SYNTHESIS AND CHARACTERIZATION OF NEW PHOSPHORUS AND OTHER HETEROATOMCONTAINING ARYL CYANATE ESTER MONOMERS AND NETWORKS

Several aromatic dicyanate monomers have been synthesized bearing para linked strong electron withdrawing groups, such as phenylphosphine oxi de, sulfone, and carbonyl. These groups increased the reactivity of th e cyanate functional groups and eliminated the need for curing catalys ts. However, an undesirable decrease in the processing window between the monomer melting point and the onset of cure was also generally obs erved. An arylene ether phenyl phosphine oxide system was designed tha t displayed several attractive characteristics such as a low softening point, a wide processing window, cure with no catalyst, high T-g and high char yield in air, suggesting that these new thermosets might sho w good fire resistance. The dicyanate ester monomers were synthesized in high yield by reacting various bisphenols with cyanogen bromide in the presence of triethylamine. The high reactivity of the cyanate func tional groups required that the cyanation reaction be conducted at tem perature below 0 degrees C in order to prevent imidocarbonate side rea ctions. Proton NMR and FT-IR were used to characterize these monomers. The cyclotrimerization curing process was monitored by the disappeara nce of the carbon-nitrogen triple bond stretch (2270 cm(-1)). An optim al cure schedule was determined and the cured polycyanurate networks w ere characterized by DSC, DMTA, and TGA. Tg values were typically > 25 0 degrees C and 5% weight loss values were observed by TGA in air abov e 400 degrees C. Several of the dicyanate monomers with sufficiently l arge processing windows were cured into single lap shear adhesive bond s onto titanium 6/4 and the measurements are reported herein. (C) 1997 John Wiley & Sons, Inc.