Mechanical relaxation and microstructure of poly(norbornyl-POSS) copolymers

The mechanical relaxation behavior and microstructure of a series of novel norbornyl-POSS organic-inorganic copolymers have been investigated. We have examined the influence on physical properties of both the weight, fraction of POSS-norbornyl monomer and the corner group composition. POSS. refers t o the polyhedral oligomeric silsesquioxane inorganic/organic macromer, whic h is composed of an inorganic Si8O12 spherical core surrounded by seven ine rt organic corner groups and one reactive norbornyl moiety, It was observed that POSS copolymerization enhances the cr-relaxation temperature, T-alpha , in proportion to the weight fraction of the POSS-norbornyl comonomer. Int erestingly, however, the magnitude of this this dependence is larger for th e POSS-norbornyl comonomer possessing cyclohexyl corner groups (CyPOSS) tha n for the copolymer with cyclopentyl corner groups (CpPOSS). Although POSS copolymerization yields only slight enhancement of the room temperature sto rage modulus, at temperatures lower than a strong mechanical relaxation, id entified as a beta-relaxation, and near T = -78 degrees C, there isa signif icant POSS reinforcement of the storage modulus, The position of the beta r elaxation observed in the CyPOSS series of copolymers is Independent of POS S weight fraction, and the frequency dependence of this peak position yield s the activation energy, Delta H-beta = 14.7 (liberation of motion of the c yclohexyl corner groups). A similar effect is observed, to some extent, for the CpPOSS copolymers, although only part of Be relaxation is observed. X- rag scattering shows that, the CyPOSS copolymerization preserves the amorph ous character of the polynorbornene homopolymer but CpPOSS copolymerization leads to significant ordering of the POSS macromers.