Role of Nonbond Interactions in the Glass Transition of Novolac-Type Phenolic Resin: A Molecular Dynamics Study

Nonbond interactions, such as hydrogen bonds and π–π/p-π interactions, have a decisive effect on the physical properties of phenolic-rich polymers, such as the novolac-type phenolic resins. To study the influence of nonbond interactions on the glass transition temperature (T_g) of novolac resins, both the molecular dynamics and experimental approaches were applied. The results show that, compared with the o-p′ type novolac, the o-o′ type novolac models have relatively lower gyration radiuses and higher T_g values because more intramolecular hydrogen bonds can be formed in the o-o′ type novolac models. As there are fewer hydrogen bonds formed in o-p′ type novolac, the π–π and p-π interactions, which decrease with the degree of polymerization and temperature, strongly influence the glass transition of o-p′ type novolac. These results provide a new perspective on the structural-property relationship of phenolic resin.