Structure-Property Studies on a Series of Polycarbonate-Polydimethylsiloxane Block Copolymers

Block copolymers composed of hard and soft segments form an interesting class of materials ranging from thermoplastics to thermoplastic elastomers depending on their composition and/or the size of segments. These materials have attracted much attention in the past decade because by careful tailoring, polymers of desired properties can be obtained. Yet they are thermoplastic in nature and can be processed and even reprocessed thermally. Among the common elastomers that can be used as the soft segment in a block copolymer, polydimethyl-siloxane is of special interest due to its great thermal stability at elevated temperatures and high flexibility at low temperatures. Block copolymers containing polydimethylsiloxane as the soft segment and various thermoplastics such as poly(α-methylstyrene), polystyrene, and polysulfone, etc., as the hard segment, have been synthesized and studied. A group of randomly alternating block copolymers of bisphenol-A polycarbonate and polydimethylsiloxane have also been prepared by in situ polymerization of dichloro-terminated siloxane oligomers and bisphenol-A and phosgene. The properties of these block copolymers as well as those of the others have been discussed to some extent in a general review. This work reports the results of a study on the structure-property relationship of a series of perfectly alternating block copolymers of bisphenol-A polycarbonate and polydimethylsiloxane synthesized via different routes. They were prepared by silylamine-hydroxyl reaction. Slightly less than the stoichiometric quantity of siloxane oligomers was incrementally added to a hydrated solution of the polycarbonate in refluxing chlorobenzene. The reaction can be represented by the simple scheme: