Photopolymerization kinetics, photorheology and photoplasticity of thiol–ene–allylic sulfide networks

Abstract

BACKGROUND: Thiol–ene networks are of interest due to their facile photopolymerization and their open network structure. In this work, an allylic disulphide divinyl ether monomer is reacted with tetrathiol and divinyl ether monomers, which allows the network structure to permanently change in shape if stressed while under irradiation. We also study the photo‐differential scanning calorimetry (DSC) kinetics and photorheology during cure and the dynamic mechanical properties after cure.RESULTS: The heat of polymerization is similar for the thiol–ene systems and suggests ca 80% conversion of the vinyl ether groups. An increase in the initiator concentration increases the photocure rate as expected. The activation energy for photopolymerization is 7.6 kJ mol−1. DSC and rheometry studies show that the polymerization kinetics is slowed by the addition of the allylic disulfide divinyl possibly due to the formation of less reactive radicals. However, as shown by dynamic mechanical thermal analysis, the network structure is not changed very much by addition of this monomer. If radicals are generated by irradiation of a photoinitiator in the network while a stress is being applied, the polymer will permanently deform depending on the fraction of 2‐methylenepropane‐1,3‐di(thioethyl vinyl ether) in the network, due to a bond interchange reaction.CONCLUSION: The rate of thiol–ene reaction is slowed by the addition of the allylic disulfide divinyl ether. Photoplasticity is observed in the networks containing the allylic disulfide groups. Further work is required to optimize the extent of photoplasticity in these systems. Copyright © 2007 Society of Chemical Industry

Photomechanics of light-activated polymers

“…The second constant, n or the termination exponent, defines how many radical molecules are needed per termination event. n can be estimated experimentally and for the PNR materials, is found to be unity (Cook et al, 2008;Scott et al, 2006). The photo-cleavage process consumes photo initiators in order to produce free radicals.…”

“…Complete details regarding the material synthesis, sample preparation, and photomechanical experiments have been described elsewhere (Scott et al, 2005(Scott et al, , 2006Cook et al, 2008), and so here we only briefly describe the relevant details.…”

Self-healing coatings

“…Alternatively, Canadell et al [96] demonstrated thermally stimulated self-healing recovery of mechanically damaged rubber promoted by disulphide bond formation. UV radiation has been used as an external trigger to invoke photoplasticity in coatings [106,107].…”

Constitutive model for photo-mechanical behaviors of photo-induced shape memory polymers

“…The material was synthesized following Scott et al (Scott et al, 2005;2006;Cook et al, 2008) and was then cut into flat strips (approximately 30 mm (L) × 8 mm (W) × 0.15 mm (T)) to uniaxial tension to a prescribed strain. While held at this strain, the samples were irradiated with light; the nominal stress was measured during irradiation.…”