Stress reduction in phase‐separated, cross‐linked networks: Influence of phase structure and kinetics of reaction

A mechanism for polymerization shrinkage and stress reduction was developed for heterogeneous networks formed through ambient, photo‐initiated polymerization‐induced phase separation (PIPS). The material system used consists of a bulk homopolymer matrix of triethylene glycol dimethacrylate (TEGDMA) modified with one of three nonreactive, linear prepolymers (poly‐methyl, poly‐ethyl, and poly‐butyl methacrylate). At higher prepolymer loading levels (10–20 wt %), an enhanced reduction in both shrinkage and polymerization stress is observed. The onset of gelation in these materials is delayed to a higher degree of methacrylate conversion (∼15–25%), providing more time for phase structure evolution by thermodynamically driven monomer diffusion between immiscible phases prior to network macro‐gelation. The resulting phase structure was probed by introducing a fluorescently tagged prepolymer into the matrix. The phase structure evolves from a dispersion of prepolymer at low loading levels to a fully co‐continuous heterogeneous network at higher loadings. The bulk modulus in phase‐separated networks is equivalent or greater than that of poly(TEGDMA), despite a reduced polymerization rate and cross‐link density in the prepolymer‐rich domains. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131 , 40879.