VISCOELASTIC AND MORPHOLOGICAL BEHAVIOR OF HYBRID STYRYL-BASED POLYHEDRAL OLIGOMERIC SILSESQUIOXANE (POSS) COPOLYMERS

We report on the viscoelastic behavior of linear thermoplastic nonpola r hybrid inorganic-organic polymers. These materials have been synthes ized through copolymerization of an oligomeric inorganic macromer with 4-methylstyrene where the inorganic portion of the material is a well -defined polyhedral oligosilsesquioxane (POSS), R-7(Si8O12)(CH2CH2C6H4 CH=CH2), with R = c-C6H11 Or c-C5H9 A series of 4-methyl styrene copol ymers with approximately 4, 8, and 16 mol % POSS macromer incorporatio n were investigated. Rheological measurements show that the polymer dy namics are profoundly affected as the percent of POSS increases. In pa rticular, a high-temperature rubbery plateau develops (where a termina l zone is not observed), despite the fact that the parent poly 4-methy lstyrene is unentangled. It is also observed that the thermal properti es are influenced as the percent of POSS incorporation increases, with increases in the glass and decomposition temperatures. The results su ggest that interchain interactions between the massive inorganic group s are responsible for the retardation of polymer chain motion, a mecha nism similar to the ''sticky reptation'' model conceived for hydrogen- bonded elastomers and developed by Leibler et al. [Macromolecules, 24, 4701 (1991)]. Control over the interchain interactions would also giv e rise to the observed increases in glass transition and the establish ment of a rubbery plateau. (C) 1998 John Wiley & Sons, Inc.