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 (Td5%), and glass-transition temperatures (Tg) of the polymers were strongly dependent on DMS chain length. The polymers with dispersed chain lengths gave higher Tg’s than the polymers with corresponding constant chain lengths. The highest Td5% reached 478 °C.

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