On determination of the tacticity of polyvinyl chloride from high resolution NMR spectra

Tincher, W. C.

doi:10.1002/pol.1962.1206217459

Cited by 50 publications

(15 citation statements)

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“…The computed parameter values are listed in Table V Nomenclature syndiotactic placement; also triad syndiotacticity isotactic placement; also triad isotacticity triad heterotacticity diad syndiotacticity diad isotacticity normalized probability reaction rate constant universal gas constant parameters defined by eqs. (14), (15) ratio r1/rZ absolute temperature, O K differential enthalpy change (kinetic) differential enthalpy change (thermodynamic) differential entropy c.hange (kinetic) variance GTeek Symbols P, 9 persistence ratios 7 , 6 chemical shifts, ppm…”

Section: Resultsmentioning

confidence: 99%

Nuclear magnetic resonance and stereoregularity of PVC

Abdel-Alim

1975

J of Applied Polymer Sci

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SynopsisThe decoupled a-proton spectrum of PVC was examined using a 220 MHz NMR spectrometer. All of the ten possible pentads were detected and an assignment is given based on Bernoullian statistics. This assignment is in general agreement with conclusions reached by previous workers except for some modifications in the heterotactic resonances. Triad tacticity data were obtained from the pentads and were used to estimate the differential enthalpy and entropy changes for bulk PVC polymerized in the temperature range 70°C to -50°C. THEORY Chain Sequence StereoregularityWhen a vinyl chloride monomer unit adds on to a growing chain during freeradical polymerization in a tail-to-head fashion, the carbon-carbon bond of this molecule still rotates even after the molecule tail (CH2-) has been attached. The chlorine atom assumes different spatial positions due to this rotation, and its configuration relative to the rest of the chain is undefined until the next monomer unit adds on. When this happens, the configuration of that particular chlorine atom is fixed. Whether there is or there is not any influence of this configuration on the configuration of the next chlorine atom is a matter of the statistical pattern of addition. Basically, there are two possible configurations for the chlorine atom. If it lies to the same side of the zigzag chain as the preceding chlorine, an isotactic placement has occurred. If it lies opposite to the preceding one, a syndiotactic placement has occurred. Subsequent additions may result in the same configuration or a switch can take place. Figure 1 is a schematic representation of the possible configurations that result from the stepwise addition of four monomer units. Sequences made up of two monomer units are called diads, those of three units are called triads, four monomer units are called tetrads, five are called pentads, and so on. As shown in the figure in triads and higher sequences, we can define a third configuration called heterotactic. This may not be called heterotactic placement. There are only two possible placements, i.e., isotactic and syndiotactic and that is strictly correct for diads. For higher sequences, the word configuration should be used rather than placement. At the bottom of the figure, the possible number of each of the three configurations is shown and also the total number of configurations possible for any sequence length. Thus, there are two diads, three triad configurations, six tetrads, and ten pentads. It'should be noted

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Section: Resultsmentioning

confidence: 99%

Nuclear magnetic resonance and stereoregularity of PVC

Abdel-Alim

1975

J of Applied Polymer Sci

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“…The spectrum of polyvinyl chloride solutions is very complex and its form depends markedly on the frequency of the measurement, the solvent, and the temperature and the data of different investigators do not agree completely [197,199,238,269,270,271,380,597,691,744]. Different methods have been used to interpret the spe~tra of polyvinyl chloride.…”

Section: Polymethyl Methacrylatementioning

confidence: 99%

“…Convincing results were obtained in [691] in which the spectra were plotted at 170°C at a frequency of 60 MHz and a theoretical calculation was carried out on an electronic computer. The author considers that the methyne protons (1) of polyvinyl chloride give a quartet, i.e., part A of a spectrum of type AB.…”

Section: Polymethyl Methacrylatementioning

confidence: 99%

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The NMR of Polymers

Slonim¹,

Lyubimov²

1995

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“…27 The neighbour anisotropy term a AB can be estimated as follows 29 (4) where LlxB( = XB 11 -XBJ_) is the magnetic anisotropy of the B atom and () is the angle between the anisotropy axis and the internuclear vector r AB· However we used the following equation 30 of the magnetic anisotropy of the X-Y bond in-404 stead of eq 4 because of the difficulties in directly estimating on the neighbour anisotropy effect in long chain molecules…”

Section: Theoreticalmentioning

confidence: 99%

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

Ando

Nishioka

Watanabe

1972

Polym J

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ABSTRACT:The proton chemical shifts of meso and racemic 2, 4-dichloropentanes (DCP) were calculated by taking into account the diamagnetic shielding, bond anisotropy and polar effects, using preferred comformations of TG and G'T forms for meso DCP, and TT and GG forms for racemic DCP. The TT form was found to be more stable the GG one by 1.97 kcal/mol. It is predicted theoretically that the anti methylene proton would appear at higher field than the syn proton. Also the orders of the excess charges of the 2p electrons and the total charges on the carbon atoms of meso and racemic DCP's coincide with the order of the observed C-13 chemical shifts of those DCP's.The proton chemical shifts of poly(vinyl chloride) (PVC) were calculated assuming the preferred conformations, (TG)n and (G'T)n for isotactic PVC and (TT)n for syndiotactic PVC. The calculated chemical shifts of racemic methylene and isotactic methine protons appear at a higher field than the meso methylene and syndiotactic methine protons, respectively. As for the isotactic PVC the anti proton appears at higher field than the syn proton just as for DCP.KEY WORDS Poly(vinyl chloride) / Dichloropentane / Chemical Shift / Conformation / Extended Hiickel Method / The proton NMR spectrum of poly(vinyl chloride) (PVC) in solution has long been studied for the stereochemical structure of this polymer, sometimes using decoupling and selective deuteration techniques. 1 -16 Recently Heatley, 16 et al., have studied the vicinal coupling constants of PVC, using a 220-MHz NMR spectrometer and have suggested that in thermodynamically good solvents, the isotactic dyads are in approximate equilibrium between the conformations which result in a 31 helix, whereas syndiotactic dyads are probably in a planar zigzag structure. Also, as the model compounds of PVC, the molecular structure of meso and racemic 2, 4-dichloropentanes (DCP) and isotactic, heterotactic and syndiotactic 2, 3, 6-trichloroheptanes have been studied by infra-red and NMR methods 17 -24 and it has been proposed that the TG and G'T forms are preferred for meso DCP, whereas the preferred form for racemic DCP are predominantly TT, and also GG with some probabilities. Flory, et al.,25 have pointed out the existence of less-favoured conformations. However, these may be almost ignored in our discussion described below.As described above, the molecular structures of DCP and PVC have been studied in detail, but the relationship between the chemical shifts and molecular structures of these compounds have been scarcely studied theoretically. In this paper the calculation of the proton and C-13 chemical shifts of these model compounds in their preferred conformations are described.At first, in the cases of DCP's the extended Hiickel theory 26 was applied to calculate the total electron energies, the total net charges and the excess charges of 2p electrons. Then the proton chemical shifts of these compounds were calculated by taking into account the contributions from diamagnetic shielding, magnetic anisotropy and po...

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On determination of the tacticity of polyvinyl chloride from high resolution NMR spectra

Cited by 50 publications

References 4 publications

Nuclear magnetic resonance and stereoregularity of PVC

Nuclear magnetic resonance and stereoregularity of PVC

The NMR of Polymers

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

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