A low-molar-mass, hydroxyl-terminated polyether [polypropylene glycol/poly(ethylene glycol) copolymer (POPE)] was functionalized with isocyanate groups and used to improve the impact resistance of a diglycidyl ether of bisphenol A based epoxy resin cured with triethylene tetramine (TETA). The effect of polyetherbased modifiers (with and without NCO groups) on the curing rate of the epoxy/TETA system was investigated with rheological techniques. The NCO-functionalized polyether reduced the gel time, and this indicated an accelerating effect of the curing process. In addition, a significant improvement in the impact resistance was observed with only a slightly detrimental effect on the stiffness and mechanical strength. Scanning electron microscopy of the corresponding epoxy network revealed a homogeneous morphology with no phase separation. The miscibility of NCO-modified POPE and the epoxy resin was also confirmed with atomic force microscopy. The glass-transition temperature of the epoxy networks was also investigated with dynamic mechanical techniques.

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Low molar mass hydroxyl‐terminated polyester was functionalized with isocyanate groups (NCO) and used to improve the impact resistance of epoxy resin (ER) cured with triethylene tetramine (TETA). The effect of polyester‐based modifiers (with or without NCO groups) on the curing rate of epoxy/TETA system was investigated by rheological techniques. It was found that the functionalized polyester decreased the gel time, indicating an accelerating effect of the curing process. In addition, significant improvement in impact resistance of the epoxy network was achieved, with low detrimental effect on the glass transition temperature and stiffness. The modified epoxy systems did not present phase‐separated morphology discernible by scanning electron microscopy, even after the curing process. The glass transition temperature of the epoxy networks was also investigated by dynamic‐mechanical analysis. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers

Copolímero em bloco de resina epoxídica modificada com polibutadieno líquido, funcionalizado com grupos carboxila foi preparado e o material reticulado correspondente foi comparado com resina epoxídica pura ou sua mistura física com polibutadieno líquido hidroxilado. A resina modificada com polibutadieno líquido carboxilado apresentou resistência ao impacto superior e melhor desempenho mecânico em termos de propriedades de tensão e de flexão. Essa melhora foi atribuída à presença de partículas de borracha homogeneamente dispersas dentro da matriz epoxídica. Esse sistema modificado também resultou em melhora das propriedades mecânicas dos compósitos correspondentes com fibra de carbono. As propriedades superiores foram atribuídas a uma melhor interação fibra-matriz, evidenciada por microscopia eletrônica de varredura.Epoxy resin networks have been modified with block copolymer of polybutadiene and bisphenol A diglycidyl ether (DGEBA)-based on epoxy resin. The epoxy resin modified with carboxyl-terminated polybutadiene presented improved impact resistance and outstanding mechanical performance in terms of flexural and tensile properties because of the presence of rubber particles homogeneously dispersed inside the epoxy matrix. This modified system also resulted in an improvement of mechanical properties of the corresponding carbon fiber based composites. The outstanding properties were attributed to a better interaction fiber-matrix, as indicated by SEM micrographs.