| The hydroxyl-terminated and carboxyl-terminated PU-prepolymer were prepared and cured respectively with PF. The molecule structures of two composite systems were characterized by means of FT-IR, and cured-sample morphologies were analyzed by SEM. By means of the measurement of properties of PF, impact strength, volume shrinkage and thermal stability of PF/PU composite, effect of PU on PF has been investigated and the toughening differentials have been compared , then two kinds of toughening mechanisms have been discussed. The results show that :(1) The cure is accelerated by increasing the usage of cure catalyst and cure temperature, but cure effect is bad with too fast speed, so 3.5% cure catalyst and 80℃ cure temperature were cheese. (2) The results of impact experiments show that impact strength of PF is improved and improvement lever is related to WPU; but effect of carboxyl-terminated PU-prepolymer is better, that is to say the interpenetrating networks have priority at toughening of thermosetting resin. (3) volume shrinkage of composite decreases greatly with WPU　increasing, even can arrive a negative number, but thermal stability is still good.(4)toughening mechanism is that :the formation of high molecular linear amino formate construct is the toughening reason; hydroxyl-terminated PU-prepolymer and PF react to produce chemical bond effect which participate cure; carboxyl-terminated PU-prepolymer and PF form semi-IPN which make toughened PF occur maximum.
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