Fluorine magnetic resonance spectra and tacticities of poly(vinyl trifluoroacetate)

Fluorine magnetic resonance spectra of poly(vinyl trifluoroacetate) samples of different tacticities were investigated, along with those of model compounds. These polymers represent the first case where the line order in respect to stereostructure does not agree with that expected from the spectra of model compounds. More than four peaks were observed for signals from the trifluoromethyl groups of the polymers and the relative peak positions differed from those previously reported. The intensity ratios of the peaks were affected by the solvent employed. Therefore the spectra cannot be interpreted in terms of triad stereosequences. Seemingly longer stereosequences or other influences have to be considered to interpret the spectra.     

NMR spectra of model compounds of poly(vinyl chloride)

The NMR spectra of three stereoisomers of 2,4,6-trichloroheptane as model compounds of poly(vinyl chloride) have been studied. Spectra were observed at 60 and 100 Mc./sec., both at room temperature and at high temperatures. A spin-decoupling experiment was performed. Computational analysis of the spectra was carried out on an IBM 7090 computer. The difference of the chemical shifts of the two meso methylene protons at 60 Mc./sec. was found to be ca. 7 cps. for the isotactic three-unit model while it was ca. 16 cps. for the isotactic two-unit model or heterotactic three-unit model. The spectra of poly(vinyl chloride) were interpreted reasonably on the basis of this result. Observed values of vicinal coupling constants of model compounds were interpreted as the weighted means of those for several conformations, and the stable conformations of the models were determined.     

The fluorine magnetic resonance spectrum of poly(vinyl fluoride)

High resolution fluorine magnetic resonance spectra have been obtained for poly(vinyl fluoride) at elevated temperature. Proton noise-decoupling and time-averaging techniques have given new tacticity and sequence information.     

The proton magnetic resonance spectra of d-aldosterone and its acetylated derivatives

PMR spectra of d-aldosterone, its acetylated derivatives and related compounds were studied using 60 and 100 MHz spectrometers at various temperatures, in CDCI₃, DMSO-d₆, CD₃OD and D₂O. The aldehyde form ( 1 ) was not found. The solutions of d-aldosterone and aldosterone-21 acetate contain a mixture of the cyclic forms with one (11–18) hemi-ketal bridge ( 2 ) and two (11–18, 18–20) hemi-ketal bridges ( 3 ). Preliminary results concerning modifications of the relative concentration of 2 and 3 obtained by varying solvents and temperature are given. Aldosterone-diacetate exists in only one form, most likely form 2 . There is restricted rotation of the group at C-21 in d-aldosterone and in form 3 of aldosterone 21-acetate. One molecule of water is probably bound to d-aldosterone.     

Conformational analysis of poly(ethylene oxide) and model compounds by nuclear magnetic resonance spectroscopy

In order to determine the conformation of poly(ethylene oxide) (PEO), ¹³C satellite spectra of PEO, 1,2-dimethoxyethane (DME), and dioxane were measured at various temperatures in various solvents, and analyzed. Relations between the coupling constants were derived from the linearity between the parameters N = J_AB + J_A′B and L = J_A′B in AA′BB′ spectra of PEO and DME. The vicinal coupling constants for the individual rotational isomers were obtained from the above relations and the temperature dependences of N and L and the enthalpy differences were calculated in each solvent. The gauche rotamer is more stable than the trans isomer by 250–500 cal/mole in all cases examined.     

13C nuclear magnetic resonance spectra of polyacrylates and their model compounds

¹³C nuclear magnetic resonance spectra (¹³C-NMR) of poly(methyl acrylates) and poly(isopropyl acrylates) of various tacticities were measured at 25.1 MHz and analyzed. ¹³C-NMR spectra of model compounds for poly(methyl acrylate), poly(acrylic acid), and poly(sodium acrylate) were also determined. The spectra of the polymers were generally complicated owing to the splittings corresponding to triad, tetrad, or pentad placements, and the assignment for each peak was difficult. Groups of peaks were analyzed by triad or tetrad placements by assuming Bernoullian or first-order Markovian statistics.     

Wide-line proton magnetic resonance spectra of some celluloses

Characteristic wide-line proton magnetic resonance absorption spectra of a number of representative cellulose preparations have been obtained in the dry state and after addition of about 7% water. Line widths, second moments, spin-spin and spin-lattice relaxation times have been determined. The second moment of the absorption curve of dry cellulose was found to correlate well with the crystalline fraction for most specimens. A technique is described for determining the number of water-cellulose protons exchanging relative to the number of cellulose protons not exchanging. The reduction in absorption line width observed when water is added to cellulose is shown to be quantitatively consistent with such a proton exchange phenomenon.     

Fluorine NMR spectra of poly(vinyl trifluoroacetate)

Samples of poly(vinyl trifluoroacetate) with differing stereosequences have been prepared. The NMR signals at 56.4 Mc./sec. corresponding to the three types of triadstereosequences of the trifluoroacetate groups (isotactic, heterotactic, and syndiotactic) can be resolved. The results for specific polymers are discussed.     

High-resolution solid-state NMR studies of poly(vinyl phosphonic acid) proton-conducting polymer: molecular structure and proton dynamics

The structure and the local proton mobility of poly(vinyl phosphonic acid) were studied by solid-state NMR under fast magic-angle spinning. At elevated temperatures, the signature of the hydrogen-bonded P-OH protons is observed in 1H magic-angle spinning (MAS) NMR as a single resonance at 10.5 ppm. Both 1H double-quantum NMR and variable-temperature experiments demonstrate that P-OH protons are mobile and thus able to contribute to proton conductivity. Below room temperature, two different types of hydrogen-bonded P-OH resonances are observed at 10.5 and 15 ppm, and 1H double-quantum NMR demonstrates that these protons are immobile on the NMR time scale. By means of first-principles calculations of a model polymer, we have assigned the additional hydrogen-bonded species at lower temperatures to phosphonic acid anhydride and charged anhydride. Also, in the 31P MAS NMR spectrum, two distinct resonances appear, arising from "normal" phosphonic acid and phosphonic acid anhydride. 31P double-quantum NMR experiments reveal that there is no phase segregation between normal and phosphonic acid anhydride and the condensation reaction occurs randomly throughout the system. The formation of acid anhydride leads to a decrease in proton conductivity through two mechanisms, (1) decrease in the number of charge carriers and (2) blockage of charge transport pathways through immobilization of charge carriers together with a hindered reorientation of the anhydride group. Our results provide strong evidence for these mechanisms by demonstrating that the conductivity is greatly influenced by the presence of phosphonic acid anhydride.     

Study on thermal behavior of thermooxidized poly(vinyl formal)

The thermal behavior of thermooxidized poly(vinyl formal) has been investigated by means of thermogravimetry, derivative thermogravimetry, and differential thermal analysis. As a result, it has been clarified (1) that thermal decomposition is composed of three weight loss processes, (2) that, when investigating the ratic of percentage of weight remaining in each process, the behavior differs for each both before and after the thermooxidizing time of 2–4 h; the second weight loss process caused by formation of crosslinking structure prevails in the initial stage of thermooxidation while the first weight loss process caused by decomposition of various types of thermooxidation products such as unsaturated bonds and crosslinking prevails as the thermooxidation proceeds, and (3) that the volume of carbonaceous residue produced as the thermooxidation advances increases about 4 times. When kinetic parameters have been evaluated by applying the Coasts and Redfern method to each weight loss process, on the other hand, it is concluded (1) that each order of reaction is first and (2) that the value of activation energy in the third process of carbonization and burning reaction is substantially lowered as the process of the thermooxidation advances.     

Photoreversible reactions of poly(vinyl cinnamylideneacetate) and its model compound

Photochemical reactions of poly(vinyl cinnamylideneacetate) and its model compound were studied. The irradiation of these compounds with light of wavelength longer than 300 nm produced dimeric forms of cinnamylideneacetyl groups, which were effectively dissociated into the monomeric forms by the irradiation with 254 nm light.