Physical and chemical modifications of thiol-ene networks to control activation energy of enthalpy relaxation

Gold nanoparticles and multi-functional acrylate (TMPTA) were incorporated into a photopolymerized thiol-ene (TMPMP-APE) network as a physical and chemical approach to intentionally control sub-Tg aging. The degree of the restriction effect was evaluated by differential cooling rate measurements allowing the quantification of the apparent activation energy for enthalpy relaxation (Δh*) upon sub-Tg aging. Incorporation of gold nanoparticles (0.01 to 1 wt%) into the TMPMP-APE network increased Tg and decreased ΔCp at Tg due to molecular mobility restrictions. The extent of enthalpy relaxation and apparent activation energy for enthalpy relaxation (Δh*) clearly indicated the significant restrictive effect of the gold nanoparticles on the molecular mobility in the thiol-ene network. A TMPMP-APE-TMPTA ternary system was investigated in order to correlate Δh* and network uniformity as a chemical approach. TMPTA, being capable of homopolymerization as well as TMPMP-TMPTA copolymerization, was incorporated into a TMPMP-APE network structure, thereby decreasing the network uniformity and significantly affecting the sub-Tg aging. The extent of enthalpy relaxation decreased and the distribution was drastically broadened as a function of TMPTA content due to molecular mobility restrictions, which were also quantified by measuring values for the apparent enthalpy relaxation activation energy (Δh*).