Tg and reactivity at the nanoscale

Nanoscale constraint is known to have a significant impact on the thermal properties of materials. In this work, differential scanning calorimetry (DSC) is used to investigate the depression in the glass transition temperature (T-g) and the reactivity of a monofunctional and of a difunctional cyanate ester Cured under nanoscale constraint. Both reactants undergo trimerization, but the former forms a small molecular-weight compound, whereas the latter forms a polycyanurate network material. A T-g depresssion is observed for both the reactants and their products; the magnitude of the depression seems to be related to the size of the molecule being confined relative to the confinement size. The trimerization reaction is accelerated relative to the bulk when the reactants are confined in nanopores. This is clearly observed by a shift in the reaction exotherms to lower temperatures for dynamic temperature scans. Quantification of the acceleration is accomplished by converting the dynamic temperature scan data to conversion versus time data assuming constant activation energy. The results are consistent with acceleration factors obtained from isothermal cure studies, but the dynamic data is considerably easier to obtain. (C) 2009 Elsevier B.V. All rights reserved.