A study on the effects of network interconnection on the topological, physical, thermomechanical, and mechanical properties of epoxy-methacrylate interpenetrating polymer networks

Interconnected interpenetrating polymer networks (IPNs) formed through the incorporation of small-size dual-functional interlinkers, such as glycidyl methacrylate, have demonstrated improved material properties over simple IPNs. Whether increased crosslink density or network interconnection was the main contributing factor to the improvements in IPN properties is unknown. In this work, 4-glycidyl ether-4′-glycidyl methacrylate of bisphenol A (BPA-GE-GMA) was used to interconnect the IPNs of diglycidyl ether of bisphenol A (DGEBA) and bisphenol A glycidyl dimethacrylate (Bis-GMA). It was hypothesized that the use of BPA-GE-GMA would not alter the crosslink density of the IPNs from dual-cure epoxy-methacrylate formulations containing DGEBA, BPA-GE-GMA, and Bis-GMA. The amount of BPA-GE-GMA was varied to study the effects of network interconnection on the properties of interconnected IPNs. Our results revealed that the use of BPA-GE-GMA led to a shift in material properties away from those of the methacrylate system and towards those of the epoxy system, that is, reduced cure shrinkage, decreased compressive modulus, higher glass transition temperature (T_g), and enhanced fracture toughness property. However, it was discovered that the effective crosslink density increased with higher BPA-GE-GMA content. This increase can be attributed to the ability of BPA-GE-GMA as a mono-methacrylate to facilitate better methacrylate network formation. As a result, the effects of network interconnection and crosslink density were not fully decoupled. Nevertheless, since the crosslink density factor already contributes to the observed differences in material properties, it is likely that the effects of network interconnection are minimal.