Nuclear magnetic resonance in some fluorine derivatives of polyethylene

Nuclear magnetic resonance studies have been made of the proton and fluorine absorptions in powder samples of polyvinyl fluoride, polyvinylidene fluoride, polytrifluoroethylene, and polytetrafluoroethylene. Measurements were made over a temperature range of 77 to 300°K., and in some polymers up to 420°K. Narrowing of the absorption curves indicates the onset of motion in the temperature region 280–320°K. The activation energies for the narrowing amount to 2–4 kcal. and frequency factors for the motion are about 10 6 to 10 7 sec. −1 , values which are much smaller than those reported for other polymers. Second moments of the absorption curves have been calculated for simple models of motionless and rotating molecules, and have been compared with experiment. The onset of motion in polytetrafluoroethylene is related to transitions reported elsewhere in studies of crystallinity, frictional coefficient, specific heat, and density. Nuclear resonance measurements on fibers of this polymer are in keeping with the view that these physical effects are associated with molecular rotations.