O O O NH <sup>O</sup> <sup>O</sup> <sup>O</sup>

Fig. 11. Vertical alignment of LC molecules using dendronized polyimides as alignment

PI alignment films having alkyl side chains for TN-LCDs

Dendronized PI alignment films for VAN-LCDs

O O O NH <sup>O</sup> <sup>O</sup> <sup>O</sup>

O O O NH <sup>O</sup> <sup>O</sup> <sup>O</sup>

O O O NH <sup>O</sup> <sup>O</sup> <sup>O</sup>

Alkyl side chains

Fig. 12. Voltage-transmittance curves of LCD test cells using dendronized and conventional polyimides

#### **2.5 Application for printed electronics**

Recently, various printing methods such as an ink-jet print method have been investigated for manufacturing polymeric thin-films, and the surface wettability and their control methods have become important. Thus, the author has investigated the surface wettability control of these polyimides by UV light irradiation that is a conventional method for microlithography (Fig. 13). The soluble polyimides bearing long-chain alkyl groups used for this study were synthesized from 12G1-AG-Terphenyldiamine, 3C10-PEPEDA, 3C10- PEPADA or 3C10-PAPADA that have three long-chain alkyl groups, aliphatic tetracarboxylic dianhydride; Cyclohexene-DA or aromatic tetracarboxylic dianhydride; DSDA or 3,4'- ODPA, and DDE as a diamine co-monomer. Polyimide thin-films were obtained as follows: 0.5-2.0 wt % polyimide solution in NMP were cast on glass substrates and the solution were slowly evaporated by heating at approximately 100-120 oC until the films were dried, then the films were dried in a vacuum oven at 100 oC for 12 h. Water contact angles were measured by SImage mini (Excimer. Inc., Japan) and UV light irradiation were performed using UV lamp unit E50-254-270U-1 (254 nm, 6.0 mW/cm2, Excimer. Inc., Japan) and a cool plate NCP-2215 (NISSIN Laboratory equipment, Japan) adjusted at 20oC that was used to neglect the effect of thermal degradation of polyimide films during UV irradiation process.

Polyimides Bearing Long-Chain Alkyl Groups and

Monomer

Tetracarboxylic dianhydridea

Cyclohexene-DA

3,4'-ODPA

(deg) after rinsing by isopropyl alcohol.

0

20

40

60

Water contact angle [°]

80

100

DSDA

Their Application for Liquid Crystal Alignment Layer and Printed Electronics 19

0J 2J 4J 6J 8J

a Equimolar amount of tetracarboxylic dianhydride was used to the total amount of diamines. b Water contact angles (deg) using contact angle meter (Excimer inc.,SImage mini)at 25℃. c Water contact angles

3,4'-ODPA / 3C10-PEPADA/DDE

02468

UV irradiation energy [J]

Table 3. Water contact angles of the polyimide surface after irradiation of UV light

100/100/0

100/50/50

100/0/100

Fig. 14. UV irradiation energy dependence of water contact angles of polyimide films

100 0 104 (101) 96 (92) 95 (83) 86 (67) 81 (50) 50 50 97 (96) 95 (81) 87 (64) 68 (59) 57 (38) 0 100 80 (80) 73 (75) 67 (60) 58 (50) 38 (24)

Polyimide Water contact angle after UV irradiation <sup>b</sup>

, ( ) <sup>c</sup>

100 0 104 (104) 88 (79) 76 (64) 60 (45) 44 (33) 50 50 99 (95) 87 (76) 81 (72) 62 (60) 45 (54)

100 0 100 (99) 80 (75) 57 (57) 36 (30) 24 (23) 50 50 96 (94) 80 (73) 52 (57) 31 (32) 31 (30) 0 100 78 (78) 77 (75) 44 (70) 42 (63) 36 (52)

3C10-PEPADA DDE

Diamine mol%

3C10-PEPADA DDE

0 100 3C10-PEPADA DDE

Fig. 13. Conceptual scheme of wettability control of the polyimide surface by UV irradiation

Thus, the polyimide thin films were irradiated by UV light, and the contact angles for the water decreased from near 100° (hydrophobicity) to the minimum value, 20° (hydrophilicity) in proportion to irradiated UV light energy. The thin film specimens after UV light irradiation were rinsed by isopropyl alcohol. The representative results using the polyimides based on 3C10-PEPADA are summarized in Table 3 and Fig. 14.

Although the water contact angles decreased after UV light irradiation, the degrees of changes depended on the polyimide structures. For examples, the contact angles of the polymides based on 3,4'-ODPA or DSDA/ 3C10-PEPADA /DDE remarkably decreased from around 100o to around 20-30o after UV light irradiation (254nm, 2-8J). These changes were less in the case of the polyimides based on Cyclohexene-DA/3C10-PEPADA /DDE, and the changes were much less in the case of the polyimides based on Cyclohexene-DA/ DDE without long-chain alkyl groups.

It is considered that these changes of wettability of polyimides are mainly based on the photo-degradation or scission of long-chain alkyl groups, and that the generation of the hydrophilic functional groups such as COOH and OH groups occurred. ATR measurements

Fig. 13. Conceptual scheme of wettability control of the polyimide surface by UV irradiation Thus, the polyimide thin films were irradiated by UV light, and the contact angles for the water decreased from near 100° (hydrophobicity) to the minimum value, 20° (hydrophilicity) in proportion to irradiated UV light energy. The thin film specimens after UV light irradiation were rinsed by isopropyl alcohol. The representative results using the

Although the water contact angles decreased after UV light irradiation, the degrees of changes depended on the polyimide structures. For examples, the contact angles of the polymides based on 3,4'-ODPA or DSDA/ 3C10-PEPADA /DDE remarkably decreased from around 100o to around 20-30o after UV light irradiation (254nm, 2-8J). These changes were less in the case of the polyimides based on Cyclohexene-DA/3C10-PEPADA /DDE, and the changes were much less in the case of the polyimides based on Cyclohexene-DA/

It is considered that these changes of wettability of polyimides are mainly based on the photo-degradation or scission of long-chain alkyl groups, and that the generation of the hydrophilic functional groups such as COOH and OH groups occurred. ATR measurements

polyimides based on 3C10-PEPADA are summarized in Table 3 and Fig. 14.

DDE without long-chain alkyl groups.


a Equimolar amount of tetracarboxylic dianhydride was used to the total amount of diamines. b Water contact angles (deg) using contact angle meter (Excimer inc.,SImage mini)at 25℃. c Water contact angles (deg) after rinsing by isopropyl alcohol.

Table 3. Water contact angles of the polyimide surface after irradiation of UV light

## 3,4'-ODPA / 3C10-PEPADA/DDE

Fig. 14. UV irradiation energy dependence of water contact angles of polyimide films

Polyimides Bearing Long-Chain Alkyl Groups and

Fig. 16. XPS narrow scan of 3,4'-ODPA / 3C10-PEPADA

Their Application for Liquid Crystal Alignment Layer and Printed Electronics 21

3,4'-ODPA/3C10-PEPADA (0 J)

3,4'-ODPA/3C10-PEPADA (6 J)

Fig. 17. SFM images of 3,4'-ODPA /DDE and 3,4'-ODPA /3C10-PAPADA

UV (254 nm)

of the polyimide surfaces after UV light irradiation support this assumption, and the absorption of OH groups around 3300 cm-1 increase, the absorption of alkyl groups around 2900 cm-1 decrease, and the absorption of ether groups around 1200 cm-1 decrease with the increase in the photo-irradiation energy (Fig. 15). The intensive surface analysys was examined using XPS and SFM. XPS measurements were carried out on an XPS -APEX (Physical Electronics Co. Ltd.) with an Al Kα X-ray source (150 W). Chamber pressure; 10-9 - 10-10 Pa; take off angles; 45o and SFM (SII Nanotechnology Inc., SPA 400) was operated in a dynamic force microscopic (DFM) mode. The generation of hydrophilic moieties was analyzed in detail by XPS narrow scan, and chemical shifts due to C-O and C=O bonds clearly increase after UV light irradiation (Fig. 16). The surface nm size roughness probably based on long-chain alky groups was observed by SFM analysis (Fig. 17), however, these micro roughness seemed not to change after UV light irradiation. Thus, the change of surface wettability of polyimides is occurred mainly by the changes of chemical structures of polyimide surface. It is speculated that the complicated photo-induced reactions such as auto-oxidation, cleavage of ester groups, Fries rearrangement, etc. occur on the surface of polyimides on the course of UV light irradiation (Fig. 18).

In conclusion, the surface wettability of polyimides bearing long-chain alkyl groups can be controlled by UV light irradiation, and these methods are expected to be applied in the field of printed electronics.

Fig. 15. Representative ATR spectrum of polyimides bearing long-chain alkyl groups before and after UV irradiation

of the polyimide surfaces after UV light irradiation support this assumption, and the absorption of OH groups around 3300 cm-1 increase, the absorption of alkyl groups around 2900 cm-1 decrease, and the absorption of ether groups around 1200 cm-1 decrease with the increase in the photo-irradiation energy (Fig. 15). The intensive surface analysys was examined using XPS and SFM. XPS measurements were carried out on an XPS -APEX (Physical Electronics Co. Ltd.) with an Al Kα X-ray source (150 W). Chamber pressure; 10-9 - 10-10 Pa; take off angles; 45o and SFM (SII Nanotechnology Inc., SPA 400) was operated in a dynamic force microscopic (DFM) mode. The generation of hydrophilic moieties was analyzed in detail by XPS narrow scan, and chemical shifts due to C-O and C=O bonds clearly increase after UV light irradiation (Fig. 16). The surface nm size roughness probably based on long-chain alky groups was observed by SFM analysis (Fig. 17), however, these micro roughness seemed not to change after UV light irradiation. Thus, the change of surface wettability of polyimides is occurred mainly by the changes of chemical structures of polyimide surface. It is speculated that the complicated photo-induced reactions such as auto-oxidation, cleavage of ester groups, Fries rearrangement, etc. occur on the surface of

In conclusion, the surface wettability of polyimides bearing long-chain alkyl groups can be controlled by UV light irradiation, and these methods are expected to be applied in the field

Fig. 15. Representative ATR spectrum of polyimides bearing long-chain alkyl groups before

polyimides on the course of UV light irradiation (Fig. 18).

of printed electronics.

and after UV irradiation

Fig. 16. XPS narrow scan of 3,4'-ODPA / 3C10-PEPADA

Fig. 17. SFM images of 3,4'-ODPA /DDE and 3,4'-ODPA /3C10-PAPADA

Polyimides Bearing Long-Chain Alkyl Groups and

the field of printed electronics.

**4. Acknowledgment** 

gratefully acknowledged.

0032-3896

April 2010

601, ISSN 0032-3896

941-947, ISSN 0032-3896

2008), pp. 354-366, ISSN 0032-3896

5031-5053, ISSN 1422-0067

**5. References** 

Their Application for Liquid Crystal Alignment Layer and Printed Electronics 23

near 20° (hydrophilicity) in proportion to irradiated UV light energy. From the result of surface analyses, it is recognized that the hydrophobic long-chain alkyl groups on the polyimide surface decrease and the hydrophilic groups such as a hydroxyl group generate on their surface. Thus, the surface wettability of polyimides bearing long-chain alkyl groups can be controlled by UV light irradiation, and these methods are expected to be applied in

The author thanks Dr. Atsushi Takahara of Kyushu University, Drs. Takaaki Matsuda and Tsutomu Ishi-I of Kurume National College of Technology for various advices. The author also thanks many students of Kurume National College of Technology for their help with the experiments. Financial supports from Cheil Industries Inc., Kyushu Industrial Technology Center, DYDEN Corporation, and Toyohashi University of Technology are

Tsuda, Y., Kawauchi, T., Hiyoshi, N. & Mataka, S. (2000a). Soluble Polyimides Based on

Tsuda, Y., Kanegae, K. & Yasukouchi, S. (2000b). Soluble Polyimides Based on

Tsuda, Y., Kojima, M. & OH, J.-M. (2006). Soluble Polyimides Based on Diaminobenzoic Acid

Tsuda, Y., Kojima, M., Matsuda, T. & OH, J.-M. (2008). Soluble Polyimides Based on Long-

Tsuda, Y. (2009). Soluble Polyimides Based on Aromatic Diamines Bearing Long-chain Alkyl

Tsuda, Y., OH, J.-M. & Kuwahara, R. (2009). Dendronized Polyimides Bearing Long-chain

Tsuda, Y., Nakamura, R., Osajima, S. & Matsuda, T. (2010). Surface Wettability Controllable

Tsuda, Y., Hashimoto & Matsuda, T. (2011a). Surface Wettability Controllable Polyimides

(Ed.), pp. 17-42,VSP/Brill, ISBN 978-90-04-17080-3, Leiden

*(Japanese),* Vol. 68 (January 2011), pp. 24-32, ISSN 0386-2186

Alkyldiaminobenzophenone. *Polymer Journal.* Vol. 32, No. 7, (June 2000), pp. 594-

Alkyloxydiaminobenzene. *Polymer Journal.* Vol. 32, No. 11, (November 2000), pp.

Alkylester. *Polymer Journal.* Vol. 38, No. 10, (October 2000), pp. 1043-1054, ISSN

chain Alkyl Groups *via* Amide Linkages. *Polymer Journal.* Vol. 40, No. 4 (April

Groups, In: *Polyimides and Other High Temperature Polymers. Vol. 5,* Mittal, K. L.

Alkyl Groups and Their Application for Vertically Aligned Nematic Liquid Crystal Displays. *International Journal of Molecular Sciences.* Vol. 10 (November 2009), pp.

Polyimides Bearing Long-chain Alkyl Groups by UV Light Irradiation. *PMSE Preprints (ACS Division Proceeding Online)*, Vol. 239, ISSN 1550-6703, San Francisco,

Bearing Long-chain Alkyl Groups by UV Light Irradiation. *Kobunshi Ronbunshu* 

Fig. 18. Anticipated photochemical reactions on the surface of polyimides

## **3. Conclusion**

The synthesis, characterizations, basic properties and applications of soluble polyimide bearing long-chain alkyl groups are reviewed in this chapter. These polyimides are successfully obtained based on the novel aromatic diamine monomers having long-chain alkyl groups. As these polyimides are soluble in various organic solvents, the spectral analyses such as NMR are possible, and the polymer structures are well characterized. The basic properties of these polyimides such as the solubility and the thermal stability are investigated in detail and the structure-properties relationships are well considered. Thus, it is concluded that these polyimides bearing long-chain alkyl groups are suitable polymeric materials for microelectronics applications.

The application as alignment layers for LCDs was investigated, and it was found that these polyimides having dendritic side chains were applicable for the vertically aligned nematic liquid crystal displays (VAN-LCDs). It is speculated that an extremely bulky and hydrophobic dendron moiety affects the generation of vertical alignment.

The thin films of polyimides bearing three long-chain alkyl groups were irradiated by UV light , and the contact angles for the water decreased from near 100° (hydrophobicity) to near 20° (hydrophilicity) in proportion to irradiated UV light energy. From the result of surface analyses, it is recognized that the hydrophobic long-chain alkyl groups on the polyimide surface decrease and the hydrophilic groups such as a hydroxyl group generate on their surface. Thus, the surface wettability of polyimides bearing long-chain alkyl groups can be controlled by UV light irradiation, and these methods are expected to be applied in the field of printed electronics.

## **4. Acknowledgment**

22 Features of Liquid Crystal Display Materials and Processes

Fig. 18. Anticipated photochemical reactions on the surface of polyimides

hydrophobic dendron moiety affects the generation of vertical alignment.

The synthesis, characterizations, basic properties and applications of soluble polyimide bearing long-chain alkyl groups are reviewed in this chapter. These polyimides are successfully obtained based on the novel aromatic diamine monomers having long-chain alkyl groups. As these polyimides are soluble in various organic solvents, the spectral analyses such as NMR are possible, and the polymer structures are well characterized. The basic properties of these polyimides such as the solubility and the thermal stability are investigated in detail and the structure-properties relationships are well considered. Thus, it is concluded that these polyimides bearing long-chain alkyl groups are suitable polymeric

The application as alignment layers for LCDs was investigated, and it was found that these polyimides having dendritic side chains were applicable for the vertically aligned nematic liquid crystal displays (VAN-LCDs). It is speculated that an extremely bulky and

The thin films of polyimides bearing three long-chain alkyl groups were irradiated by UV light , and the contact angles for the water decreased from near 100° (hydrophobicity) to

**3. Conclusion** 

materials for microelectronics applications.

The author thanks Dr. Atsushi Takahara of Kyushu University, Drs. Takaaki Matsuda and Tsutomu Ishi-I of Kurume National College of Technology for various advices. The author also thanks many students of Kurume National College of Technology for their help with the experiments. Financial supports from Cheil Industries Inc., Kyushu Industrial Technology Center, DYDEN Corporation, and Toyohashi University of Technology are gratefully acknowledged.

## **5. References**


**2** 

*Japan* 

**Transparent ZnO Electrode** 

**for Liquid Crystal Displays** 

*Research Institute, Kochi University of Technology* 

Naoki Yamamoto, Hisao Makino and Tetsuya Yamamoto

Recently, the scarcity and toxicity of indium, a major constituent element of ITO, has become a concern. Indium is a rare element that ranks 61st in abundance in the Earth's crust (Kempthorne & Myers 2007). In addition, the major amounts of indium consumed by the industries produceing the electronic devices such as liquid crystal displays (LCDs), touchscreens and solar cell systems are supplied by only a few countries. Furthermore, indium has also been suspected to induce lung disease, and particularly indium-related pulmonary

Transparent conductive oxides have become the focus of attention as a substitute material for ITO currently used for optically transparent electrodes in electronic devices. In particular, transparent conductive ZnO films are expected to be suitable materials to achieve such purposes because, in contrast with indium as a major constituent element of ITO, Zn is an element that the human body requires and is a component of some marketed beverages, in addition to having being used for years in cosmetics and as a vulcanization accelerator for rubber products such as tires. Furthermore, conductive and transparent ZnO films have low electrical resistance and high optical transmittance comparable with those of ITO films reported by some authors (Wakeham et al., 2009; Shin et al., 1999). We have developed the technology to form transparent conductive ZnO films with low resistance (2.4 m for a 100 nm thick film (Yamada, et al., 2007)), optical transmittance exceeding 95% (film-only transmittance without that of the glass substrate) and high heat-resistance (thermally stable until 300-450 °C (Yamamoto, N. et al., 2010)). The technology of transparent conductive ZnO films applied as alternatives to ITO electrodes for LCD panels is described in this chapter.

Ga-doped ZnO (GZO) and Al-doped (AZO) films have been widely studied as the most promising transparent conductive films as alternatives to ITO films used in electronics

Conventional magnetron sputtering systems, planar- and cylindrical-types (Carousel-type), were used to form transparent ZnO thin films. A schematic diagram of the cylindrical-type magnetron sputtering system is shown in Fig. 1 (a). In the cylindrical-type magnetron

**1. Introduction** 

fibrosis should be paid attention (Homma et al., 2005).

**2. Preparation of transparent and conductive ZnO film** 

devices such as LCDs, LEDs and solar cells.

**2.1 Magnetron sputtering system** 

Tsuda, Y. (2011b). Surface Wettability Controllable Polyimides Bearing Long-chain Alkyl Groups by UV Light Irradiation. Proceedings of International Conference on Materials for Advanced Technologies, ISBN 978-981-08-8878-7, SUNTEC Singapore, June 2011.
