PHASE-SEPARATION INDUCED BY A CHAIN POLYMERIZATION - POLYSULFONE-MODIFIED EPOXY ANHYDRIDE SYSTEMS/

The reaction-induced phase separation in a blend of a commercial polys ulfone (PSu) with diepoxide-cyclic anhydride monomers, was studied. Th e diepoxide was based on diglycidylether of bisphenol A ( DGEBA) and t he hardener was methyl tetrahydrophthalic anhydride (MTHPA), used in s toichiometric proportion. Benzyldimethylamine (BDMA) was used as initi ator. PSu had no influence on the polymerization kinetics, the gel con version, and the overall heat of reaction per epoxy equivalent. A kine tic model including initiation, propagation, and termination steps was used to estimate the distribution of linear and branched species in t he first stages of the chain-wise copolymerization. This distribution, together with the PSu distribution, were taken into account in a ther modynamic model of the blend. The interaction parameter was fitted fro m experimental determinations of conversions at the start of phase sep aration, obtained under different conditions. The thermodynamic model was used to explain the complex morphologies developed in materials co ntaining different PSu concentrations as well as their dynamic mechani cal response. The shift in glass transition temperatures was explained by the fractionation of different species during the phase separation process. Phase inversion produced a significant decrease of the elast ic modulus in the glassy state and a thermoplastic-like behavior of th e material in the rubbery region. (C) 1998 John Wiley & Sons, Inc.