Birefringence Effects in Acrylonitrile Polymers. II. The Nature of the 140°C Transition
- 1 October 1965
- journal article
- research article
- Published by AIP Publishing in Journal of Applied Physics
- Vol. 36 (10), 3063-3071
- https://doi.org/10.1063/1.1702928
Abstract
Birefringence measurements on solvent‐cast films of polyacrylonitrile homopolymer under dead load are reported as a function of temperature and as a function of time at constant temperature. It is shown that a large positive birefringence effect is associated with the 240°C aromaticization reaction in PAN. The high negative birefringence state produced by temperature cycling and first reported in Part I of the present series is found to require a small dead load on the sample during cooling for its formation, and is observed to form under conditions of almost constant length. From the interaction between the large negative effect and the positive effects of the nitrile conjugation reaction, it is deduced that the magnitude of the large negative effect is directly proportional to the concentration of nitrile groups present. It is proposed that the 140°C transition in PAN is a result of the association‐dissociation equilibrium between nitrile dipoles on adjacent chains. The temperature dependence of the equilibrium constant for this association is calculated from the birefringence ``cooling curve,'' giving an enthalpy change of 48 kcal/mole, which suggests that association of dipole multiples is involved. Creep, dynamic mechanical, and dielectric loss data from the literature are correlated on the basis of this proposal concerning the nature of the transition.Keywords
This publication has 27 references indexed in Scilit:
- Solid state structure and glass transitions in polyacrylonitrile: The hetero‐bonded solid stateJournal of Polymer Science Part B: Polymer Letters, 1965
- Birefringence Effects in Acrylonitrile Polymers. I. Effects at Different TemperaturesJournal of Applied Physics, 1964
- Coloration in acrylonitrile polymersJournal of Polymer Science Part A: General Papers, 1964
- Thermal coloration and insolubilization in polyacrylonitrileJournal of Polymer Science, 1962
- The Heat Treatment of Orlon Acrylic Fiber to Render it FireproofTextile Research Journal, 1960
- The thermal degradation of polyacrylonitrileJournal of Polymer Science, 1959
- Pyrolysis of polyacrylonitrileJournal of Polymer Science, 1956
- "Orlon" Acrylic Fiber: Chemistry and PropertiesTextile Research Journal, 1950
- Dilatometric Studies of High Polymers. I. Second-Order Transition TemperatureJournal of Applied Physics, 1949
- Electrical Properties of Solids. XIV. Copolymers of Acrylonitrile and Ethyl Acrylate1Journal of the American Chemical Society, 1943