| X-ray methods and molecular modeling have been used to investigate the structure of poly (1,2-difluoromethylene-1,2,3,3-tetrafluoro-4,4-dihydrofuran) (PDTE), poly({dollar}alpha, alpha, alphaspprime, alphaspprime{dollar}-tetrafluoro-p-xylylene)(F-PPX) and poly(monocyano-p-xylylene) (CN-PPX).; PDTE, a ring-containing fluoropolymer has been studied by the pressed films, which are more than 60% crystalline and small angle X-ray data show that these contain lamellae oriented with their long axes parallel to the surface. The wide angle X-ray data show that the chains are perpendicular to the film surface, and have an axial repeat of 9.62 A, probably containing two monomers (an axial advance of 4.81 A per monomer). Molecular mechanics modeling indicates that the most likely structure contains syndiotactic chains in which the monomers have the threo-configuration: such chains are ribbon-like, with an axial advance of {dollar}sim{dollar}4.8 A, in good agreement with the observed repeat.; Films of F-PPX prepared by vapor deposition polymerization are highly crystalline, and have uniplanar orientation. This orientation is maintained on drawing {dollar}times{dollar}10 at 350{dollar}spcirc{dollar}C, when the chains become aligned parallel to the direction of draw, leading to a texture of three dimensionally oriented crystals. 35 X-ray reflections are resolved by controlled rotation and tilting of the drawn specimen, and these can be indexed by a triclinic unit cell with dimensions a = 5.36 A, b = 5.92 A, c = 6.57 A (chain axis repeat), {dollar}alpha = 97.0spcirc, beta = 63.1spcirc{dollar} and {dollar}gamma = 73.1spcirc{dollar}, containing one monomer unit.; Films of poly(cyano-p-xylylene) (CN-PPX) synthesized by vapor deposition polymerization are highly crystalline and can be prepared with uni-planar orientation. This orientation is maintained after drawing the film 700% at 350{dollar}spcirc{dollar}C, when the chains become aligned parallel to the direction of draw, leading to a mosaic texture of doubly-oriented crystals. Three dimensional wide angle X-ray data show that the polymer has a monoclinic unit cell with dimensions a = 5.96 A, b = 13.52 A, c = 6.48 A and {dollar}beta = 135.9spcirc{dollar}, containing two monomer units from symmetry related chains. (Abstract shortened by UMI.)... |
