The Crystal Structure of Polytetrafluoroethylene, Forms I and IV

Polytetrafluoroethylene (PTFE) is unusual among polymers in that it has four crystal phases, designated I–IV, with two of the phases (I, IV) incorporating substantial angular motion (librations) of linear segments within a precisely defined lateral lattice array. Data not included in the authors' earlier publications are presented to interpret two unsolved aspects of the crystal structure: 1) the narrow (11K) range of Form IV (1 atm) and 2) the possibility of another transition in Form I. The existence of Form IV is attributed to an “energy well” from space group P31. The molecular behavior in Form I is attributed to (L–R) molecular defects (changes in chirality) that increase rapidly in number and speed of translation along the axis with increasing temperature.

[1]  K. Perepelkin.  Fluoropolymer Fibres: Physicochemical Nature and Structural Dependence of their Unique Properties, Fabrication, and Use. A Review , 2004 .

[2]  D. B. Holt,et al.  Modeling of helix reversal defects in polytetrafluoroethylene: II. Molecular dynamics simulations , 1999 .

[3]  D. B. Holt,et al.  Modeling of helix reversal defects in polytetrafluoroethylene: I. Force field development and molecular mechanics calculations , 1999 .

[4]  E. S. Clark.  The molecular conformations of polytetrafluoroethylene: forms II and IV , 1999 .

[5]  G. Strobl,et al.  Chain Reorientation in Poly(tetrafluoroethylene) by Mobile Twin-Helix Reversal Defects , 1994 .

[6]  Takashi Yamamoto.  Monte Carlo simulation of the crystal structure of the low‐temperature phase of polytetrafluoroethylene , 1985 .

[7]  Takashi Yamamoto,et al.  X-ray diffraction study of crystal transformation and molecular disorder in poly(tetrafluoroethylene) , 1982 .

[8]  S. Naya,et al.  A Statistical-Mechanical Theory of Structural Phase Transition in Helical Polymer Crystals , 1982 .

[9]  J. J. Weeks,et al.  Crystal structure of the low temperature phase (II) of polytetrafluoroethylene , 1981 .

[10]  B. Farmer,et al.  Energy calculations of the crystal structure of the low temperature phase (II) of polytetrafluoroethylene , 1981 .

[11]  J. J. Weeks,et al.  Diffraction from Nonperiodic Structures: The Molecular Conformation of Polytetrafluoroethylene (Phase II) , 1980 .

[12]  Hiroshi Tanaka,et al.  Studies on the High-Pressure Phases of Polyethylene and Poly(tetrafluoroethylene) by Raman Spectroscopy , 1980 .

[13]  K. Matsushige,et al.  Fine Structure of the III-I Transition and Molecular Motion in Polytetrafluoroethylene , 1977 .

[14]  E. S. Clark.  Molecular motion in polytetrafluoroethylene at cryogenic temperatures , 1967 .

[15]  L. Muus,et al.  Partial disordering and crystal transitions in polytetrafluoroethylene , 1962 .