Reaction Rate Acceleration and Tg Depression of Polycyanurate Under Nanopore Confinement

摘要

Materials under nanopore confinement show changes in reaction rate and T_g as pore diameter decreases. Previous work from our laboratory on the trimerization of cyanate esters found that the reaction kinetics were faster for a mono-functional reactant compared to a di-functional monomer, whereas the T_g depression was greater for the crosslinked product of the latter compared to the low molecular weight trimer of the former. Thus, the origin of the changes in nanoconfined reaction rates differs from those that govern changes in the T_g. The purpose of this study is to further investigate the nanoconfinement effects for the cyanate ester trimerization reaction using a mixture of monocyanate and dicyanate esters that produce an uncrosslinked polycyanurate (M_w = 11000 g/mol, PDI = 1.98). The nanopore-confined material is synthesized in-situ and the reaction kinetics are followed by differential scanning calorimetry (DSC); after the reaction, the T_g values of the nanoconfmed polymer are also measured by DSC. An acceleration factor of 13 ± 2.3 and a T_g depression of 38 °C are observed for the material confined in the smallest 8.1 nm-diameter pores; although the T_g depression is between those of the trimer and polycyanurate, the acceleration of the reaction rate is lower, consistent with the reaction acceleration arising from packing effects and the T_g depression arising from intrinsic size effects.