Effect of Restricted Phase Segregation and Resultant Nanostructural Heterogeneity on Glass Transition of Nonuniform Acrylic Random Copolymers

The glass transition behavior of emulsion polymerized butyl acrylate (BA)−methyl methacrylate (MMA) copolymers was related to their microstructural features. Broad transition regions composed of two distinct peaks were observed in both DMA and DSC measurements of copolymers with various comonomer compositions indicating dynamic and microstructural heterogeneity. This was further investigated using 2D WISE experiment. Nanophase segregation within the copolymers was inferred from detailed analysis of their local dynamic behavior. The length scale of segregation was calculated to be 7.4 nm by 13C NMR spin diffusion experiment. A modeling procedure was also developed to extract the distribution of comonomers compositions within the samples from heat flow first-derivative data. Bimodal comonomer composition distributions were extracted in accordance with their glass transition behavior.