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Keywords:

  • block copolymer;
  • thin film;
  • crystal;
  • structure

Abstract

The crystal behavior of a semicrystalline polystyrene-block-poly(l-lactide) diblock copolymer in phase-separated thin films with various thicknesses at different crystal temperatures has been investigated using atomic force microscopy and transmission electronic microscopy. Parallel and perpendicular lamellae could be obtained by annealing the thin films for different periods of time as reported previously (Chen et al., Macromolecules 40:6631 (2007)). At different temperatures, crystallization in thin films with parallel lamellar structure in the melt state gives dendrite crystals with orthorhombic structure, and the ordered structure in the melt is destroyed after crystallization. When crystallization occurs in thin films with perpendicular lamellar structure, crystal morphology and structure are greatly affected by the crystallization temperature (Tc). When Tc < Tg,ps, where Tg,ps is the glass transition temperature of a polystyrene block, crystallization is hardly confined within the lamellae. The morphology is preserved but the long period of the perpendicular lamellae is increased after crystallization. When Tc > Tg,ps, rod-like crystals dominate the final morphology, and crystallinity destroys completely the structure in the melt.© 2012 Society of Chemical Industry