Ternary Thiol−Ene/Acrylate Photopolymers:  Effect of Acrylate Structure on Mechanical Properties

Abstract

Model ternary thiol−ene/acrylate photopolymerization involving acrylate homopolymerization and copolymerization of thiol−ene and thiol−acrylate monomers were monitored by real-time FTIR. In all ternary mixtures, including those prepared with different acrylate concentrations, acrylate conversion was 100%. However, thiol−ene conversions were found to be controlled by their initial concentrations. The influence of acrylate monomer chemical structure on the thermophysical properties of ternary thiol−ene/acrylate systems was studied with DMA, DSC, and the absorbance of a nondestructive impact energy. The addition of acrylate to the thiol−ene system increased the rubbery modulus while the tan δmax shifted to higher temperatures. Densely cross-linked, heterogeneous matrix formation was observed with the broadening of tan δ peaks at high acrylate concentrations. The high impact absorption of these ternary thermoset photopolymers was correlated with the dynamic mechanical damping ability of the networks. Acrylates with higher functionality and low molecular weight per double bond are more effective at increasing the glass transition temperature of the thiol−ene polymer network. Fracture behavior of ternary thiol−ene/acrylate networks under impact shows a dependence on the chemical structure of the acrylate, component concentrations, and low-temperature relaxation processes. The ternary matrix formed with a bisphenol A based difunctional acrylate monomer exhibited improved impact energy absorption at room temperature. Finally, tensile properties of polymer networks formed with thiol−ene/acrylate and thiol−acrylate mixtures are given for comparison purposes.

The preparation and physical properties of polysulfide-based elastomers through one-pot thiol-ene click reaction

“…The results reveal that incorporation of the bisphenol-A structure imparted improved elongation and tensile strength for elastomers, for bisphenol-A unit acts as physical cross-linking point. This effect also has been found in high-energy-absorbing thio-ene and thiol-eneacrylate mixture [11]. On the other hand, with the same molecular weight of PSF oligomers, the ultimate elongation increases significantly from Elastomer-LP2, Elastomoer-LP32 to Elastomer-LP55 (Figure 5b) as well as from Elastomer-LP23 to Elastomer-LP980, but the tensile strength does not have obvious change due to the same dosage of bisphenol-A diacrylate employed.…”

“…This reaction, whether proceeding by a free-radical reaction or Michael addition, carries many of the attributes of click reactions as follows: (a) high yields with minimal byproducts, (b) insensitive to ambient oxygen or water, (c) region or stereospecificity, (d) proceeds under mild, solventless reaction conditions. Up to now, thiol-ene chemistry has been effectively applied in a wide range of disciplines, ranging from surface modification [5][6], polymer functionalization [7][8][9], photolithography and microdevice fabrication [10], high-energy absorbing materials [11][12], applications in biomaterias [13], organic functionalization [14][15], and so on. Usually, there are four low-molecular-weight thiols typically encountered in literatures, including thiophenols [16][17], thiol propionates [5,7,[10][11][12], alkyl thiols [7][8] and thiol glycolates [7,14].…”

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

“…20,21 The glass transition temperature (T g ) and the heterogeneity of thiol-ene-acrylate networks were able to be controlled by varying the amount and chemical structure of the acrylate monomers. 22 The use of addition-fragmentation reactions has also been combined with thiol-ene-methacrylate ternary systems to achieve reduced shrinkage stress. 23 …”

Properties of methacrylate–thiol–ene formulations as dental restorative materials

“…Thus, in all previous (meth)acrylate-thiol-ene studies, 1:1 thiol-ene stoichiometries were exclusively investigated [22,32,38-41]. However, in the cases where both (meth)acrylate and ene functional group conversions were resolved in FTIR, lower ene conversions were reported for many of these systems [22,34].…”