Effect of POSS on thermomechanical properties of epoxy–POSS nanocomposites

[Display omitted] ► The epoxy–POSS nanocomposites with the controlled structure were synthesized. ► Physical crosslinking via POSS domains occurs during epoxy network formation. ► Mechanical properties were interpreted by using theoretical approaches. ► Relationships between structure and thermomechanical properties of nanocomposites. The epoxy–POSS hybrid networks with POSS bound as pendant cages or with untethered POSS dispersed in the matrix were prepared and their structure was controlled. Formation of the hybrid network was followed by chemorheology. In situ development of physical crosslinks in the pregel stage of the network build-up was observed in case of the hybrids with tethered POSS. The complex effect of POSS on mechanical properties is manifested by either increase or decrease in rubbery modulus of different hybrids. This behavior reflects (a) reinforcement due to POSS hard aggregates, (b) diminishing of crosslinking density of the epoxy network by tethered monofunctional POSS and (c) physical crosslinking via POSS domains. Theories of network formation and rubbery elasticity as well as the model of mechanical behavior of particulate composites were applied to interpret the mechanical properties of the hybrids.