EFFECT OF MORPHOLOGY, CROSS-LINK DENSITY, AND MISCIBILITY ON INTERPENETRATING POLYMER NETWORK DAMPING EFFECTIVENESS

The areas under the linear loss modulus versus temperature curves (loss area, LA) and tan-delta versus temperature curves (TA) were evaluated for a number of acrylic, methacrylic, styrenic and butadiene based copolymers and interpenetrating polymer networks, IPNs, as a function of crosslink density and composition, and were compared with values predicted by group contribution analysis. The LAs of the sequential IPNs, cross-poly(n-butyl methacrylate)-inter-cross-polystyrene, were found to exhibit up to 30% larger LAs than the poly(n-butyl metacrylate-stat-styrene) copolymers, which had LAs slightly less than the values predicted from the group contribution analysis. At constant chemical composition (50% n-butyl methacrylate, 50% styrene), LA equals 14.4 GPa . K for the IPN, attributed to a synergistic effect resulting from the IPN's microheterogeneous morphology, as compared with 10.7 GPa . K for the single phase, miscible copolymer. Increases in the LA with increased concentration of polymer network II were also observed for cross-poly(ethyl acrylate)-inter-cross-polystyrene and cross-polybutadiene-inter-cross-polystyrene IPNs. On the other hand, cross-polybutadiene-inter-cross-poly(methyl methacrylate) IPNs had LAs much lower than were predicted by the group contribution analysis, which were attributed to lower miscibility in this system relative to the other systems evaluated. In general, decreased crosslink densities and lower concentrations of network II increased TA. These findings demonstrate how the morphology of a multiphase polymeric material can affect LA and TA, with significant increases in damping capability over the average of the component polymer values.