Effects of prepolymer structure on photopolymer network formation and thermomechanical properties

Photopolymerization is a growing field within the realms of polymer and material science. With diverse applications, ranging from coatings and adhesives to newer technologies such as 3D printing photopolymerization continues to increase its prevalence and influence. This research examines fundamental structure property relationships between large prepolymer structures within a formulation and the resulting impact on thermo-mechanical properties in photocurable resins. Most prepolymer molecules utilize a “one pot” synthesis with little to no control over the placement of photoreactive moieties such as epoxies and (meth) acrylates. We have utilized novel prepolymer molecules synthesized using controlled radical polymerization to allow direct control over the placement of reactive groups. The ability to control the location of reactive groups in prepolymer molecules can also lead to the formation of multiple domains within the resulting photocured thermoset. This separation is achieved by concentrating the reactive groups at specific locations in the prepolymer backbone, e.g. at the end or near the center of the prepolymer molecule. The nonreactive groups may form one domain within the thermoset network while the reactive portion of the prepolymer forms a second phase with reactive diluent molecules. Additionally, various architectures allow greater control over polymer network formation and crosslink density. Through these manipulations of macromolecular architecture, we have been able to manipulate various thermo-mechanical properties. Using various architectured prepolymer, we have been able to generate materials with multiple glass transitions while also increasing the rate of reaction and total conversion as compared to randomly functionalized control formulations.