**2.1 The setup of electrosynthesis**

To take advantage of electrosynthesis, many efforts are needed to design the electrolytic apparatus. The paper6 briefly introduces the setup of electropolymerization. Here we present the details of the apparatus.

The setup consists of four parts (Scheme1). The DC power can operate under two modes: the constant current mode and the constant voltage mode. We usually choose the constant current mode. The commutator can change the polarity of the electrodes in the range of 5 ~ 60 seconds. The supplied electricity is counted by a coulometer. When a predetermined electric volume is reached, it will cut off the electric supply to the electrolytic cell. A detailed description of the cell is plotted in Scheme 2.

Electropolymerization of Polysilanes with Functional Groups 3

The MeSiCl3 and allyl chloride were put in a compartment cell equipped with Mg cathodes, mechanic stirrer and thermograph. Then THF and LiClO4 (0.05M) were added. All reactions were carried out under dry nitrogen atmosphere in order to eliminate the oxygen. Constant current electrolysis was applied at room temperature. During the electroreduction the electrolysis cell was sonicated and the polarity of electrodes was periodically alternated. The supplied amount of electricity was counted by a coulometer. Electrolysis was terminated at the desired amount of electricity. Then a quantity of toluene was poured in the cell and adequate gaseous ammonia was introduced to react with the residual Si-Cl. The solution was filtrated to remove MgCl2 precipitate, and then was vacuum distilled to remove THF in the solvent. Subsequently, the residue was filtrated again to remove insoluble material. Finally, toluene was evaporated at reduced pressure, in each case to yield the light yellow

> ))), r.t. Mg electrode

Polysilane without double bonds (EPS2) was synthesized in the same way using only

The products were identified using GPC (Agilent1100 American) with THF as solvent, 1H NMR (AV-500), XRD (D/Max-rc Japan) and FTIR (Thermo Nicolet-AVRTAR370FT-IR).

Half an hour later after the monomers are plunged into the reaction bottle, the electrodes are charged. A small amount of sample is drawn out at intervals. It is hydrolyzed, and then titrated with sodium hydroxide solution. Therefore, the content of Si-Cl bonds in the bottle is determined. By following the variation of the Si-Cl bonds, we can analyze the reaction rate

In the following episodes, the various factors influencing the reaction will be discussed in

The influence of the MeSiCl3/allyl chloride ratio on the yield, remaining double bonds, and

The optimum molar ratio of MeSiCl3/H2C=CHCH2Cl was 3/1 where the highest yield, double bonds concentration and molecular weight were reached. The relatively low yield and molecular weight at ratio of 10/1 and 5/1, where allyl chloride was deficient, might be due to the intramolecular reaction of MeSiCl3. This reaction led to highly cross-linked structure, which was insoluble in solvent. Only the low molecular weight fraction was

n/2

Si CH3

Si CH3

CH2 CHCH2

**2.2.1 Electropolymerization and isolation** 

liquid, polysilane with double bonds (EPS1). The reaction scheme is shown as follows:

Cl <sup>+</sup> <sup>n</sup> CH2 <sup>m</sup> CHCH2Cl

FTIR spectra were measured using KBr method.

**2.2.2 Influential factors of electrosynthesis** 

**2.2.2.1 Effect of molar ratios of monomers** 

Mw of polysilanes is shown in Table 1.

Scheme 3. Electrosynthesis of polysilane with double bonds

The measurement of monomer reaction rate is as follows:

The double bond content was determined by bromine addition method11.

Si CH3

of the electropolymerization.

detail.

MeSiCl3 as monomer for comparison.

Cl

Cl

Scheme 1. The structure of the setup

Scheme 2. The scheme of the electrolytic cell 1. N2 bottle (99.99%) 2.drying tower (molecular sieve) 3.drying tower (CaCl2) 4.ultrasonic 5.electrode 6. rubber plug 7. N2 inlet 8.stirrer 9.motor 10.feeding hole 11.thermometer

The rectangle electrodes are 40mm long, 30mm wide and 10mm thick. It is rubbed with emery cloth before use. The space between the two poles is fixed by inserting two hollow polyethylene tubes (Φ4mm), and the electrodes and the tubes are binded together with nylon wire. The power of the ultrasonic (20 kHz) is 100W.

#### **2.2 Electropolymerization of polysilanes with double bonds**

The introduction of double bonds will increase the ceramic yield, shorten the production period of the C/C-SiC composites, and diminish the mechanical damage to the composites. We will discuss in detail the influential factors in the reaction and characterize the reaction product.

#### **2.2.1 Electropolymerization and isolation**

2 Electropolymerization

Scheme 2. The scheme of the electrolytic cell 1. N2 bottle (99.99%) 2.drying tower (molecular sieve) 3.drying tower (CaCl2) 4.ultrasonic 5.electrode 6. rubber plug 7. N2 inlet 8.stirrer

The rectangle electrodes are 40mm long, 30mm wide and 10mm thick. It is rubbed with emery cloth before use. The space between the two poles is fixed by inserting two hollow polyethylene tubes (Φ4mm), and the electrodes and the tubes are binded together with

The introduction of double bonds will increase the ceramic yield, shorten the production period of the C/C-SiC composites, and diminish the mechanical damage to the composites. We will discuss in detail the influential factors in the reaction and characterize the reaction

Scheme 1. The structure of the setup

9.motor 10.feeding hole 11.thermometer

product.

nylon wire. The power of the ultrasonic (20 kHz) is 100W.

**2.2 Electropolymerization of polysilanes with double bonds** 

The MeSiCl3 and allyl chloride were put in a compartment cell equipped with Mg cathodes, mechanic stirrer and thermograph. Then THF and LiClO4 (0.05M) were added. All reactions were carried out under dry nitrogen atmosphere in order to eliminate the oxygen. Constant current electrolysis was applied at room temperature. During the electroreduction the electrolysis cell was sonicated and the polarity of electrodes was periodically alternated. The supplied amount of electricity was counted by a coulometer. Electrolysis was terminated at the desired amount of electricity. Then a quantity of toluene was poured in the cell and adequate gaseous ammonia was introduced to react with the residual Si-Cl. The solution was filtrated to remove MgCl2 precipitate, and then was vacuum distilled to remove THF in the solvent. Subsequently, the residue was filtrated again to remove insoluble material. Finally, toluene was evaporated at reduced pressure, in each case to yield the light yellow liquid, polysilane with double bonds (EPS1).

The reaction scheme is shown as follows:

$$\begin{array}{ccccc} \text{Cl} & & & \text{CH}\_{2} \overset{=\text{CHCH}\_{2}}{\longrightarrow} & \text{Cl}\_{2} \overset{=\text{CHCH}\_{2}}{\longrightarrow} & & \\ \text{In Cl} & \text{Si} & \text{CH}\_{2} \overset{=\text{CHCH}\_{2}\text{Cl}}{\longrightarrow} & \text{Cl} & \text{Si} & \text{Si} \\ \text{Cl} & & & & \\ \end{array}$$

Scheme 3. Electrosynthesis of polysilane with double bonds

Polysilane without double bonds (EPS2) was synthesized in the same way using only MeSiCl3 as monomer for comparison.

The products were identified using GPC (Agilent1100 American) with THF as solvent, 1H NMR (AV-500), XRD (D/Max-rc Japan) and FTIR (Thermo Nicolet-AVRTAR370FT-IR). FTIR spectra were measured using KBr method.

The double bond content was determined by bromine addition method11.

The measurement of monomer reaction rate is as follows:

Half an hour later after the monomers are plunged into the reaction bottle, the electrodes are charged. A small amount of sample is drawn out at intervals. It is hydrolyzed, and then titrated with sodium hydroxide solution. Therefore, the content of Si-Cl bonds in the bottle is determined. By following the variation of the Si-Cl bonds, we can analyze the reaction rate of the electropolymerization.

#### **2.2.2 Influential factors of electrosynthesis**

In the following episodes, the various factors influencing the reaction will be discussed in detail.

#### **2.2.2.1 Effect of molar ratios of monomers**

The influence of the MeSiCl3/allyl chloride ratio on the yield, remaining double bonds, and Mw of polysilanes is shown in Table 1.

The optimum molar ratio of MeSiCl3/H2C=CHCH2Cl was 3/1 where the highest yield, double bonds concentration and molecular weight were reached. The relatively low yield and molecular weight at ratio of 10/1 and 5/1, where allyl chloride was deficient, might be due to the intramolecular reaction of MeSiCl3. This reaction led to highly cross-linked structure, which was insoluble in solvent. Only the low molecular weight fraction was

Electropolymerization of Polysilanes with Functional Groups 5

1. EPS1:polysilane with double bonds synthesized with the MeSiCl3/H2C=CHCH2Cl ratio

1H NMR spectrum of polysilane with double bonds (Fig.2) has four major peaks near δ 0.09, 0.25, 0.55 and 0.85 ppm, these are chemical shifts of Si-CH3. The broad and complication of these peaks are due to the complex structures around the Si-CH3 groups. The observed peaks near δ 5.8, 5.1-5.2, and 3.8-3.9 are the characteristic chemical shifts for Si-allyl moiety13.

2. EPS2:polysilane without double bonds synthesized with the MeSiCl3

This proves the presence of double bonds in polysilane.

Fig. 2. 1H NMR spectrum of polysilane with double bonds

**2.2.2.2 Effect of monomer concentration** 

Table 2. Effect of monomer concentration

**2.2.2.3 Effect of electrode materials** 

Monomer

networks, which would precipitate from solution.

The following experiments were performed on MeSiCl3/Allyl Chloride ratio of 3:1.

Under different monomer concentrations, the polysilanes were synthesized with 5% theoretical electricity. As shown in Table 2, the yield and molecular weight of the polysilanes became lower with increase of concentration. When the concentration was higher, MeSiCl3 was apt to polymerize with itself, forming giant three dimensional

concentration 1M 2M 3M Yield, % 93 72 49 Mw, Dalton 1723 861 474 Mw /Mn 4.89 2.29 1.33

The electrode materials have a profound influence on the formation of polysilanes. As Table 3 shows, the entry using Mg anode and cathode gave the highest molecular weight and

The following experiments were performed at 1M monomer concentration.

of 3:1


soluble and obtainable as product. As the molar ratio surpassed 3/1, the excessive allyl chloride, acting as end capping agent, blocked the propagation of polysilane chains, resulting in lower molecular weight.

a MeSiCl3 monomer concentration was 1M , 10% theoretical charge was applied, and cathodes were Mg ingots.

Table 1. Effect of molar ratios of monomersa

The IR spectra of polysilanes are showed in Fig.1. The polysilane with and without double bonds both have C-H stretching (2960 and 2920cm-1) groups, C-H bending (1450 and 1410cm-1) groups, Si-CH3 (1260 and 790cm-1), Si-Si (460cm-1). These absorptions imply the presence of Si-Si and Si-CH3 bonds in both polysilanes. The presence of Si-O-Si (1080cm-1) linkages was the consequence of the polymers' reactivity toward oxygen during work-up. The absorptions at 1640cm-1 of C=C stretching groups in the curve (1) indicate the presence of double bonds12.

Fig. 1. FT-IR spectra of polysilanes with and without double bonds

soluble and obtainable as product. As the molar ratio surpassed 3/1, the excessive allyl chloride, acting as end capping agent, blocked the propagation of polysilane chains,

(MeSiCl3/H2C=CHCH2Cl) 10/1 5/1 3/1 2/1 3/2

Yield, % 49 51 84 71 79

bonds, % 7.4 9.1 12.6 11.3 8.2 Mw, Dalton 1625 1974 3749 2293 834 Mw /Mn 3.19 3.84 8.26 4.52 1.64 a MeSiCl3 monomer concentration was 1M , 10% theoretical charge was applied, and cathodes were Mg

The IR spectra of polysilanes are showed in Fig.1. The polysilane with and without double bonds both have C-H stretching (2960 and 2920cm-1) groups, C-H bending (1450 and 1410cm-1) groups, Si-CH3 (1260 and 790cm-1), Si-Si (460cm-1). These absorptions imply the presence of Si-Si and Si-CH3 bonds in both polysilanes. The presence of Si-O-Si (1080cm-1) linkages was the consequence of the polymers' reactivity toward oxygen during work-up. The absorptions at 1640cm-1 of C=C stretching groups in the curve (1) indicate the presence

3000 2500 2000 1500 1000 500

C=C

)

Wavenumbers(cm-1

Si-Si

Si-Si

resulting in lower molecular weight.

Table 1. Effect of molar ratios of monomersa

(2)

Fig. 1. FT-IR spectra of polysilanes with and without double bonds

(1)

Ratio of

Retaining ratio of double

ingots.

of double bonds12.


1H NMR spectrum of polysilane with double bonds (Fig.2) has four major peaks near δ 0.09, 0.25, 0.55 and 0.85 ppm, these are chemical shifts of Si-CH3. The broad and complication of these peaks are due to the complex structures around the Si-CH3 groups. The observed peaks near δ 5.8, 5.1-5.2, and 3.8-3.9 are the characteristic chemical shifts for Si-allyl moiety13. This proves the presence of double bonds in polysilane.

Fig. 2. 1H NMR spectrum of polysilane with double bonds

The following experiments were performed on MeSiCl3/Allyl Chloride ratio of 3:1.

#### **2.2.2.2 Effect of monomer concentration**

Under different monomer concentrations, the polysilanes were synthesized with 5% theoretical electricity. As shown in Table 2, the yield and molecular weight of the polysilanes became lower with increase of concentration. When the concentration was higher, MeSiCl3 was apt to polymerize with itself, forming giant three dimensional networks, which would precipitate from solution.


Table 2. Effect of monomer concentration

The following experiments were performed at 1M monomer concentration.

#### **2.2.2.3 Effect of electrode materials**

The electrode materials have a profound influence on the formation of polysilanes. As Table 3 shows, the entry using Mg anode and cathode gave the highest molecular weight and

Electropolymerization of Polysilanes with Functional Groups 7

listed in Table 4. With increase of the amount of electricity, the molecular weight rose stepwise and the molecular weight distributions became broader. The broader Mw /Mn might be due to the heterogeneous reaction condition and multiple reaction paths14. The results indicate that the polysilanes with different molecular weight can be obtained by

Yield, % 87 92 85 Mw, Dalton 1723 2687 3952 Mw /Mn 4.89 6.58 8.67

The electroreduction was carried out under ultrasound with different interval times of 8s, 17s and 26s, respectively. As shown in Fig. 4, the molecular weights of the products became higher with decreasing of the interval time. It could be explained that the alternation of anode and cathode might overcome the difficulty of keeping the electric current at a suitable level due to the increase of the voltage between anode and cathode with progress of the reaction6. The maximum voltage was relatively lower at shorter interval time. The lower voltage reduced the possibility of side reactions, thus benefiting the propagation of Si-Si

100 1000 10000

(1)

(2)

(3)

Molar mass(Dalton)

Fig. 4. Effect of interval time on the products' GPC spectra (1) *Mw* =2432, interval time 26s;

(2) *Mw* =3031, interval time 17s; (3) *Mw* =6980, interval time 8s;

electricity

10% theoretic electricity

controlling the amount of electricity.

Table 4. Effect of the amount of electricity

**2.2.2.5 Effect of interval time** 

of electricity 5% theoretic electricity 7.5% theoretic

The amount

bonds.

yield. Aluminum was less effective than Mg, and Cu the worst. It was said that Mg played some important roles in the formation of the Si-Si bond6. Although details of the role of Mg in the mechanism of formation of the Si-Si bond are not clear now, the unique reactivity of Mg electrode is undoubtedly shown in this reaction.


a The polysilane were synthesized with 10% theoretic electric charge and interval time 17s.

Table 3. Effect of electrode materials a

The following experiments were performed with Mg electrodes.

#### **2.2.2.4 Effect of the amount of electricity**

The molecular weight was monitored at the different amount of electricity during the reaction process (Fig. 3). The molecular weight went up rapidly before 3% theoretical electricity (1440C\*mol-1) and entered a linear increasing period afterwards. This suggests that electrochemical synthesis of polysilane is a step-growth polymerization.

#### Fig. 3. The change of molecular weight of polysilane with the amount of electricity increasing

The amount of electricity is one of the most important factors to control the formation of Si-Si bond. The polymers, synthesized with different proportion of theoretical electricity, are listed in Table 4. With increase of the amount of electricity, the molecular weight rose stepwise and the molecular weight distributions became broader. The broader Mw /Mn might be due to the heterogeneous reaction condition and multiple reaction paths14. The results indicate that the polysilanes with different molecular weight can be obtained by controlling the amount of electricity.


Table 4. Effect of the amount of electricity

#### **2.2.2.5 Effect of interval time**

6 Electropolymerization

yield. Aluminum was less effective than Mg, and Cu the worst. It was said that Mg played some important roles in the formation of the Si-Si bond6. Although details of the role of Mg in the mechanism of formation of the Si-Si bond are not clear now, the unique reactivity of

materials Mg-Mg Mg-Al Al-Al Mg-Cu Yield, % 85 78 34 18 Mw, Dalton 3952 1099 898 512 Mw /Mn 8.67 3.36 2.12 1.63

The molecular weight was monitored at the different amount of electricity during the reaction process (Fig. 3). The molecular weight went up rapidly before 3% theoretical electricity (1440C\*mol-1) and entered a linear increasing period afterwards. This suggests

0 1000 2000 3000 4000 5000

the amount of reactive electricity(C\*mol-1)

Fig. 3. The change of molecular weight of polysilane with the amount of electricity

The amount of electricity is one of the most important factors to control the formation of Si-Si bond. The polymers, synthesized with different proportion of theoretical electricity, are

a The polysilane were synthesized with 10% theoretic electric charge and interval time 17s.

that electrochemical synthesis of polysilane is a step-growth polymerization.

The following experiments were performed with Mg electrodes.

Mg electrode is undoubtedly shown in this reaction.

Table 3. Effect of electrode materials a

150

increasing

200

250

300

Mw

350

400

450

**2.2.2.4 Effect of the amount of electricity** 

Electrode

The electroreduction was carried out under ultrasound with different interval times of 8s, 17s and 26s, respectively. As shown in Fig. 4, the molecular weights of the products became higher with decreasing of the interval time. It could be explained that the alternation of anode and cathode might overcome the difficulty of keeping the electric current at a suitable level due to the increase of the voltage between anode and cathode with progress of the reaction6. The maximum voltage was relatively lower at shorter interval time. The lower voltage reduced the possibility of side reactions, thus benefiting the propagation of Si-Si bonds.

Fig. 4. Effect of interval time on the products' GPC spectra (1) *Mw* =2432, interval time 26s; (2) *Mw* =3031, interval time 17s; (3) *Mw* =6980, interval time 8s;

Electropolymerization of Polysilanes with Functional Groups 9

The result above indicates polymerization can happen without electricity. To evaluate the role of electricity in the synthesis, the synthetic reactions of EPS1 and EPS2 with and without electricity were pursued (Fig. 6). The Si-Cl content in the case of electricity (curve b and d) is 5% ~ 13% less than that without electricity (curve a and c). In the whole electrosynthesis, the Grignard reaction between monomers and Mg ingot is in the majority, its ratio being as high as 80% ~ 90%. This result implies that the amount of charge passed could be much lower

0 100 200 300

(a)EPS2 without electricity (b)EPS2 with electricity (c)EPS1 without electricity (d)EPS1 with electricity

Reaction time (min)

The reaction mechanism for synthesis of polysilane through Wurtz route has been studied in the past few decade15. However, the mechanism by electrochemical route is scarcely reported16. According to above-mentioned, we speculate the mechanism might be divided into two parts. The first part is the Grignard reaction mechanism (Scheme 4). The monomers can react with Mg to form Grignard reagent, which again react with CH3SiCl3 to produce a

Another part is the electropolymerization mechanism (Scheme 5). The reactions include the electrode reaction and thermal reaction. First, the monomer gains an electron, being reduced to anion. The anion changes to silicon radical by eliminating chlorine anion, which can react

**2.2.2.8 Comparison of the rates of electrosynthesis with and without electricity** 

(a)

(d)

Fig. 6. Reaction rate of EPS1 and EPS2 with and without electricity

large molecule. The process repeats to form polysilane.

(b)

(c)

than that of the theoretical one to fulfill the electrosynthesis.

**2.2.3 On the reaction mechanism** 

Per Cent of Si-Cl bonds remaining(%)

#### **2.2.2.6 Effect of the concentration of supporting electrolyte**

The increase in the concentration of supporting electrolyte resulted in the growth of molecular weight and yield (Table 5). Higher concentration of supporting electrolyte brought on lower electrode voltage to maintain constant current, thus reducing side reaction. The 0.05M concentration seemed reasonable because the acquired molecular weight and yield were satisfying, and even higher concentration leads to higher cost as the recovery of costly LiClO4 is difficult.


Table 5. Effect of concentration of supporting electrolyte

#### **2.2.2.7 The rate of electrosynthesis of polysilane**

As shown in Fig.5, the EPS1 with double bonds has similar reaction tendency as the EPS2 without double bonds. About 30% ~ 40% Si-Cl had consumed at 0 mA\*h of electricity because of the Grignard reaction between monomers and Mg in THF. The rate of electrosynthesis was relatively quicker in 0~100 mA\*h range. The reaction finished as the amount of electricity reached 400 mA\*h (30% of the theoretical amount of electricity). The EPS1 with double bonds reacted faster than the EPS2 without double bonds. At the same electricity volume, the Si-Cl content of EPS1 was 10% ~ 15% less than that of EPS2. The reason for this is that the allyl chloride might change into allyl anion by gaining electrons, then the obtained allyl anion initiates the anion polymerization of polysilane, thus increasing the reaction rate.

Fig. 5. Reaction Rate of EPS1 and EPS2 by Electroreduction

The increase in the concentration of supporting electrolyte resulted in the growth of molecular weight and yield (Table 5). Higher concentration of supporting electrolyte brought on lower electrode voltage to maintain constant current, thus reducing side reaction. The 0.05M concentration seemed reasonable because the acquired molecular weight and yield were satisfying, and even higher concentration leads to higher cost as the

electrolyte (LiClO4) 0.05M 0.03M 0.005M Yield, % 91 81 72 Mw, Dalton 3031 1309 665 Mw /Mn 7.89 2.56 1.42

As shown in Fig.5, the EPS1 with double bonds has similar reaction tendency as the EPS2 without double bonds. About 30% ~ 40% Si-Cl had consumed at 0 mA\*h of electricity because of the Grignard reaction between monomers and Mg in THF. The rate of electrosynthesis was relatively quicker in 0~100 mA\*h range. The reaction finished as the amount of electricity reached 400 mA\*h (30% of the theoretical amount of electricity). The EPS1 with double bonds reacted faster than the EPS2 without double bonds. At the same electricity volume, the Si-Cl content of EPS1 was 10% ~ 15% less than that of EPS2. The reason for this is that the allyl chloride might change into allyl anion by gaining electrons, then the obtained allyl anion initiates the anion polymerization of polysilane, thus

0 100 200 300 400

Amount of charge passed(mA\*h)

 EPS1 EPS2

**2.2.2.6 Effect of the concentration of supporting electrolyte** 

Table 5. Effect of concentration of supporting electrolyte

**2.2.2.7 The rate of electrosynthesis of polysilane** 

recovery of costly LiClO4 is difficult.

Concentration of supporting

increasing the reaction rate.

0

Fig. 5. Reaction Rate of EPS1 and EPS2 by Electroreduction

10

20

30

40

Per Cent of Si-Cl bonds remaining(%)

50

60

70

80

#### **2.2.2.8 Comparison of the rates of electrosynthesis with and without electricity**

The result above indicates polymerization can happen without electricity. To evaluate the role of electricity in the synthesis, the synthetic reactions of EPS1 and EPS2 with and without electricity were pursued (Fig. 6). The Si-Cl content in the case of electricity (curve b and d) is 5% ~ 13% less than that without electricity (curve a and c). In the whole electrosynthesis, the Grignard reaction between monomers and Mg ingot is in the majority, its ratio being as high as 80% ~ 90%. This result implies that the amount of charge passed could be much lower than that of the theoretical one to fulfill the electrosynthesis.

Fig. 6. Reaction rate of EPS1 and EPS2 with and without electricity

#### **2.2.3 On the reaction mechanism**

The reaction mechanism for synthesis of polysilane through Wurtz route has been studied in the past few decade15. However, the mechanism by electrochemical route is scarcely reported16. According to above-mentioned, we speculate the mechanism might be divided into two parts. The first part is the Grignard reaction mechanism (Scheme 4). The monomers can react with Mg to form Grignard reagent, which again react with CH3SiCl3 to produce a large molecule. The process repeats to form polysilane.

Another part is the electropolymerization mechanism (Scheme 5). The reactions include the electrode reaction and thermal reaction. First, the monomer gains an electron, being reduced to anion. The anion changes to silicon radical by eliminating chlorine anion, which can react

Electropolymerization of Polysilanes with Functional Groups 11

\_ Cl-

. . . .

]

Si Cl

Cl

Si Cl

Cl

CH3

Cl

<sup>n</sup> . <sup>+</sup> 1e. Si (

n Cl **chain growth**

Cl

Cl

CH3

) Si Cl

CH3 <sup>n</sup> . . \_

CH3 Cl Si

CH3 Cl Si

CH3

CH3 Si Cl [Cl Cl

> Si Cl

**Thermal Processes 1:Nucleophilic Substitution**

CH3\_ Cl ..

**Electrode Processes 1:Monomer Reactions**

CH3 Si Cl Cl Cl

> Si Cl

. Cl

CH3 Si Cl

> Si Cl

Si Cl

> Si Cl

> > Si ( Cl

Si ( Cl

CH3 Si

Si ( Cl

CH3 Cl Si

Cl

**Intermolecular**

Cl

CH3

) Si Cl

CH3 <sup>n</sup> . .

CH3 Cl Si

Cl

**Thermal Processes 2 Intramolecular**

CH3

) Si Cl

Cl

CH3 <sup>n</sup> . . \_

CH3

) Si Cl

CH3

<sup>n</sup> Cl <sup>+</sup> 1e. Si (

\_ Si (

Cl

Scheme 5. Proposed reaction mechanism for electropolymerization of CH3SiCl3

Cl

CH3

) Si Cl

CH3

CH3 Cl Si

**Electrode Processes 2:Oligomer Reactions**

Cl

Cl

CH3

) Si Cl

CH3

**cross-linking**

CH3 Cl Si

CH3 Cl Si

CH3

Cl . CH3

CH3 . Cl .

\_

CH3 Cl <sup>+</sup> 1e

Cl Cl <sup>+</sup> 1e

. .

with magnesium ion from sacrificing anode. The formed silicon radical might gain another electron to change into silicon anion intermediate. This intermediate reacts with other monomers by nucleophilic substitution to form oligomers, which can also be reduced to silicon anions. In the process of chain elongation, the delocalization of the electron along the chain makes it easier for the reduction of the oligomer. The thermal process includes the nucleophilic substitution of silicon anion with monomer or oligomer, and the coupling reaction between radicals. The nucleophilic substitution may happen intramolecularly or intermolecularly. The intramolecular one leads to cross-linking, while the intermolucular makes the chain to grow.

Scheme 4. The proposed reaction mechanism for Grignard reaction of CH3SiCl3

with magnesium ion from sacrificing anode. The formed silicon radical might gain another electron to change into silicon anion intermediate. This intermediate reacts with other monomers by nucleophilic substitution to form oligomers, which can also be reduced to silicon anions. In the process of chain elongation, the delocalization of the electron along the chain makes it easier for the reduction of the oligomer. The thermal process includes the nucleophilic substitution of silicon anion with monomer or oligomer, and the coupling reaction between radicals. The nucleophilic substitution may happen intramolecularly or intermolecularly. The intramolecular one leads to cross-linking, while the intermolucular

AllylMgCl

Cl

AllylMgCl+CH3SiCl3 +MgCl2

+CH3SiCl3 Cl Si Si

CH3

Si Cl

Allyl

Cl

CH3 CH3

Cl

Cl +MgCl2

Cl

Cl

makes the chain to grow.

EPS1: AllylCl+Mg THF

CH3SiMgCl

Cl

Cl

EPS2: CH3SiCl3+Mg THF CH3SiMgCl

Scheme 4. The proposed reaction mechanism for Grignard reaction of CH3SiCl3

#### **Electrode Processes 1:Monomer Reactions**

#### **Thermal Processes 1:Nucleophilic Substitution**

#### **Electrode Processes 2:Oligomer Reactions**

#### **Thermal Processes 2**

**Intramolecular**

Scheme 5. Proposed reaction mechanism for electropolymerization of CH3SiCl3

Electropolymerization of Polysilanes with Functional Groups 13

The EPS3, being synthesized with the monomers of MeSiCl3, allyl chloride, cyclopentadiene and ZrCl4 in the ratio of 1:1/3:1/5:1/5, had the element contents (Wt%): 48.8%Si, 42.6%C, 4.1%Zr and a little oxygen. The retaining ratio of double bonds was 10.8% and the product

The GPC analysis result and viscosity of EPS2 and EPS3 is listed in Table 6. As a result of the introduction of Zr increased the size of the polysilane. Both the EPS2 and EPS3 can dissolve

Sample *Mw* /(Dalton) *Mw* / *Mn* Viscosity/(mPa.s/25℃)

EPS2 1723 1.89 75

EPS3 3749 3.24 125

The IR absorption of EPS3 at 1405cm-1 corresponds to Si-Cp23 and the 1640cm-1 peak

The UV maximum absorptions of EPS3 and EPS4 shift to red, being broadening and higher, compared with EPS2 (Fig.8). The first reason for this phenomenon is the delocalization of the double bonds of the allyl groups, which increases the σ-π conjugation between the backbone and the side groups. Next the Cp group can conjugate with the main chain, making it bigger the whole conjugation system of the molecule. Thus the electron-transfer energy is lowered, causing significant spectral red shifts into the accessible UV region. Furthermore, the big π bond formed between Zr and Cp makes the conjugation system even

y

Si Si Si

EPS3

CH3

CHCH2 CH2

y

CH3

M

CH3

Si Si Si

CH3

CH2 CHCH2

+ m Si Si Si

y

MClx

Scheme 6. Electrosynthesis of polysilane containing refractory metals

**2.3.2 Characterization of the Zr-containing polysilane** 

Table 6. Molecular weight and Shear viscosity of EPS2 and EPS3

CH3

CH3

CH2 CHCH2

yield was 71.2%.

in toluene, THF and chloroform.

corresponds to the C=C stretching(Fig.7).

wider, leading to still broader adsorption peak.
