Complete Spectral Assignment of Acrylonitrile/Vinylidene Chloride Copolymers by One and Two Dimensional NMR Spectroscopy

Abstract

KEY WORDS Assignment IAcrylonitrileiVinylidene Chloride Copolymers I 20 NMR Spectroscopy I Spectral Over the last decade both one and two dimensional NMR spectroscopy have become an important technique for investigations of the structure of polymers 1 -3 and copolymers. 4 -6 Acrylonitrilefvinylidene chloride (A/V) copolymers has been extensively studied as it is an industrially important polymer. It has potential industrial application because of its excellent fiber formability together with high non-flammability. Many workers have reported the microstructure 7 -10 and reactivity ratios 7 -15 of A/V copolymers. Ito et al. 7 were the first to evaluate the sequence distribution of A/V copolymers by NMR spectroscopy. Bailey et a/. 8 assigned the methylene and the quaternary carbon resonance signals to dyad, triad and pentad sequences. They were not able to assign the methine and the nitrile carbon resonance signals. These signals were assigned to pentad sequences by Konig et a/. 9 and Yamazaki et a/. 10 However, the broad and overlapping 1 H NMR spectra of A/V copolymers has not been assigned by any of these workers.In this paper we report the complete and unambiguous signal assignment of broad and overlapping 1 H NMR spectra of A/V copolymers. The methine and the methylene proton signals were assigned to triad, pentad, heptad and tetrad compositional sequences, respectively, with the help of 2D NMR techniques, like DQFCOSY, TOCSY, and inverse-HETCOR. The various configurational arrangement within the tetrad or pentad sequences were also assigned. EXPERIMENTAL A/V were distilled under reduced pressure and was stored below soc. The A/V chloride copolymers of different monomer composition were prepared by photo polymerization using uranyl nitrate as photo sensitizer in a sealed tube. The percent conversion was kept below 10% by precipitating the copolymers in methanol. The copolymers were purified by N,N-dimethylformamide (DMF)/methanol system. The copolymer composition was calculated from the percent nitrogen of the copolymers and quantitative 13 C NMR spectroscopy.NMR experiments were performed in dimethyl sulfoxide (DMSO)-d 6 on a Bruker 300 MHz spectrometer at frequencies of 300.13 MHz and 75.5 MHz for 1 H and 13 C{ 1 H} NMR spectra, respectively. The 13 C{ 1 H} NMR t To whom all correspondence should be addressed. 396experiments were recorded with 32 K data points for 6000 scans with 2 s relaxation delay. The quantitative 13 C{ 1 H} NMR experiments were carried out using the inversegated decoupling pulse program with 12 s as delay time. The 90° pulse for the 1 H and the 13 C nuclei used was 7.6 JlS and 5.5 JlS, respectively. Two dimensional proton detected 1 H-13 C heteronuclear chemical shift correlation spectra were obtained using the standard pulse sequence. A total of 32 scans were accumulated with a relaxation delay of 2s for each of the 512 t 1 experiments. The DQFCOSY spectrum was obtained with 32 scans for each t 1 value. A total of 512 spectra each containing the 1 K data points were accumulated. Tw...