New Insights into Structure - Property Relationships in Thermosetting Polymers from

Studies of the physical properties of the co-cured networks formed from three similar dicyanate ester monomers revealed a number of unexpected variations from simple linear mixing rules. These variations shed light on important synergistic effects in co-cured thermosetting networks and their possible causes. The monomers utilized were the dicyanate esters of Bisphenol A (BADCy), Bisphenol E (LECy), and the silicon-containing analog of Bisphenol A (SiMCy). The most important of the synergistic effects was a decrease of approx. 25% in moisture uptake seen only in co-networks of LECy and SiMCy. For all other systems, a clear relationship between moisture uptake and the number density of cyanurate rings was observed. This relationship generally applies to many types of cyanate esters and gives an indication of the importance of specific sites (as opposed to free volume alone) in moisture uptake. Numerous additional examples of non-linear mixing relations were observed in the glass transition temperature, density, and thermochemical stability of fully cured networks. Interestingly, the most widespread deviations from linear behavior were observed for co-networks of SiMCy and