13C–{1H} Nuclear Magnetic Resonance Spectroscopy of Poly (vinyl chloride) and its Model Compounds

Abstract

KEY WORDS13C-{1H} NMR / Poly(vinyl chloride) / Configuration / Tacticity / Branching / The 13 C-{1H) high-resolution NMR is of great interest in the study of higher order stereochemical placement of vinyl polymers 1 -4 , because carbon is the most essential atom constituting the skeletal bonds of the polymer chain.Recently Schaefer 5 showed the Fourier Transforms of the noise-decoupled, natural abundance 13 C-{1H) NMR of free induction decays of poly(vinyl chloride) (PVC), but the configurational assignments were not shown clearly.We measured 13 C-{ 1 H} NMR spectra of PVC and its dimer model compounds, i.e., mesa-and racemic-2,4-dichloropentanes. PVC was supplied by Prof. Benoit for the IUP AC Study Programm on Molecular Characterization of Commercial Polymers, and PVC-B was a commercial polymer with relatively high syndiotacticity produced by the Chatillon S.p.A. (Italy).13 C-{1H) spectra were observed by external locked field sweep in absorption mode at 25.14 MHz, using a JNM PS-100 spectrometer. Chemical shifts were represented in terms of parts per million using enriched 13 CH3OH as an external reference. The measurements of NMR were made using the neat liquid for the model compounds and the 20-%(w/v) solution of dimethylsulfoxide for PVC. The a-dichlorobenzene was also used as the solvent for PVC but no significant difference was observed.The NMR samples of PVC were first heated at about 150°C for several minutes to form a uniform solution and then settled at 70°C. At this temperature the solution formed a slightly loose gel and a change in color was not observed during a NMR measurement. Details of NMR measurement 246 are described in ref 3.13 C-{1H) spectrum of the mixture of dimer model compounds, wherein the molar ratio of mesa-isomer to racemic-isomer was approximately 1 : 3, is shown in Figure 1. The assignments of peaks are on the basis of their multiplet structures of weakely proton decoupled 13 C spectrum. All carbons of racemic-isomer appeared in a lower field compared to mesa-isomer. 13C -{1H} spectrum of 1 : 3 mixture of meso-and racemic-2,4-dichloropentane observed at 25.14 MHz, at room temperature.

The Chemical Shifts of Poly(vinyl chloride) and Its Model Compounds

“…Thus the total net charges and the excess charges of the 2p electrons of DCP calculated above are shown in Table IV together with the observed C-13 chemical shifts reproduced from our previous paper. 37 The calculated results showing that each meso carbon appears at higher field than a racemic carbon, agree with the observed results. To show clearly these relationships, the chemical shifts plotted against the total net charges and the excess charges of the 2p electrons are shown in Figure 3, where the reference signal is 13 CH3OH.…”

Carbon-13 NMR Analysis of the Tacticity of Polyacrylamide

“…methine resonance of poly(vinyl alcohol), 2 and is the reverse of those of poly(vinyl chloride) 3 and polyacrylonitrile. 4 Chemical shift assignments should, therefore, be made independently for each vinyl polymer system examined.…”

Nuclear magnetic resonance and stereoregularity of PVC

“…CarmanZ4 measured both tetrads from the &carbons and pentads from the acarbons and was able to assign five distinct resonances to the six possible tetrads. He showed that Bernoullian statistics agreed with his assignments which differed €rom those of Inoue et al 23 Pham et al25 estimated values of differential enthalpies and entropies of activation from triads and tetrads measured by 13C-NMR. They showed that Bernoullian statistics apply to PVC made by freeradical bulk polymerization at 0°C.…”