Carbon-13 NMR chemical shift assignments of poly(vinyl chloride) based on the 2D-INADEQUATE spectrum

Abstract

Two-dimensional (2D) heteronuclear lH-13C, homonuclear lH, and spin-lock relay NMR experiments have been used to provide 13C NMR chemical shift assignments of stereosequences in poly(viny1 chloride). However, relative areas of methylene tetrad peaks based on the assignments given by these 2D NMR experiments do not agree with the relative areas predicted by Bernoullian propagation statietica. Since the methods of the 2D experiments are correct, this is a puzzle. In thie study, tetrad and pentad assignments are proposed on the basis of the carbon-carbon connectivities revealed by the 2D-INADEQUATE (twodimensional incredible natural abundance double quantum transfer experiment) spectrum. The tetrad assignments given by 2D-INADEQUATE experiments show that there are two mmr peaks and that one of them overlaps the mrm peak. These assignments differ from the previous assignments and resolve the contradication in relative peak areas. The relative areas of methylene peaks based on the assignments from the 2D-INADEQUATE spectrum agree with those predicted by Bernoullian propagation statistics. Introductionl3C NMR is the most powerful method to analyze the sequence structures in vinyl polymers. Complicated split peaks arising from pentad or hexad sequences are usually observed in the high-resolution NMR spectra. Recently, two-dimensional (2D) NMR experiments have been developed and used as a reliable method of making assignments in high-resolution spectra.In the field of 13C NMR spectral analysis of poly(viny1 chloride) (PVC), 2D heteronuclear lH-l3C, homonuclear 'H, and spin-lock relay NMR experiments have been used to provide 13C NMR chemical shift assignments of stereosequences in PVC.1*2 Crowther et aL2 have demonstrated (from the spin-lock relay experiment) that the mrm and mmr tetrads are reversed from previous assignment in a similar solvent.314However, the authors found that the relative areas of methylene tetrad peaks based on the assignments given by these 2D experiments1P2 do not agree with the relative areas predicted by a Bernoullian propagation model (selection between m and r). The sample used for this

Two-dimensional NMR studies of acrylate copolymers

“…Various stereochemical arrangements such as diads, triads, etc., in homopolymers can be distinguished by 1D techniques such as 1 H, 13 C{ 1 H}, and DEPT NMR spectroscopy. Nakayama et al [43] have used 2D incredible natural abundance double-quantum transfer experiment (INADEQUATE) spectrum to assign the resonance signals in PVC up to tetrad and pentad sequences on the basis of carbon-carbon connectivity and rectified the previous assignments. The tacticity of poly(methacrylonitrile) (PMAN) [33] has been analyzed up to hexad level for proton and up to tetrad level for carbon nuclei by applying double quantum filtered (DQF)-COSY and HETCOR experiments.…”

Poly(vinylpyrrolidone): Configurational assignments by one- and two-dimensional NMR spectroscopy

“…8 -10 The contribution of two-dimensional NMR spectroscopy to the study of homopolymer microstructure has been universally recognized. [11][12][13] The two-dimensional technique that couples single-bond carbon-proton correlation spectroscopy (2-D HSQC-TOCSY) can help in unambiguous stereochemical and compositional assignments of the polymers. 14 -16 In this article we report the microstructure of PVP and the propagation pathway.…”

Comprehensive Sequence Distribution Analysis of Butyl methacrylate-Acrylonitrile Copolymers by Two-dimensional NMR Spectroscopy

“…As already mentioned these assignments were established by the H a and H b coupling in TOCSY experiment. In AA dyad the three cross peaks along carbon axis were assigned to compositional sequences, BAAB (29,30), BAAA (31)(32)(33) and AAAA (34). These cross peaks along the carbon axis further showed configuration sensitivity along the proton axis.…”