Investigation of Electron Beam Initiated Reactions of Styrenic Block Copolymers

Abstract

Electron beam (E-beam) radiation initiated reactions in styrenic block copolymers (SBCs), including poly (styrene-block-butadiene-block-styrene) (SBS), poly (styrene-block-isoprene-block-styrene) (SIS) and a newly developed poly (styrene-block-isoprene/butadiene-block-styrene) (SIBS) were investigated. The gel content of SBCs after E-beam exposure was calculated and the molecular weight characteristic of soluble portion was analyzed by size exclusion chromatography (SEC). The results showed that gel content increased with increasing of E-beam radiation dose and the low molecular weight material was generated after E-beam exposure. This indicated that both crosslinking and chain scission reactions took place during the E-beam exposure. The crosslinking reaction was the predominating reaction. The structures of gel portion of SBCs were analyzed by solid state nuclear magnetic resonance (NMR). Equilibrium swelling showed that a tighter network was formed at higher radiation dose. Cylindrical morphologies were observed by both small-angle X-ray scattering (SAXS) and atomic force microscopy (AFM). The effect of E-beam on morphologies of ozone etched SBCs was also investigated. It was found that the films of SBCs after E-beam crosslinking were able to maintain a relatively intact morphology after ozonolysis, while SBCs without E-beam cross-linking lost the cylindrical morphology after ozonolysis.