**2.1. Materials**

Vanillin and 4, 4'-methylene diphenyl diisocyanate (MDI) were purchased from Aldrich Co. (United States). Rubeanic Acid (dithiooxiamide) and 4-hydroxybenzaldehyde were obtained from MERCK Co. (Germany). Polyethylene glycol with molecular weight of 3000, 2000 and 1000 (PEG: Mn= 3000, 2000 and 1000) were purchased from Fluka Chemica (Switzerland). All the chemicals were utilized as received without any further purification. N,N-Dimethylformamide purchased from Aldrich (United States) was distilled over Calcium Hydride (CaH2) through vacuum distillation before being used.

#### **2.2. Synthesis of monomers and polymers**

#### *2.2.1. Synthesis of 2,5-bis(4-hydroxyphenyl)thiazolo-[5,4d] thiazole (I)*

Briefly, 3 g (25 mmol) of dithiooxamide (Rubeanic acid) and 15 g (123 mmol) of 4 hydroxybenzaldehyde with the presence of 9 g (97 mmol) of phenol were charged all at once in a 500 ml round bottom flask fitted with condenser and left to be refluxed for 2h. Precipitates were obtained by pouring the hot mixtures to the cold water. Subsequently, the yield was filtered off and washed with ethanol followed by ether. The product obtained was dried at 70oC in a vacuum oven for 24 hours. Recrystallization from cyclohexanone was performed giving an orange-yellowish powder. Yield: 35% with melting point 364oC. Fourier transform infrared (FTIR; KBr, cm-1): 3492 (-OH), 1606 (C=N), 1596 (C=C), 855 (*p*-substituted benzene). 1H-NMR (400 MHz, DMSO-d*6* ppm): δH 7.12 (m, aromatic protons), 9.8 (s, -OH). Elemental analysis: Found: C, 59.16; H, 3.28; N, 8.84, C16H10N2O2S2 Calc.: C, 58.89; H, 3.09, N, 8.59.

#### *2.2.2. Synthesis of 2,5-bis(4-hydroxy-3-methoxyphenyl) thiazolo [5,4d] thiazole (II)*

The same procedure was applied to the synthesis of 2,5-bis(4-hydroxy-3-methoxyphenyl) thiazolo [5,4d] thiazole except that 4-hydroxybenzaldehyde was substituted with vanillin. Orange-yellowish powder was obtained as the end product. Yield: 26% with the melting point of 259oC. Fourier transform infrared (FT-IR; KBr disc): 3534 cm-1 (OH), 1608 cm-1(C=N), 1510 cm-1 (C=C), 842 cm-1 (-CH out of plane). 1H-NMR (400 MHz, DMSO-d*6* ppm): δH 7.09 (m, aromatic protons), 9.5 (s, -OH) and 3.87 (s, OCH3). Elemental analysis: Found: C, 55.60; H, 4.03; N, 6.89, C18H14N2O4S2 Calc.: C, 55.95; H, 3.62, N, 7.25.

#### *2.2.3. Synthesis of liquid crystalline polyurethane elastomers (LCPUE)*

Preparation of LCPUE was achieved by two steps solution polymerization reaction, where isocyanate terminated pre-polymer was synthesized initially in the first stage. To produce pre-polymer, 0.01 mol of PEG (Mw = 1000, 2000, and 3000) and 0.02 mol of MDI were mixed in 500ml of reactor flask equipped with condenser, thermometer, nitrogen inlet and mechanical stirrer. The mixture was allowed to be stirred and heated for 4h at 70oC in the presence of 15 ml of DMF as solvent and nitrogen gas was kept flowing to provide inert atmosphere. The reaction was followed by chain extension process, using either compound (I) or (II), where the chain extender was added dropwise within 1h to complete the formation of LCPUE. Subsequently, the temperature was increased to 100oC and the reaction continued for another 9 hr. The hot viscous solution was then poured into 200ml of cold water for precipitation, before subjected to filtration. Later, the filtered product was washed with ethanol several times and finally with ether, before being dried overnight in a vacuum oven at 60o C.

#### **2.4. Measurements**

20 Polyurethane

**2. Experimental** 

**2.1. Materials** 

characteristics for biomedical applications (Barikani et.al., 2009). Despite all the great aforementioned properties, modifications and improvements are done to conventional PUE

Diisocyanates, polyol and low molecular weight diamine or diol (chain extender) are the basic building blocks of conventional PUE (Yeganeh & Mehdizadeh, 2009). In order to synthesize liquid crystal polyurethane elastomers (LCPUE), the low molecular weight diamine or diol used in conventional PUE was substituted with the mesogenic unit. Incorporation of geometrically anisotropic moieties (mesogenic unit) within polymer architecture can drive the formation of liquid crystalline phase from strictly steric repulsion considerations (Abe & Ballauf, 1991; Rowan & Mather, 2007). Furthermore, the insertion of mesogenic unit in the backbone of PUE will impart unique physical properties to the polymer and also improve its

Various mesomorphic behaviors are exhibited with different types of mesogenic units in preparation of LCPUE. In this research work, mesogens consumed were thiazolo [5.4d] thiazoles based and it is known as an important class of biycyclic aromatic molecule comprising two fused thiazole rings (Knighton et.al., 2010). Thiazolothiazole rigid fused ring can enhance the rigidity of the polymer and the conjugation (Osaka et.al, 2007) which makes it a best candidate to be part of the hard segment in the LCPUE network. The hard segments consisted of either 2,5-bis(4-hydroxyphenyl) thiazolo-[5,4d] thiazole or 2,5-bis(4-hydroxy-3 methoxyphenyl) thiazolo [5,4d] thiazole and 4,4'- methylene diphenyl diisocyanate (MDI). As for the soft segments, polyethylene glycol (PEG) 1000, 2000 and 3000 were involved.

The ultimate aim of this work is to synthesize new LCPUE with the presence of thiazolo- [5,4d] thiazole as a chain extender. Study and analysis were carried out to determine the effects and consequences of the introduction of thiazolo-[5,4d] thiazole moiety and the

Vanillin and 4, 4'-methylene diphenyl diisocyanate (MDI) were purchased from Aldrich Co. (United States). Rubeanic Acid (dithiooxiamide) and 4-hydroxybenzaldehyde were obtained from MERCK Co. (Germany). Polyethylene glycol with molecular weight of 3000, 2000 and 1000 (PEG: Mn= 3000, 2000 and 1000) were purchased from Fluka Chemica (Switzerland). All the chemicals were utilized as received without any further purification. N,N-Dimethylformamide purchased from Aldrich (United States) was distilled over Calcium

Briefly, 3 g (25 mmol) of dithiooxamide (Rubeanic acid) and 15 g (123 mmol) of 4 hydroxybenzaldehyde with the presence of 9 g (97 mmol) of phenol were charged all at once

in order to meet the qualities in more advanced applications.

mechanical, optical and electrical characteristics (Jia et.al., 1996).

influence of various lengths of polyols on the properties of LCPUE.

Hydride (CaH2) through vacuum distillation before being used.

*2.2.1. Synthesis of 2,5-bis(4-hydroxyphenyl)thiazolo-[5,4d] thiazole (I)* 

**2.2. Synthesis of monomers and polymers** 

100mg mixture of samples and KBr (grounded) were pressed into translucent disc before being subjected to Nicolar Avatar Model 360 Fourier Transform infrared spectrometer devices to obtain FT-IR spectra. Data was collected in the range of 4000-400cm-1. 1H-NMR and 13C-NMR spectra were obtained using Bruker 400 MHz NMR spectrometer consuming DMSO-d*6* as solvent and TMS as internal standard. Thermal stability of LCPUE was determined by thermogravimetric analyzer (Perkin Elmer Pyris series 6) under nitrogen purge and with 10oC/min of heating rate and the heating was done up to 800oC. Liquid crystalline behavior was verified by means of differential scanning calorimetry (DSC) to

observe the behavior of polymers such as glass transition point (Tg), melting point (Tm) and isotropic temperature (Ti). It was conducted utilizing Perkin Elmer Pyris Series 7 thermal analyzer under Nitrogen flux at 100C/min rate of heating. Textures of mesomorphic phases were displayed by Nikon Eclipse E600 polarized microscope equipped with MS600 Linkam Hot stage and SONY CCD-IRIS Color Video Camera. The heating rate was 5oC/min and 10oC/min for the cooling rate. Sample was placed between two thin round glasses and it was then transferred onto microscope fitted with the hot stage to be analyzed. Siemens X-ray Diffractometer model D5000 equipped with a CuKα target at 40KV and 40mA was used in obtaining X-ray scattering curve. Tensile strain properties of LCPUE films were measured by Instron Testing instrument at a constant speed of 500mm/min (speed) where the measurements were performed at room temperature. Brookfield viscometer was used to measure the fluid viscosity where suitable spindle and speed were chosen and it was also performed at room temperature.

New Liquid Crystalline Polyurethane Elastomers

Containing Thiazolo [5,4d] Thiazole Moiety: Synthesis and Properties 23

LCPUE based on thiazolo [5,4d] thiazoles moiety were synthesized from long chain of diol (PEG 3000, 2000 and 1000) with an excess of diisocyanate (MDI) via addition reaction to give the terminal reactive group which results in the formation of 'extended diisocyanate' or isocyanate pre-polymer. Then, 2,5-bis(4-hydroxyphenyl) thiazolo-[5,4d] thiazole [I] and 2,5 bis(4-hydroxy-3- methoxyphenyl) thiazolo [5,4d] thiazole [II] were added acting as a chain extender in order to convert the pre-polymer into long chain LCPUE. The general route for the preparation of LCPUE was outlined in Scheme 2, yield and viscosity of LCPUE were listed in Table 1 and the data showed that the range of the viscosities and yields obtained were 10,744 to 40 692 cP and 76-87 %, respectively. Range of the viscosities obtained also provides the information of the molecular weight of each polymer synthesized where high value of viscosity indicates high molecular weight of the polymer produced and vice versa (Bagheri & Pourmoazzen, 2008). In this case, all LCPUE samples displayed fairly high

molecular weight in accordance with the results demonstrated.

**Scheme 2.** General route for the preparation of LCPUE VI (a-c) and VII (a-c)

FT-IR was employed to verify functional groups of the pre-polymer, compound I and II, and LCPUE. Prior to the formation of LCPUE which is referring to the pre-polymer state, in the region of 2270 cm-1 a peak was observed which was assigned to –N=C=O-

**3.3. Structural elucidation** 

**3.2. Polymer synthesis** 
