EFFECTS OF CROSS-LINK DENSITY ON MECHANICAL-PROPERTIES OF HIGH-CLASS TRANSITION-TEMPERATURE POLYCYANURATE NETWORKS

Polycyanurate networks of different architecture were synthesized usin g different curing cycles. Networks with a variable extent of reaction were obtained; the small variation of the cyanate conversion (0.8 to 1) corresponds to a large variation of glass transition temperature (1 50-290 degrees C) and crosslink density. The mechanical behavior at sm all and large deformations and the fracture toughness were examined at room temperature and related to the network structural parameters. To explain the puzzling variation of the yield stress and yield strain w ith the cyanate conversion, recovery experiments were conducted to dis criminate anelastic deformation from plastic deformation. (C) 1997 Joh n Wiley & Sons, Inc.