Photocured Simultaneous and Sequential PDMS/PMMA Interpenetrating Polymer Networks

Photocured interpenetrating polymer networks (IPNs) of PDMS and PMMA were synthesized through a sequential route to form semi-IPNs and a simultaneous route to form graft IPNs. Experiments were designed to understand the effect of network architecture and PMMA concentration on IPN microstructure, thermal properties, mechanical properties, and chemical structure. At PMMA concentrations above 10 wt %, the microstructure in both IPN architectures consisted of a dispersed PMMA phase in a PDMS continuous phase, where the domain size and shape were found to depend on both the synthetic route and the PMMA concentration. The PMMA glass transition temperature in sequential IPNs was nearly unaffected by PMMA concentration, indicating that the PMMA and PDMS phases were poorly mixed. In contrast, the PMMA glass transition region in the simultaneous IPNs was complex. This was interpreted to indicate the presence of both mixed PDMS/PMMA and pure PMMA phases, the ratio of which depends on PMMA concentration. PeakForce Tapping was used to directly determine how differences in the extent of mixing impact the mechanical properties of the dispersed phases. In the simultaneous IPNs, the number of cross-links between the PDMS and PMMA networks was found to increase as a function of PMMA concentration. The PMMA molecular weight distribution remained constant with PMMA concentration in the sequential IPNs, whereas increasing PMMA concentration in the simultaneous IPNs substantially increased polydispersity and led to a bimodal molecular weight distribution. PMMA concentration also appears to play a minor role in determining PMMA stereoregularity in the simultaneous IPNs. Overall, this study demonstrates how structure/process relationships can be used to control properties in these hybrid elastomers.