PHOTOCURED POLYMER NETWORKS BASED ON MULTIFUNCTIONAL BETA-KETOESTERS AND ACRYLATES

The objects of this study are highly crosslinked networks. The base-ca talyzed Michael reaction of beta-ketoesters with vinyl groups of the p entaerythritol tetra-acrylate (PETA) was used for a step grow formatio n of the crosslinked polymer in dark. The nonreacted vinyl groups and vinyl monomer were built up to the network structure by photopolymeriz ation in the second step of synthesis. An analysis of crosslinked poly mers shows that the long spacer between beta-ketoester groups in propy lenglycol-425-diacetoacetate (PGDAA) favors an extent of reaction comp ared to pentaerythritol tetrakis (acetoacetate) (PETAA). The excess of vinyl monomers added to polymerization batch functions in the first s tep of the synthesis as a reactive solvent [triethylene glycol dimetha crylate (TEGDMA); PETA]. The dissolution of reactants has a positive e ffect on homogeneity, conversion, and crosslink density of prepared ne tworks. The consumption of reactive groups in a course of the network formation, the crosslink density, and dynamic mechanical properties of the prepared networks were determined from Fourier transform infrared (FTIR) spectroscopy, differential scanning calorimetry (DSC), sol-gel analysis, dynamic testing, and stress-strain dependencies. The dynami c testing indicates that the networks synthesized in two steps from ba tches containing an excess of vinyl monomer consist from two highly cr osslinked phases interpenetrating each other. (C) 1997 John Wiley & So ns, Inc.