Enhancing the stability of UV‐curable thiol/vinyl carbonate resins

Abstract

In this study, the effect of various stabilizer systems on low‐cytotoxic thiol/vinyl carbonate formulations was evaluated with the aim to inhibit premature dark polymerization reactions. The addition of hydroxybenzene‐based radical scavengers such as pyrogallol (PyG), hydroquinone monomethyl ether (MEHQ), or butylated hydroxytoluene (BHT) resulted in a significantly decelerated increase in viscosity compared to formulations without stabilizers during a defined storage period at 50 °C. The usage of bicomponent stabilization systems in appropriate concentrations further reduced the viscosity increase for nonpigmented formulations. The most effective heterosynergistic stabilization system based on PyG and diisoctyl phosphonic acid (9 mM/90 mM) exerts only a minor influence on the polymerization performance, which was shown by photo‐DSC measurements. The herein presented stabilization of vinyl carbonate/thiol resins exhibits a significant contribution to bringing these low‐toxic building blocks into industrial applications. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44934.

Tough, stable spiroacetal thiol‐ene resin for 3D printing

“…PYG neutralizes radicals in proportion to their concentration and therefore is most effective early in photopolymerization. Ultimately, its ability to scavenge radicals is exhausted, and the polymerization proceeds in a manner similar to stabilized thiol‐ene formulations reported in the literature . Although reducing maximum heat flow is beneficial, the only heat‐generating mechanisms are the thiol‐ene radical transfer and the cleavage of photoinitiator molecules, and therefore the reduction of Δ H that also accompanies the presence of PYG and DIPA likely indicates that fewer thiol‐ene bonds are formed and a less cohesive network is created.…”

“…Thiol‐ene resins have widely varying shelf‐life stability, from under a few hours to several months . In addition to dependence on the structure of the ‐ene moiety, resin shelf‐life can be reduced by dark reactions such as thiol to ‐ene Michael addition, impurities or peroxides generating radical species to induce polymerization, and ground‐state charge transfer complexes formed between thiol and ‐ene groups . Some of the most effective stabilization efforts were obtained by Edler et al .…”

“…In characterizing resin photopolymerization, it is often most informative to report key metrics such as maximum heat flow ( h ), exposure time required to reach maximum heat flow ( t max ), and total enthalpy of polymerization (Δ H ) . These parameters directly correlate to several controllable variables that are important to successful DLP printing.…”

Ab Initio Batch Emulsion Thiol–Ene Photopolymerization

“…For ensuring effective temporal control, the starting emulsion must also be chemically stable before exposure to irradiation, which is generally a challenge with thiol-ene formulations. [39][40][41] Di(tert-butyl)-1,4-hydroquinone (DBHQ), a typical radical inhibitor, was thus added to the DAP-EDDT organic phase (0.02 equiv.). This was found to be an efficient means to prevent premature thiol-ene emulsion polymerization, and maintain a minimum chemical stability of 2 h. Without stabilizer, ene conversion was nearly 60 % after emulsification, whether the initiator was present or not.…”

Modeling the Kinetics and Microstructure of a Thermally Initiated Thiol‐Ene Polymerization

“…to prevent the premature polymerization through spontaneous formation of thiyl radicals. [ 36–39 ] Solution polymerizations were carried out at total monomer concentration in between 40 and 50 wt%. 1, 2, or 3 wbm% (weight percent based on total weight of the monomers) of the initiator AIBN were added to the NMR tube when the solution of the monomers reached the reaction temperature of 65 °C.…”