Viscoelastic and morphological behavior of hybrid styryl-based polyhedral oligomeric silsesquioxane (POSS) copolymers

We report on the viscoelastic behavior of linear thermoplastic nonpolar hybrid inorganic-organic polymers. These materials have been synthesized through copolymerization of an oligomeric inorganic macromer with 4-methylstyrene where the inorganic portion of the material is a well-defined polyhedral oligosilsesquioxane (POSS), R₇(Si₈O₁₂)(CH₂CH₂C ₆H₄CH=CH₂), with R = c-C₆H₁₁. or c-C₅H₉. A series of 4-methyl styrene copolymers with approximately 4, 8, and 16 mol % POSS macromer incorporation were investigated. Rheological measurements show that the polymer dynamics are profoundly affected as the percent of POSS increases. In particular a high-temperature rubbery plateau develops (where a terminal zone is not observed) despite the fact that the parent poly 4-methylstyrene is unentangled. It is also observed that the thermal properties are influenced as the percent of POSS incorporation increases with increases in the glass and decomposition temperatures. The results suggest that interchain interactions between the massive inorganic groups are responsible for the retardation of polymer chain motion, a mechanism 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 give rise to the observed increases in glass transition and the establishment of a rubbery plateau.