Free Volume, Transport, and Physical Properties of n-Alkyl Derivatized Thiol−Ene Networks: Chain Length Effect

Abstract

The free volume, transport, and physical properties of a series of n-alkyl derivatized thiol−ene networks are reported. Derivatized thiol monomers were prepared via a nucleophile-catalyzed thio-Michael addition reaction of multifunctional thiols to n-alkyl acrylates ranging from n = 1 to n = 16 in length. Using UV-initiated photopolymerization, cross-linked networks were fabricated from these systematically modified thiol monomers. Each network consisted of the same molar concentration of alkyl chains. Both the thio-Michael reactions and the network photopolymerizations reached high conversion regardless of n-alkyl length, which is typical of the thiol−ene click reaction. The incorporation of alkyl chains led to the formation of new networks with markedly loose packing as probed by density measurements. The density decreased by 11% as n increased from 1 to 16. It is believed that the alkyl chains acted as spacers or pillars which expanded the cross-linked network scaffold increasing the free volume. The f...