title: Time-resolved X-ray diffraction study on poly[(R)-3-hydroxybutyrate] films during two-step-drawing: generation mechanism of planar zigzag structure.
abstract: Uniaxially oriented films with high tensile strength were processed from ultrahigh-molecular-weight poly[(R)-3-hydroxybutyrate] (P(3HB)) by a method combining hot-drawing near the melting point of the polymer and two-step-drawing at room temperature. In a two-step-drawn and subsequently annealed film, P(3HB) molecular chains fall into two states: 2/1 helix (alpha-form) and planar zigzag (beta-form) conformations. The mechanism for generating the beta-form during two-step-drawing was investigated by time-resolved synchrotron wide- and small-angle X-ray scattering measurements (WAXD and SAXS), together with the measurement of stress-strain curves. It was found that the improvement of mechanical properties is due to not only the orientation of molecular chains but also the generation of the beta-form during the drawing. The crystal and molecular structures of the alpha-form remained unchanged until the yield point of the stress-strain curve. At the yield point, the long period obtained from SAXS doubled and a new reflection indicative of the beta-form was observed on the equatorial line in WAXD. The intensity of the reflection from the beta-form increased with an increase in the two-step-drawing ratio at room temperature. The SAXS pattern changed from a two-point reflection along the meridian to a cross pattern with streaking on the equatorial line, demonstrating the close alignment of shish-kebab structures. The reflection intensity, crystal orientation and crystal size of the alpha-form decreased during two-step-drawing. Based on these results, the beta-form is mainly introduced from the orientation of free molecular chains in the amorphous regions between alpha-form lamellar crystals, but the structural transformation of molecular chains also occurs from the alpha-form to the beta-form at the deformed lamellar crystals.
authors.affiliation: Polymer Chemistry Laboratory, RIKEN Institute, 2-1 Hirosawa, Wako-shi, Saitama 351-0198, Japan. tiwata@riken.jp
authors.forename: Tadahisa
authors.initials: T
authors.lastname: Iwata
authors.forename: Masahiro
authors.initials: M
authors.lastname: Fujita
authors.forename: Yoshihiro
authors.initials: Y
authors.lastname: Aoyagi
authors.forename: Yoshiharu
authors.initials: Y
authors.lastname: Doi
authors.forename: Tetsuro
authors.initials: T
authors.lastname: Fujisawa
mesh_terms: D006885:Hydroxybutyrates / Q000032:analysis* / Q000737:chemistry*; D015394:Molecular Structure; D013997:Time Factors; D014961:X-Ray Diffraction / Q000379:methods
chemical_list: D006885:Hydroxybutyrates