Preparation and properties of poly(tetramethyl‐p‐silphenylene‐siloxane)

Abstract

AbstractImproved methods for the synthesis of p‐bis(dimethylhydroxysilyl)benzene are described. This useful monomer was prepared from p‐bis(dimethylhydrogensilyl)‐benzene which was obtained in 60–70% yields from p‐dibromobenzene and dimethyl chlorosilane by use of an in situ Grignard technique. The great reluctance due to steric factors of the p‐silphenylene‐siloxane configuration to form cyclic structures has been amply demonstrated. The condensation polymerization of p‐bis(dimethylhydroxysilyl)benzene in benzene solution has yielded high molecular weight, crystalline poly‐(tetramethyl‐p‐silphenylene‐siloxanes). The heat of fusion ΔHu of the tetramethyl‐p‐silphenylene‐siloxane was found to be 4350 cal./unit. The modified Staudinger equation relating intrinsic viscosity and weight‐average molecular weight was applicable over a range of 70,000–400,000. These results are summarized in the relationship, [η] = 1.12 × 10−4Mw0.75. Tetramethyl‐p‐silphenylene‐siloxanes were found to be more stable than dimethylsiloxanes both to atmospheric oxidation and degradation through volatile formation in the temperature range 200–305°C.