PREPARATION OF ASYMMETRIC 3-ARM POLYBUTADIENE AND POLYSTYRENE STARS

The synthesis of three-armed polybutadiene and polystyrene stars is described for the case where one of the three arms differs in molecular weight from the remaining two. The preparative approach involves the reaction of methyltrichlorosilane with the chain end active centers under conditions unfavorable to chain coupling or linking, i. e. , the synthesis of linear doublet chains or three-arm stars. Some observations regarding thermal-induced post-polymerization side reactions that distort the near-monodisperse nature of the molecular weight distributions obtainable for polybutadiene are described. Preparative conditions must be selected to avoid such side reactions if 'model' branched polybutadienes are required.