Reaction kinetics and mechanics in photo-polymerised networks

Objectives: The aim of this paper is to address the relationship, existing in photo-cure composites, between the polymer-network forming reactions, along with their kinetics, and the resultant stress-transmitting micro-mechanical behavior. Methods: Photon numbers and energies were calculated and compared for a simple model monomer-composite system. Expressions for light irradiance at depth within materials were computed and the consequences of steady-state assumptions in kinetic models of conversion and shrinkage-strain rate were considered. Results: The resultant stress-transmitting properties are a complex function of photon-transport, absorption by photo-initiators, possibly non-steady-state free-radical cross-linking, collapse of free-volume and development of an elastic-network displaying non-homogenous structure, viscoelasticity and aging effects. Significance: Researchers need to be aware of the complexity of these systems, so as to adequately control experimental variables and to develop more sophisticated models and hypotheses for experimental validation.