Necklace-shaped Dimethylsiloxane Polymers Bearing a Polyhedral Oligomeric Silsesquioxane Cage Prepared by Polycondensation and Ring-opening Polymerization

A series of necklace-shaped dimethylsiloxane (DMS) polymers bearing a polyhedral oligomeric silsesquioxane (POSS) cage were synthesized from bifunctional POSS by two different synthetic routes. One-step or two-step polycondensation between POSS and dimethyloligosiloxane dichloride led to necklace polymers with constant chain lengths (n = 2-8). The ring-opening polymerization of octamethylcyclotetrasiloxane (D4) with POSS was also found to provide similar necklace-shaped polymers with dispersed chain lengths of DMS. The thermal properties, decomposition temperature (T-d5%), and glass-transition temperatures (T-g) of the polymers were strongly dependent on DMS chain length. The polymers with dispersed chain lengths gave higher T-g's than the polymers with corresponding constant chain lengths. The highest T-d5% reached 478 degrees C.