602 WILLIAMS
Macromolecules
Nuclear Magnetic Resonance Studies of Poly (N-vinylcarbazole ) David J. Williams
Research Laboratories, Xerox Corporation, Xerox Square, Rochester, New York 14603. Receiced February 3, I970
ABSTRACT: The high-resolution nuclear magnetic resonance spectrum of poly(N-vinylcarbazole) has been recorded in various solvents for samples prepared by a number of different methods of polymerization. Spectra were also recorded for a series of copolymers of N-vinylcarbazole and ethyl acrylate of different compositions. The spectra indicate the presence of hindered rotation with temperature-dependent populations of conformers. Shielding effects resulting from interactions between neighboring carbazyl groups are discussed. The tacticity of the polymer appears to be fairly insensitive to the method of polymerization.
H
igh-resolution nmr spectroscopy has been used extensively in recent years to obtain information o n the structure of polymers. Much attention has been directed toward the elucidation of the microstructure of polymers and copolymers. The effects of tacticity o n nmr chemical shifts have been studied extensively. 1 Copolymer sequence distribution effects o n nmr chemical shifts have also been the subject of considerable attention.2, The problem of polymer conformation has been considered and has generally taken the form of reconciling the spectrum of the polymer with that of low molecular weight model compounds. The 2,4-disubstituted pentanes have served as model compounds for a number of polymers and have provided an understanding of the solution conformation for polymers such as polystyrene4p5 and poly(vinylpyridine),6 as well as others. The observation of hindered rotation in a polymer has been reported by Bovey and Tiers7 for the rotation of the amide bond in solutions of poly(acry1amide) and poly(methylacry1amide). I n that study the effect of the polymeric environment o n the amide group rotation was examined and no observable effect was found. Poly(N-vinylcarbazole) (PVK) appears t o offer a system for study by nmr where hindered rotation in the polymer results from the steric constraints of the polymeric environment. The nmr spectrum of PVK was PVK +CH-CH,+
first reported by Heller, et a1.8 The chemical shifts of the lines corresponding t o the various protons were subsequently assigned by Yoshimoto, et al.9 They (1) F. A. Bovey, Accounts Chem. Res., 1 , 175 (1968). (2) F. A. Bovey, J . Polym. Sci., 62,197 (1962). (3) T. K. Wu, J . Phys. Chem., 73, 1801 (1969) (see references cited therein). (4) F. A. Bovey, F. P. Hood 111, E. W. Anderson, and L. C. Snyder, J . Chem. Phys., 42,3900 (1965). ( 5 ) F. Heatley and F. A. Bovey, Macromolecules, 1, 301 (1968). (6) G. Weill and G. Herman, J . Polym. Sci., Part A-2, 5, 1293 (1967). (7) F. A. Bovey and G. V. D. Tiers, ibid.,Part A , 1,849 (1963). (8) J. Heller. D. 0. Tiezen, and D. B. Parkinson, ibid., Part A , ~ l125 ; (1963). (9) S . Yoshimoto, Y. Akana, A. Kimura, H. Hirata, S. Kusabayashi, and H . Mikawa, Chem. Commun., 987 (1969).
assigned a peak at 7 8.5 to the methylene protons and two peaks at 6.4 and 7.3 to a methine proton, a peak at 5.0 t o a n aromatic proton, and several peaks at 3 to the remaining aromatic protons. The large upfield shift t o 5 of one of the aromatic protons is attributed to the shielding effects of neighboring carbazyl groups o n a polymer chain with restricted internal rotation. We have examined the nmr spectrum of PVK in order t o elucidate the interpretation of the existing data and provide a more thorough understanding of the nature of the interaction between the carbazyl groups. Samples of PVK prepared by a number of different methods were examined in order to determine if differences in tacticity could be introduced by the various methods of polymerization. The temperature dependence of the nmr spectrum of PVK was also examined. A temperature-dependent nmr spectrum would be observed (a) if conformer populations are temperature dependent even though they may be exchanging rapidly on an nmr time scale or (b) if the exchange rates between conformers are comparable t o their differences in chemical shifts. In the latter case the relative populations of conformers may or may not change with temperature. l o We have also examined the nmr spectrum of various compositions of copolymers of ethyl acrylate and NPVK-EA +CH-CH,
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