Aging of silica-filled PDMS/PDPS copolymers in desiccating environments: A DSC and NMR study

The involvement of water in the reinforcing mechanism in silica-filled polydimethylsiloxane (PDMS) based composite systems, potentially leaves the polymer composite susceptible to mechanical property changes when exposed to desiccating environments. We have studied the effects of thermal and chemical desiccation on a silica filled PDMS/PDPS copolymer system by DSC and NMR analysis. Our results show that as the polymer was desiccated, segmental dynamics in the polymer network were reduced significantly and changes in melt heats of fusion and stress relaxation were observed. NMR H-1 relaxation measurements have measured a change in H-1 T-2e of 30% after storage in desiccating environments longer than I year. The experimental data presented argue that the reduced mobility of the PDMS chains in the interfacial domain after desiccation reduced the overall, bulk, motional properties of the polymer, thus causing an effective "stiffening" of the polymer matrix.