Molecular dynamics in polyurethane foams chemically reinforced with POSS

In this work, we report on the thermal and thermomechanical properties of rigid PU foams modified with POSS moieties, paying special attention to molecular dynamics of these systems. 1,2-Propanediolisobutyl POSS (PHI-POSS) are used as pendent groups and octa(3-hydroxy-3-methylbutyldimethylsiloxy) POSS (OCTA-POSS) serve as chemical crosslinks. DSC reveals an initial slowing down of the segmental dynamics for small loadings (5 wt%) of both POSS moieties, followed by an acceleration, probably due to changes in the topology of the PU network and the morphology of the foam. A low-temperature mechanical relaxation is observed by DMA and is attributed tentatively to a local β relaxation, much similar to that observed in hyperbranched polyurethanes.