Amorphous phenolphthalein-based poly(arylene ether)-modified cyanate ester networks: Effect of thermal cure cycle on morphology and toughenability

Reactive functional thermoplastic poly(arylene ether) toughness modifiers were demonstrated to enhance toughness of brittle thermosetting cyanate ester networks and also allowed retention of a highly desirable stability to solvent stress cracking and a moderately high modulus. Careful control of the heterophase morphological structure was necessary to achieve significant toughening. In contrast to the well-defined morphologies of the reactive thermoplastic-modified networks, the use of nonreactive simple physical blend modifiers of the same molecular weight and backbone chemistry produced a macrophase separation and no apparent control over the sizes of the phase-separated domains. Macrophase-separated morphologies are inherently process-sensitive and less desirable from the point of performance control and prediction. Generation of controlled microphase-separated morphologies can be achieved by systematically varying thermal cure cycles in the case of the reactive thermoplastic-modified systems. Such a cure cycle dependence of the morphology was particularly demonstrated for the case of the 25 wt % 15,000 (M(n)) (15K) phenolphthalein-based hydroxy-functionalized poly(arylene ether sulfone) (PPH-PSF-OH)-modified networks. Morphologies that exhibit finer textures of the phase separated domains usually result in lower fracture toughness values. (C) 1997 John Wiley & Sons, Inc.