In this paper, the prepolymer was prepared by addition reaction of diisocyanate to polymer blend which was composed of liquid hydroxyl-terminated polybutadiene (HT-PB) and unsaturated polyester, and was cured with vinylmonomer and diol. The composite which was a cured mixture consisting of unsaturated polyester and HT-PB with vinylmonomer and diol showed undesirable mechanical properties because the solubility of unsaturated polyester for HT-PB was bad.
Therefore, the prepolymer was prepared by addition reaction of diisocyanate to polymer blend obtained by mixing small amounts of unsaturated polyester into HT-PB (HT-PB/unsaturated polyester =75/25), and the prepolymer was cured with diol and vinymonomer [Styrene or methylmethacrylate (MMA)].
As the result, it was made clear that the crosslinked composite was reinfored by a highly heat-dependent hard block consisting of unsaturated polyester and vinylmonomer and the morphology of crosslinked polymer was composed of the domain of unsaturated polyester-vinylmonomer copolymer and the domain of homopolymer which were dispersed in rubber matrix.
Comparing styrene with MMA as crosslinking agent, the mechanical properties of composite cured with styrene turned out better than MMA. It could be considered that the result described above was attributable to the rate of homopolymerization of vinylmonomer and the rate of copolymerization of vinylmonomer and unsaturated polyester.

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The prepolymer was prepared by additive reaction of diisocyanate to polymer blend which was composed of liquid hydroxyl-terminated polybutadiene (HT-PB) and liquid hydroxyl-terminated 1, 2-polybutadiene (1, 2-PB). The prepolymer was crosslinked with vinylmonomer and diol. The physical property and morphology of crosslinking polymer were examined for mechanical property, swelling, dynamic visco-elasticity, and electron microscopic observation.
From these results, it could be seen that the crosslinked polymer had high toughness and broad elasticity, a hard block depending upon heat to a great extent was formd, and the domain was dispersed in rubber matrix of crosslinked polymer.
Comparing addition system of methylmethacrylate (MMA) with that of styrene, the hardness, tensile strength, and 100% modulus of MMA system were superior to those of styrene system, but elongation of MMA system was inferior to that of styrene system. It was concluded that the characteristics of composites obtained on the addition system of MMA resulted from the formation of continuous phase having high network density, and also that high elongation of elastomer obtained on addition system of styrene was attributable to plasticizing effect of polystyrene block and good domain structure.

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