Synthesis and characterization of new dicyanate monomers. A way to obtain fully aromatic crosslinked poly(ether ketone)s

Several aromatic mono- and dicyanate monomers bearing ether and ketone grou ps in the main chain have been synthesized through high-yield reactions wid ely used in organic chemistry. FT-IR and NMR were used to characterize thes e monomers and the intermediate products. The cyclotrimerization reaction w as studied by DSC in monocyanate models, and the enthalpy of the reaction w as determined. The value obtained was approximately 95 kJ/mol of cyanate ir respective of the substituent and symmetry of the substitution. For short d icyanates, cyclotrimerization did not reach completion, and for long dicyan ates, the enthalpy of reaction could not be evaluated with accuracy. The re sulting cured polycyanurates networks, due to the selectivity of the cyclot rimerization reaction, could be considered as true fully aromatic crosslink ed poly(ether ketone)s with controlled structure. T-g values of the network s were above 180 degrees C. The higher values were found for shorter dicyan ates and for monomers with para substitution. The 1% and 5% weight loss val ues in nitrogen were above 310 and 380 degrees C, respectively, with char y ields in the range 50-60%. (C) 1999 John Wiley & Sons, Inc.