CAREER: Characterization of Hybrid Resin Systems Based on Epoxy and Acrylate Functionalities

University Of Iowa, Iowa City IA

Investigators

Abstract

Photopolymerization has experienced tremendous growth within the film, coating and ink industries and is leading to new applications in the biomedical, communications, automotive, and aerospace fields as well. The advantages of using light to initiate polymerization rather than heat include significant savings in energy costs and processing space and time, solvent-free systems, and increased control over the production of initiating species. Of the possible propagation mechanisms, those that are driven by free radical active centers are the most prevalent; however, these polymerizations are plagued by oxygen inhibition. This has increased interest in using cationic photpolymerization schemes, although these suffer from inhibition by moisture and slower cure rates. In order to address the limitations of these polymerization mechanisms, hybrid resin systems have been designed within the past few years to cure using a combination of cationic and free-radical mechanisms under ultraviolet light. These systems exhibit lower sensitivity to oxygen and moisture and offer advantages such as increased cure speed and improved film-forming properties. To date, most studies have focused on the development of these systems; thus, there is a definite need for in-depth studies in order to create a fundamental base of knowledge that allows the impact and utility of these systems to be optimized. This research will investigate hybrid resin systems based on formulations that contain both an epoxide moiety, which undergoes cationic ring-opening photopolymerization, and an acrylate moiety, which undergoes free radical photopolymerization. The goal of this research is to characterize the fundamental kinetics of these hybrid resin systems and to correlate the chemical distribution of the species with the resulting physical properties. This goal will be accomplished by: 1. Investigating the photopolymerization kinetics of the hybrid resin systems. 2. Determining the microscopic composition of the hybrid polymers. 3. Evaluating the mechanical properties of the hybrid polymers. The conversion and rate data for these hybrid systems will be obtained using in-situ Raman experiments and corroborated with photo-differential scanning calorimetry experiments. Raman spectroscopy provides a highly sensitive means of following both cationic and free- radical reactions in real time by monitoring the depletion of the epoxide rings and the acrylate double bonds as they are consumed during the polymerization. The physical nature and properties of the resulting polymers will be investigated with Raman microscopy and dynamic mechanical analysis. Results from this research will address important issues on the interactions between the two polymerization systems and will provide guidance that will aid in the design of these reaction systems for established radiation cure industries, as well as provide opportunities for growth in new areas. This research program will also have a direct impact on the educational experience of students at various levels, including those in junior and senior high school. The Engineering Awareness for Students and Teachers program will be developed to introduce secondary students and teachers from an urban school district to engineering concepts and college preparation strategies through a summer program and classroom activities. Economically disadvantaged students and female and minority students will be recruited in order to increase the opportunities of these underrepresented groups in engineering. This two-pronged approach seeks to increase the impact of the program beyond the students who attend the summer program by supporting their teachers, who will return to their classrooms with materials to introduce all their students to the excitement and challenges of engineering.