New approach in the synthesis of hybrid polymers grafted with polyhedral oligomeric silsesquioxane and their physical and viscoelastic properties

Synthesis, chain characteristics, and time-dependent viscoelastic response of polyhedral oligomeric silsesquioxanes (POSS)-containing hybrid polymers were investigated. Unlike many other reported POSS hybrid copolymers works, the POSS-grafted copolymers used in this study, although having different amounts of POSS attachments, have the same degrees of polymerization and molecular weight distribution. This was accomplished by grafting different amounts of aluminosilsesquioxane onto a previously synthesized, random copolymer of styrene and vinyl-diphenylphosphine oxide, PSP. The coordination bonding between aluminum and phosphine oxide is quantitative, which enables the investigation of physical characteristics and viscoelastic response of polymers as influenced only by the POSS attachments. Similar to other hybrid polymers with covalently bonded POSS, we observed a systemic increase in the characteristic relaxation time of polymers at the terminal zone due to the POSS attachment. Linear viscoelastic response at different temperatures above T-g was studied using the small-strain amplitude oscillatory shear technique. It was found that these POSS-grafted copolymers obey the time-temperature superposition principle. In addition, for isothermal experiments, the linear viscoelastic response obtained for copolymer with varying amounts of POSS attachment were able to be superposed, thus demonstrating that these hybrid copolymers obey the time-POSS content superposition principle. We also examine the effect of POSS-POSS interactions on the long-term viscoelastic response of these copolymers. It was found that copolymers with high POSS attachments exhibit a slow gelation response when held isothermally at temperatures above T-g for extended periods of time, while copolymers with low POSS attachments remain unchanged for the same periods of time. Therefore, this observed gel-like behavior is due to the intrachain POSS-POSS interaction.