Reaction Kinetics and Reduced Shrinkage Stress of Thiol–Yne–Methacrylate and Thiol–Yne–Acrylate Ternary Systems

Abstract

Thiol-yne-methacrylate and thiol-yne-acrylate ternary systems were investigated for polymerization kinetics and material properties and compared to the analogous pure thiol-yne and (meth)acrylate systems. Both thiol-yne-methacrylate and thiol-yne-acrylate systems were demonstrated to reduce polymerization induced shrinkage stress while simultaneously achieving high glass transition temperatures (Tg) and modulius. Formulations with 70 wt% methacrylate increased the Tg from 51 ± 2 to 75 ± 1 °C and the modulus from 1800 ± 100 to 3200 ± 400 MPa (44% increase) over the pure thiol-yne system. Additionally, the shrinkage stress was 1.2 ± 0.2 MPa, which is lower than that of the pure methacrylate, binary thiol-yne and thiol-ene-methacrylate control systems which are all > 2 MPa. Interestingly, with increasing methacrylate or acrylate concentration, a decrease and subsequent increase in the shrinkage stress values were observed. A minimum shrinkage stress value (1.0 ± 0.2 MPa) was observed in the 50 wt% methacrylate and 70 wt% acrylate systems. This tunable behavior results from the competitive reaction kinetics of the methacrylate or acrylate homopolymerization versus chain transfer to thiol and the accompanying thiol-yne step-growth polymerization. The crosslinking density of the networks and the amount of volumetric shrinkage that occurs prior to gelation relative to the total volumetric shrinkage were determined as two key factors that control the final shrinkage stress of the ternary systems.

Photo-reactive nanogels as a means to tune properties during polymer network formation

“…Polymer additives have also shown the ability to reduce stress with the replacement of some monomer with variety of prepolymers including oligomer 9 , nanogel 9, 10 or dendrimer 11 . Other techniques include design of new monomers 12 , functionalization of inorganic fillers 13 , or post-gel relaxation based on covalently adaptable networks 14 .…”

Thiol-functionalized nanogels as reactive plasticizers for crosslinked polymer networks

“…As a narrow FWHH is indicative of the presence of a homogenous network such as those generated via a step-growth polymerization reaction (i.e. a thiol-ene reaction), the progressively narrow FWHH observed in Table 1 is a further indication of the thiol-functionalized nanogels being homogenously incorporated within the E9 matrix [Ye et al, 2011]. …”

Assessments of antibacterial and physico-mechanical properties for dental materials with chemically anchored quaternary ammonium moieties: Thiol–ene–methacrylate vs. conventional methacrylate system

“…Glass transition temperature (T g ) was taken as the maximum of loss tangent. The crosslink density ( c ) of cured resins was calculated using DMA data from rubber elasticity theory according to the following equation [19,41,42]:…”

“…Thiol-ene based dental restorative materials are currently attracted much interest as a versatile novel system for overcoming the limitation of conventional methacrylate resins [13][14][15][16][17][18]. The step growth addition mechanism of thiol-ene system result in delayed gelation and consequently significant reduction in shrinkage stress as compared with conventional methacrylate analogous [13,[16][17][18][19]. Lower shrinkage stress and enhanced fracture toughness of the thiol-ene system causes significant reduction in crack development in dental composites [2,20].…”