Effect of polymeric additives on properties of glass-bisphenol A dicyanatelaminate composites

The polycyanurate network matrix derived from the thermal, dibutyl tin dila urate catalyzed polymerization of bisphenol A dicyanate was modified in the ir glass-laminate composites with different linear polymeric additives bear ing pendant phenol, cyanate, and epoxy functions. The mechanical properties and fracture energy for delamination of the glass-laminate composites were estimated as functions of the backbone structure and concentration of the various additives. The effect of altering the nature or concentration of th e functional group for a given backbone structure of the additive was exami ned in some cases. Except for the epoxy functional acrylic polymer, all oth er systems adversely affected the fracture energy for delamination of the c omposites due to either plasticization or embrittlement of the matrix. With the exception of the styrene-hydroxyphenyl maleimide (SPM) copolymer, the other modifiers impaired the mechanical properties and adversely affected t he thermomechanical profile of the composites. In the cases of the phenol f unctional acrylic polymer and its cyanate derivative, plasticization of the matrix by the partly phase-separated additive, which eased the fiber debon ding, appears to be responsible for the impairment of the mechanical proper ties. The high glass transition temperature SPM copolymer enhanced the resi n-reinforcement interaction through dipolar interactions induced by the hyd roxyl groups, which resulted in amelioration of the mechanical properties. However, its possible coreaction and formation of a brittle, homogeneous ph ase with the polycyanurate was conducive for poor damage tolerance. The SEM analysis of the fractured composites showed that in the elastomers fiber d ebonding is the major cause for delamination. Although the presence of SPM led to a stronger interphase, failure occurred either in the brittle matrix or through fiber breakage. (C) 2000 John Wiley & Sons, Inc.