Induction Curing of Thiol-Acrylate and Thiol-Ene Composite Systems

Induction curing is demonstrated as a novel type of in situ radiation curing that maintains most of the advantages of photocuring while eliminating the restriction of light accessibility. Induction curing is utilized to polymerize opaque composites comprised of thiol acrylate and thiol-ene resins, nanoscale magnetic particles, and carbon nano-tubes. Nanoscale magnetic particles are dispersed in the resin, and upon exposure to the magnetic field, these particles lead to induction heating that rapidly initiates the polymerization. Heat transfer profiles and reaction kinetics of the samples are modeled during the reactions with varying induction heater power, species concentration, species type, and sample thickness, and the model is compared with the experimental results. Thiol-ene polymerizations achieved full conversion between 1.5 min and 1 h, depending on the field intensity and the composition, with the maximum reaction temperature decreasing from 146 to 87 degrees C when the induction heater power was decreased from 8 to 3 kW. The polymerization reactions of the thiol acrylate system were demonstrated to achieve full conversion between 0.6 and 30 min with maximum temperatures from 139 to 86 degrees C. The experimental behavior was characterized and the temperature profile modeled for the thiol-acrylate composite comprised of sub-100 nm nickel particles and induction heater power in the range of 32-20 kW. A 9 degrees C average deviation was observed between the modeling and experimental results for the maximum temperature rise. The model also was 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 method. Finally, induction curing was utilized to cure thiol acrylate systems containing carbon nanotubes where 1 wt % carbon nanotubes resulted in systems where the storage modulus increased from 17.6 +/- 0.2 to 21.6 +/- 0.1 MPa and an electrical conductivity that increased from <10(-7) to 0.33 +/- 0.5 S/m.