title: Stress reduction in phase-separated, cross-linked networks: influence of phase structure and kinetics of reaction.
abstract: A mechanism for polymerization shrinkage and stress reduction was developed for heterogeneous networks formed via 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 non-reactive, linear prepolymers (poly-methyl, ethyl and 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.
authors.affiliation: Department of Chemical and Biological Engineering, University of Colorado, Boulder, CO 80309, USA.
authors.forename: Caroline R
authors.initials: CR
authors.lastname: Szczepanski
authors.affiliation: Department of Chemical and Biological Engineering, University of Colorado, Boulder, CO 80309, USA ; Biomaterial Research Center, School of Dental Medicine, University of Colorado, Aurora, CO 80045, USA.
authors.forename: Jeffrey W
authors.initials: JW
authors.lastname: Stansbury