Synthesis and Characterization of Carboxyl Terminated Polydimethylsiloxanes

A series of hydrogen terminated polydimethylsiloxanes (PDMS-H) had been controlled synthesized via ring-opening polymerization. Then, methylmethacrylate (MMA) and tert-butyl methacrylate (tBMA) were grafted to PDMS-H via hydrosilylation reactions in the presence of Speier's catalyst, the hydrosilylation addition patterns of MMA and tBMA showed a strong preference toward -1,2 addition, no -1,2 addition product or 1,4-addition product was observed. Carboxyl terminated polydimethylsiloxanes were prepared by subsequent hydrolysis reaction in an aqueous NaOH/ethanol solution and under acid condition, respectively. Both methods could obtain carboxyl terminated polydimethylsiloxanes successfully. However, a significant decrease of the molecular weight of products was observed in the alkaline hydrolysis process, while the acid hydrolysis of tertiary butyl ester group terminated polydimethylsiloxanes could be conducted in a highly controlled manner. Besides, the synthesis of carboxyl terminated polydimethylsiloxanes via acid hydrolysis reaction can be conducted well only when the terminal group of polydimethylsiloxanes is tertiary butyl, this can be explained by the specificity of tertiary butyl.