Analysis of Hexaf luoropropylene/Vinylidene Fluoride Copolymers by High Resolution Continuous Wave and Fourier Transform Nuclear Magnetic Resonance Spectrometry E. G. Brame, Jr.,* and F. W. Yeager Elastomer Chemicals Department, Experimental Station, E. 1. du Pont de Nemours & Company, Wilmington, Del. 19898
Continuous wave (CW) and Fourier transform (FT) methods of 19F NMR were used in the quantitative analysis of hexaf luoropropylene/vinylidene fluoride ( HFP/VF2) copolymers. An internal standard procedure was employed with the CW method, that showed the precision to be f8% relative for the HFP determination and f3% relative for the VF2 determination. Only the latter determination used the 'H NMR spectrum for its independent measurement. In the FT method of operation, flat bandwidth response over the 3 5 kHz range required for the composition analysis was found essential. Using only the I9F NMR spectrum for the analysis of these copolymers, the precision was determined to be f 2 to 3 % relative for both components.
Quantitative high resolution NMR analysis by the continuous wave (CW) method has been applied successfully to a wide variety of compounds and complex mixtures for more than 15 years (I). The usual problem is to define the resonance bands of the component(s) of interest and then to calculate composition from their integrated intensities in terms of mole ratio, mole fraction, or weight percent composition. In other cases where it is desired to measure the composition of a single component in a mixture, it is necessary to relate the component resonance to that of another compound, an internal standard, which is of known chemical composition and has been added in known weight to a known weight of unknown. Numerous examples of this technique are discussed by Kasler (I). A major concern in quantitative NMR analysis by the CW method is the error due to selective saturation. Problems relating to optimization of spectrometer conditions to minimize saturation errors have been described by Paulson and Cooke ( 2 ) , and Jungnickel and Forbes ( 3 ) ,and Shoolery ( 4 ) . In this work, the use of a standard has been successfully applied to the compositional analysis of fluoroelastomer polymers. The method was developed specifically for the quantitative analysis of vinylidene fluoride (VFp) and hexafluoropropylene ( H F P ) copolymers; however, it has been found to be generally suitable to the analysis of more complex polymers as well, that is, those polymers containing more than these two components. In a review by D. A. Netzel (!5) on Fourier transform ( F T ) nuclear magnetic resonance spectroscopy, the subject of quantitative analyses was discussed along with the various factors which can affect quantitative results. This discussion is one of the very few on the subject of quantitative analysis as most discussions on pulse Fourier transform NMR do not say very much on the problems relating to quantitative analyses. Farrar and Becker (6) describe the various requirements necessary to perform pulse Fourier transform NMR measurements, even though they do not discuss the measurements directly in terms of the quantitative results obtainable. Freeman and Hill (7) d'iscuss sever-
al different phenomena that may influence relative intensities of lines in pulse Fourier transform NMR. Finally, Farrar (8) describes and illustrates the power distribution of as a function of the the pulsed radiofrequency field, HI, frequency deviation from the reference frequency, VO, a t a number of different pulse widths. Based on this illustration, it is seen that the pulse width must be relatively short (
