Surface Segregation in Multicomponent Polymers: Poly(acrylonitrile-co-methyl methacrylate) as a Model System

An extensive series of acrylonitrile-methyl methacrylate (AN-MMA) copolymers was synthesized by batch solution polymerization. The series included both statistical copolymers and “blocky” copolymers (average PAN sequence lengths >100). The bulk properties of the copolymers and binary blends of the homopolymers were evaluated by differential scanning calorimetry (DSC) and transmission Fourier transform infrared spectroscopy. Angle-dependent ESCA of the binary blends showed extensive preferential segregation of PMMA to the air surface regions. The statistical copolymers gave ESCA results showing the surface composition to be essentially equivalent to the bulk composition. The blocky copolymers, however, did show an excess of PMMA at the surface despite short PMMA sequence lengths. This is the first spectroscopic demonstration of preferential surface segregation in a nonblock copolymer exhibiting single-phase morphology and thus may serve as a model system for examining factors responsible for such segregation. The results are discussed in terms of the unusual solid-state structure preferred by PAN and high PAN content copolymers.