Thiol-Ene/Yne Photopolymerization

To address challenges related to developing photocurable resin and composite systems combining high modulus and low shrinkage stress, this thesis was focused on understanding and investigating the interrelationships between monomer formulations, curing conditions, and material properties in photopolymerizable thiol-ene/yne formulations. By evaluating various radical photocuring systems including chain-growth, step-growth and mixed chain-step-growth systems, a relationship between glass transition temperature (Tg) and curing conditions was developed. Tg was quantified as a function of the network mobility which is related to the cure temperature (Tcure), the maximum achievable glass transition temperature (Tgmax), and the network heterogeneity (Tg1/2width). Deviations between the theory and experiments were found to be approximately 10%. The ternary thiol-yne-(meth)acrylate systems were evaluated for their potential to achieve simultaneously outstanding Tg and modulus and low shrinkage stress. The crosslinking density and the amount of volumetric shrinkage that occurs prior to gelation relative to the total shrinkage were determined as the two dominant factors that control the final shrinkage stress of the ternary systems which was reduced by more than 40% in the ternary system as compared to either pure monomer formulation. To increase the modulus further, silica nanoparticles functionalized by a 16-functional hyperbranched alkene were incorporated into this ternary resin, which demonstrated 30% reduced shrinkage stress without sacrificing the modulus (3200 ± 200 MPa) or Tg (62 ± 3 °C). Moreover, it was observed that the shrinkage stress of the composite builds up at much later stages of the polymerization. Finally, an induction polymerization method was developed as an alternative to UV curing to address challenges associated with the restriction of light accessibility in highly filled composite systems. This method was able to cure completely samples up to 1 cm thick in as little as 2 minutes. The reaction kinetics of thiol-ene and thiol-acrylate systems were studied and a model of heat transfer profiles combined with reaction kinetics was developed and utilized to predict reaction temperatures and kinetics for systems with varying thermal initiator concentration, initiator half-life, monomer molecular weight and temperature gradients in samples with varying thickness; thereby demonstrating that induction curing represents a designable and tunable polymerization metho