Crystal Structure and Properties of Isotactic 1,2-Poly(E-3-methyl-1,3-pentadiene)

The resolution of the crystal structure and the physical properties of isotactic 1,2-poly(E-3-methyl-1,3-pentadiene) (iPE3MPD) are presented. This new polymer is one of the very few examples of known crystalline isotactic 1,2-polydienes. It does not crystallize by cooling from the melt but crystallizes by aging the amorphous samples at room temperature for several days and successive annealing. The stretching of amorphous or low crystalline compression-molded samples gives oriented fibers of a highly disordered mesomorphic form. Well-oriented fibers of the ordered crystalline form of iPE3MPD have been prepared by stretching amorphous or low crystalline compression-molded samples and successive annealing at 60–70 °C under tension. The crystalline structure of iPE3MPD is characterized by macromolecules in 7/2 helical conformation packed in an orthorhombic unit cell with parameters a = 17.4 Å, b = 16.5 Å, c = 15.3 Å according to the space group P21ab. iPE3MPD has shown interesting mechanical properties of high deformability with elastic behavior associated with the crystallization during deformation of the mesophase that melts upon relaxation.