Aging Effects on Physical Properties of Thiol-Ene Photocured Coatings

摘要

The relationships between sub-T_g aging and physical/mechanical properties of Thiol-Ene photocured coatings are studied in terms of chemical structure and network density. The homogeneous network structure of thiol-enes, having narrow glass transition temperatures, showed characteristic temperature and time dependency on aging behavior which was investigated by enthalpy relaxation with a DSC. Thiol-ene films showed maximum enthalpy relaxation at T_g-10 °C and a linear relationship between the extent of enthalpy relaxation and log of the aging time. Physical property changes of thiol-ene films monitored by pendulum hardness changed as a function of aging time at a specific temperature, which was consistent with the temperature and time dependency of enthalpy relaxation. A multifunctional acrylate (TMPTA) being capable of homopolymerization as well as thiol-acrylate copolymerization was incorporated into the thiol-ene network structure thereby decreasing the network uniformity and affecting the aging behavior. The extent of enthalpy relaxation decreased and the distribution drastically broadened as a function of TMPTA content thus allowing unprecedented control of the sub-T_g aging behavior of thiol-ene based networks by modification and manipulation of the chemical structure.