USE OF LIVING RADICAL POLYMERIZATIONS TO STUDY THE STRUCTURAL EVOLUTION AND PROPERTIES OF HIGHLY CROSS-LINKED POLYMER NETWORKS

Crosslinked polymer networks are used in a wide variety of application s. To use these materials effectively, a fundamental understanding of their structural evolution and the relationship between material prope rties and structure is essential. In this article, a novel technique e mploying ''iniferters,'' i.e., living radical polymerizations, to phot opolymerize these networks is utilized to study the property and struc tural evolution of these highly desirable materials. Living radical po lymerizations are used in this work since this technique avoids the pr oblem of carbon radical trapping encountered while using conventional initiators. Dynamic mechanical measurements are performed on highly cr osslinked methacrylate networks to glean information regarding their s tructural heterogeneity. By performing these measurements on homopolym erized samples at various stages of the reaction and on copolymerized samples of multifunctional methacrylates, the mechanical properties ar e characterized as a function of double bond conversion and comonomer composition. From such analyses, with respect to both temperature and frequency, quantitative conclusions regarding the structure of the net works are drawn. This effort is aimed at exploiting the living radical polymerizations initiated by p-xylylene bis(N,N-diethyl dithiocarbama te) (XDT), to study the mechanical property evolution and structural h eterogeneity of crosslinked polymers which is nearly impossible otherw ise. Polymers examined in this study include networks formed by homopo lymerization of diethylene glycol dimethacrylate (DEGDMA) and polyethy lene glycol 600 dimethacrylate (PEG600DMA) as well as copolymers of DE GDMA and PEG600DMA. (C) 1997 John Wiley & Sons, Inc.