CYCLOTRIMERIZATION REACTIVITIES OF MONO-FUNCTIONAL AND DIFUNCTIONAL CYANATES

The influence of substituents of several mono- and difunctional cyanat es on their cyclotrimerization behaviour has been studied by several m ethods. Shifts of gel point and gel fractions at full conversion in de pendence on the substituent were detected for coreactions of a dicyana te with monofunctional cyanates. Critical fractions of monocyanate gro ups in the range of 50 mol-% for the absence of gelation were measured and could be described quantitatively by a model that is based on rea ction kinetics and network statistics. Reactivity differences in depen dence on substituents are also reflected in the distribution of homo- and mixed trimers at full conversion of pairs of different monofunctio nal cyanates as measured by high-performance liquid chromatography (HP LC). This distribution follows a simple binomial scheme for cyanates w ith equal reactivity, whereas remarkable deviations occur, if one of t he monomers reacts faster than the other. Besides, a qualitative react ivity gradation of the used cyanates was found on the basis of differe ntial scanning calorimetry (DSC) peak temperatures, where the reaction of each cyanate was catalyzed by the same amount of a certain phenol. Finally, the shift of the OH band of several phenols caused by associ ation with cyanate groups, measured by FTIR, was related to the data o btained from gelation, trimer distribution and DSC experiments to esta blish an easy and reproducible method for comparing the reactivity of cyanate monomers.