Molecular Dynamics in Cyanate Ester Resin Networks and Model Cyanurate Compounds

Abstract

Molecular dynamics via broad-band dielectric relaxation spectroscopy (DRS) are obtained on a class 3 network-forming system: a generic cyanate ester resin. The potential for in-situ monitoring of the network-forming reaction is explored. The segmental dynamics of the growing network are investigated, and a hitherto unknown secondary relaxation process, β*, is found. This relaxation is distinctly different from the Johari−Goldstein slow β process. Model compounds and conformational strain analysis are used to elucidate the β* relaxation molecular mechanism. The α process in selected cyanate networks was analyzed with the Adam−Gibbs thermodynamics-based relations (AG model). The AG model provides a link between the relaxation time of a cooperatively rearranging domain (CRD) and configurational entropy. The model is explored via DRS and calorimetrically for various network structures. A good agreement is found between independent quantities derived from both techniques when examined in the AG framework. These results lend support to the CRD concept used in the AG model and, more generally, toward the establishment of the heterogeneous view of relaxations in glass-formers.