Interfacial Synthesis Part II: Phase-Transfer Catalyzed Synthesis of Polycarbonate/Polysiloxane Block Copolymers

A phase transfer catalyzed (PTC) method for the preparation of bisphenol-A polycarbonate/polydimethylsiloxane multi-block or segmented copolymers of the structure shown below has been investigated. The synthesis route involves the reaction of a preformed carboxypropyl-terminated polydimethylsiloxane oligomer of various molecular weights with bisphenol-A, base, phosgene, and the PTC. The final copolymer contains a direct [tbnd]Si-C- link between the block structures as compared to the relatively hydrolytically unstable [tbnd]Si-O-C bond discussed previously by the authors and others. A phosgenation “pre-step” to the interfacial reaction was found to be desirable. This procedure involves bubbling phosgene through an anhydrous concentrated solution of the carboxypropyl-terminated polydimethylsiloxane in methylene chloride. Subsequently, a two-phase CH2 Cl2/H2O reaction medium with the phase transfer catalyst is employed in the interfacial step. The phosgenation pre-step is believed to enhance the conversion of carboxyl to acid chloride, which then promotes the efficient incorporation of the polysiloxane into the copolymer. Moreover, anhydride linkages along the chain are reduced to undetectable levels. The copolymers could be of interest as thermoplastic elastomers, elastoplastics, or biomaterials.