Calorimetric investigation of polymerization reactions. V. Crosslinked copolymerization of methyl methacrylate with ethylene dimethacrylate

Abstract

Abstract The crosslinked copolymerization of methyl methacrylate with ethylene dimethacrylate (EDMA) in bulk and in toluene has been investigated by differential scanning calorimetry. The appearance of a second peak, in addition to that arising from the gel effect, noted in curves of bulk copolymerization rate (fraction of EDMA m E = 0.20) is explained by the formation of microgels during the copolymerization. With m E = 0.50–1.00, copolymerization proceeds heterogeneously at first, providing opaque microgels, which become transparent polymer in a later stage at a weight fraction of toluene w T ≦ 0.20 and independent polymer particles at w T ≧ 0.30. A diagram is given which illustrates three types of copolymerization depending on initial composition of monomers and toluene. Final conversions for m E ≦ 0.10 agree well with predictions. Copolymerization at m E ≧ 0.20 ceases because of reduction of segmental mobility due to dense network formation in microgel, though the whole system is not yet in glassy state. Data of final conversions in solution copolymerization also support the above mechanism.