CTS-9453369 Christopher N. Bowman/University of Colorado @ Boulder ABSTRACT Highly crosslinked polymers produced from photopolymerizations of multifunctional monomers are suitable for applications as optical lenses, optical fiber coatings, second harmonic generation materials, and dental materials. These types of materials have excellent thermal and dimensional stability, but their application has been limited by certain aspects of the polymerization reaction. The highly crosslinked structure of the polymer networks and the associated low mobilities lead to the formation of a heterogeneous polymer network, autoacceleration kinetics, and reaction diffusion controlled termination. The heterogeneous nature of these polymerizations may cause up to a 500 fold decrease in the mechanical strength, and thus, understanding the relationship between reaction conditions and polymer structure is of the utmost importance in developing improved materials. This work focuses on a fundamental characterization of these polymerizations, as well as the development of materials for applications such as second harmonic generating materials. Polymerization reactions of multimethacrylates, multiacrylates, and other multivinyl compounds will be studied to determine how reaction conditions affect the polymer structural evolution. The structural evolution will be characterized by a variety of techniques including dielectric spectroscopy, transmission electron microscopy, and electron spin resonance spectroscopy. These standard techniques will be used along with two novel techniques that we have recently applied to polymerizing systems: photochromism and second harmonic generation. These techniques are capable of probing the microscopic structure so that quantitative information regarding the heterogeneity and free volume distribution can be obtained. The experimental results from these techniques will be coupled with theoretical predictions from kinetic gelation simulations to obtain a complete pictu re of how reaction conditions such as temperature, initiator concentration, and monomer type affect the heterogeneity and mechanical properties of the crosslinked polymer.
