Phase Separated Structure and Its Orientation Behavior of Polystyrene-b-Partially Quaternized Poly(2-Vinylpyridine) Thin Films Investigated by Grazing Incidence Small Angle X-ray Scattering

Polystyrene-b-poly(2-vinylpyridine) (PS-b-P2VP) diblock copolymer used in this study was synthesized by living anionic polymerization. The vinylpyridine units in PS-b-P2VP were partially quaternized by 1-bromobutane and the degree of quaternization was controlled in reaction time. The thin filmsof the quaternized diblock copolymer (PS-b-qP2VP) were prepared by spin-coating onto silicon wafers. Subsequently, the films were thermally annealed in a vacuum for given time. The influence of quaternization degrees on the formation and orientation behavior of the phase separated structure (hexagonally packed cylinders) was investigated by grazing incidence small angle X-ray scattering. For as-cast film, the structure in the thin film was disordered and the highly ordered and oriented phase separated structure appeared after thermal annealing. Annealing time to reach the stable structure depended on degree of quarternization and the thin film with high quaternization required a longer annealing time for rearrangement, which might be caused by the qP2VP anchoring on silicon wafers with specific interaction. The ordered cylindrical micro-domains (qP2VP) in the PS-b-qP2VP thin films was found to align parallel to the substrate, respectively. In case of high quaternization, not only parallel cylinders but also other morphology was mixed, or completely different morphology e.g. hxagonally perforated lamellar structure and spherical morphology might form.