Comparative quantitative study on the crystallinity of poly(tetrafluoroethylene) including Raman, infra-red and F-19 nuclear magnetic resonance spectroscopy

Wide-angle X-ray scattering (WAXS), F-19 nuclear magnetic resonance (n.m.r.) spectroscopy, differential scanning calorimetry (d.s.c.) and density measurements have been employed to determine the crystallinity of melt-quenched poly(tetrafluoroethylene) samples of different molecular weight. The methods have been checked for consistency before a routinely used infra-red (i.r.) spectroscopic and a recently devised Raman spectroscopic procedure have been correlated with crystallinity as derived by the four conventional methods. The usefulness of the two vibrational spectroscopic methods for determining crystallinity has then been assessed. It was found that WAXS, d.s.c. and density give consistent results in that they clearly show the same trends in the sample crystallinity. In contrast, neither free induction decay nor solid echo pulse sequence n.m.r. correlate with any of these methods, and possible reasons for this behaviour are discussed. Raman as well as i.r. data correlate well with the crystallinity by WAXS, d.s.c. and density. In this respect, both methods are found to be equally useful in estimating crystallinity. (C) 1997 Elsevier Science Ltd.