Compositional Effects on Network Structure of Highly Cross-Linked Copolymers of PEG-Containing Multiacrylates with Acrylic Acid

Novel ionizable polymer networks were prepared from oligo(ethylene glycol) (OEG) multiacrylates and acrylic acid (AA), employing bulk radical photopolymerization techniques. The properties of these materials exhibit a complex dependence on the network structure and composition. Dynamic mechanical analysis and penetrant sorption experiments demonstrated that the cross-linked structure of the materials depends very strongly on the AA content, even in cases where the network chain population is expected to be composed solely of ethylene glycol oligomers. The results indicate that interchain interactions are diminished as the AA content is increased, due to the increased spatial separation of OEG chains. The compositional dependence of the glass transition temperature is qualitatively described by a treatment consistent with that employed for polymer blends, and deviations from ideal blend behavior point to the importance of system-specific free volume changes during the radical polymerization process. Hence, the glass transition temperature and other network properties are closely coupled to the polymerization kinetics.