Synthesis of branched polymers through graft copolymerization: grafting of isobutylene onto polystyrene by a living cationic process

This report concerns a new approach to the synthesis of graft copolymers of styrene and isobutylene through the use of partly functionalized polystyrene as initiator for the graft polymerization of isobutylene. The initiator is a reactive tertiary ester pendant group attached to a small percentage of the styrene moieties of the starting polystyrene. The coinitiator is BCl₃ which, serving as an activator, helps to initiate the polymerization of isobutylene chains as pendant groups on the starting polystyrene backbone. This graft polymerization process is fast while the competing homopolymerization of isobutylene through BCl₃ is a much slower process and which only occurs to a limited extent. This study confirms the great potential of initiating systems such as BCl₃ for the preparation of graft copolymers with comb-like structures. The system is applicable to other functionalized polymer backbones and may lead to new polymeric materials with interesting properties.