Effect of intramolecular cycles on the polycyclotrimerization of aromatic dicyanates

The gel conversions (α_gel) for the polycyclotrimerization of aromatic dicyanates are significantly higher than the classical mean-field value of 0.5. The reasons for the higher gel conversion, which is consistent with all experimental results of different structures of monomers, were inductively attributed to the accessibility effect of the functional group and the substitution effect, as well as the effect of the intramolecular cyclization. Nevertheless, the former two effects on the gel conversion can be quantitatively represented in terms of the extent of the intramolecular cyclization. Some theoretical expressions (including gel conversion and crosslink density with respect to the conversion) were derived by use of the recursive method with due consideration of the intramolecular cyclization. These expressions (with only one experimental parameter, α_gel) were found to be effective in describing gel fraction–conversion data for various polycyanurates. A dramatic change in the product value of ΔC_p · T_g was also found in the vicinity of the gel point for all different structures of aromatic dicyanate systems. The dramatic change in ΔC_p · T_g occurs at the gel point rather than the expected mean-field gel conversion of 0.5, presumably due to the intramolecular cyclization. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 1927–1938, 1999