Ester-free thiol-X resins: new materials with enhanced mechanical behavior and solvent resistance

Abstract

A series of thiol-Michael and radical thiol-ene network polymers were successfully prepared from ester-free as well as ester-containing monomer formulations. Polymerization reaction rates, dynamic mechanical analysis, and solvent resistance experiments were performed and compared between compositions with varied ester loading. The incorporation of ester-free alkyl thiol, vinyl sulfone and allylic monomers significantly improved the mechanical properties when compared with commercial, mercaptopropionate-based thiol-ene or thiol-Michael networks. For polymers with no hydrolytically degradable esters, glass transition temperatures (Tg's) as high as 100 °C were achieved. Importantly, solvent resistance tests demonstrated enhanced stability of ester-free formulations over PETMP-based polymers, especially in concentrated basic solutions. Kinetic analysis showed that glassy step-growth polymers are readily formed at ambient conditions with conversions reaching 80% and higher.

Ester-free thiol–ene dental restoratives—Part A: Resin development

“…Esters are known to degrade through hydrolysis catalyzed by acids or bases as well as various enzymatic cleavage processes. Also, by having affinity to water and being able to associate with water through hydrogen bonding, ester-containing networks usually swell quite considerably [30]. As shown in Table 3, the BisGMA/TEGDMA polymer has a significantly higher degree of water sorption and solubility compared to any of the thiol-ene systems tested.…”

“…All chemicals were used as received. SiTSH and 1,3,5-tris-(3-mercaptopropyl)-1,3,5-triazine-2,4,6-trione (TTTSH) were synthesized according to a previously reported procedure [30,32,33]. The tetra-allyl monomer (TENE) was synthesized upon treatment of an alcohol with an isocyanate to form urethane linkages [34].…”

“…These materials also demonstrated extraordinary stability in acidic and basic solutions [30]. Based on another study, we found that introducing a vinyl sulfone group as an ene moiety significantly enhanced the mechanical properties of the material [31].…”

Ester-free thiol–ene dental restoratives—Part B: Composite development

“…Prior to implementation and as described later, these fillers were subsequently functionalized with thiol and/or allyl groups for inclusion and copolymerization in the composite. Tetra(2-mercaptoethyl)silane (SiTSH) and the urethane-based tetraallylether monomer (TENE) were both synthesized according to previously reported procedures [29,33,35]. The structures of DVS-activated thiol monomers as well as the other monomers and solvents used are detailed elsewhere [34].…”

“…Recently, it has been shown that the mechanics of the flexible step-growth polymer backbone containing soft sulfide linkages can be enhanced significantly in poly(thioether) networks by eliminating the presence of esters [30–33]. Achieving that, and combining other benefits of step-growth processes has led us toward revisiting the thiol-ene concept for dental composite applications.…”