PHYSICAL AND MECHANICAL CHARACTERIZATION OF NEAR-ZERO SHRINKAGE POLYBENZOXAZINES

A new class of phenolic-like thermosetting resins has been developed t hat is based on the ring-opening polymerization of a benzoxazine precu rsor. These new materials were developed to combine the thermal proper ties and flame retardance of phenolics with the mechanical performance and molecular design flexibility of advanced epoxy systems. The polyb enzoxazines overcome many of the traditional shortcomings of conventio nal novolak and resole-type phenolic resins, while retaining their ben efits. The physical and mechanical properties of these new polybenzoxa zines are investigated and are shown to compare very favorably with th ose of conventional phenolic and epoxy resins. The ring-opening polyme rization of these new materials occurs with either near-zero shrinkage or even a slight expansion upon cure. Dynamic mechanical analysis rev eals that these candidates for composite applications possess high mod uli and glass transition temperatures, but low crosslink densities. Lo ngterm immersion studies indicate that these materials have a low rate of water absorption and low saturation content. Impact, tensile, and flexural properties are also studied. Results of the dielectric analys is on these polybenzoxazines demonstrate the suitability of these mate rials for electrical applications. (C) 1996 John Wiley & Sons, Inc.