Methylstyrene Polymerization and Characterization

The key requirements for using Si-Cl functional initiators to produce polymers carrying Si Cl termini by carbenium ion polymerization are i) Si-Cl should be inert toward aUcylaluminum coinitiators, ii) Si-Cl should not react with propagating carbenium ions, in) chain transfer to monomer should be negligible so as to end up with one Si-Cl head-group per polymer chain. 

A series of orienting experiments have been carried out to find suitable conditions for the synthesis of CISi-PaMeSt with desired molecular weight and terminal functionality. Conditions and results are shown in Table 3. 

Results of these orienting experiments compiled in Table 3 in regard to the effect of temperature, medium polarity, initiator concentration, monomer concentration, and coinitiator concentration are similar to those reported by others36 39 for cationic polymerization of a-methylstyrene. For example, decreasing temperature, the molecular weight increases and increasing medium polarity, the yield increases. 

Head-group functionality of CISi-PaMeSt prepared by this Si-Cl containing functional initiator 1 in conjunction with Et2AlCl was investigated. The amount of Si-Cl head-group was determined by conductometry of the HC1 generated by hydrolysis of CISi-PaMeSt, and the theoretical amount of Si-Cl was calculated from the sample weight and Mn of CISi-PaMeSt. The results are shown in Table 4, where the Effective Functionality E. F. is2 

According to these results the yields and E. F. decrease with the increasing number of Si-Cl bonds in the functional initiators. It is possible that Si-Cl bonds may slowly react with the diethylaluminum chloride coinitiator and thus reduce the expected E.F. as follows40  

---