Effects of Crystal Growth Conditions on Morphology of Crystalline Syndiotactic 1,2-Polybutadiene

Abstract

The crystalline syndiotatic 1,2-polybutadiene was synthesized with a catalyst consisting of iron acetylacetonate (Fe(acac)3)-triisobutylaluminum (Al(i-Bu)3)-diethyl phosphite (DEP), and the effects of crystal growth conditions on morphology of thin films of the polymer were investigated by transmission electron microscopy (TEM) and electron diffraction (ED) techniques. The polymer with melting point 179 °C was found to have 89.3% 1,2-content and 86.5% syndiotacticity by 13C NMR measurement. The results of electron microscopic studies indicate that the solution-cast thin films of the syndiotatic 1,2-polybutadiene consist of lath-like lamellae with the c-axis perpendicular to the film plane, while a- and b-axes are in the film plane. The morphology of isothermally crystallized thin films of the polymer is temperature dependent. At lower crystallization temperatures (130 °C), a spherulitic structure consisting of flat-on lamellae is formed. With an increase in the crystallization temperature (e.g., at 140 °C), the spherulites and single faceted crystals coexist. At higher crystallization temperatures (150 °C), single crystals with a hexagonal prismatic shape are produced. When the crystallization temperature is above 155 °C, no crystalline structure is observed because of the thermal cross-linking reaction of the double bonds. The melt-draw films contain highly oriented lamellae with its growing direction perpendicular to the drawing direction. According to the orthorhombic packing of planar zigzag chains, the unit cell parameters calculated from the electron diffraction patterns are a = 1.102 nm, b = 0.664 nm, and c = 0.513 nm.