Direct and indirect effects of POSS on the molecular mobility of polyurethanes with varying segment Mw

Polyhedral Oligomeric Silsesquioxanne particles were tethered by urethane or urea linkages on the hard segments of polyurethane chains with varying segment Mw. Evidence by imaging, thermal and dielectric techniques suggests that tethering of POSS by urethane bond leads to increase of glass transition temperature by a few degrees due to two mechanisms: the direct POSS-chain interactions and the indirect slowing of dynamics by disruption of microphase separation. The direct mechanism is dominant for the materials with long (high Mw) segments and the indirect becomes more important as the Mw of the segments decreases. High polarity of the urea bond counteracts the effect of disruption of microphase separation and enhances an interfacial glass transition mechanism α′, slower than α, leading to significantly higher apparent glass transition temperatures, despite its small effect on time scales of the individual relaxations.