Abstract
The 13C natural abundance undecoupled NMR measurements were carried out on poly(oxy-1,1-dimethylethylene) (PODME) and its model compound, 1,2-dimethoxy-2-methyl-propane (DMMP) in neat liquid as well as in solution over a wide range of temperature. The solvents used were cyclohexane-d12, methylcyclohexane-d14, o-dichlorobenzene, and dimethyl-sulfoxide-d6. Because of the limited solubility of PODME in conventional organic solvents, the measurements for the polymer were undertaken only in o-dichlorobenzene at higher temperatures. The analysis of the undecoupled CH3 signals yielded the vicinal 13C–C–C–H coupling constant, corresponding to an average of contributions from the three rotational isomers defined around the skeletal C–C bond. The values of 3JT and 3JG, and the energy difference between the trans and gauche conformers (Eσ=Eg–Et) were determined from the temperature dependence of the vicinal coupling constant by the least-squares type analysis of Gutowsky. A value of Eσ=0.5 kcal mol−1 was obtained for DMMP irrespective of the solvents used. Nearly the same value was deduced from the analysis of PODME. These results agree well with those obtained from the analysis of the experimental values of the dipole moment of DMMP in nonpolar solvents as reported in paper I. The values of 3JT and 3JG were estimated to be 4.8±0.4 and 2.0±0.2 Hz, respectively.
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Ando, I., Sato, K., Kato, K. et al. Configurational Characteristics of Poly(oxy-1,1-dimethylethylene). II. Conformations around the Skeletal C–C Bond as Determined by the Vicinal 13C-1H Coupling Constant Studies. Polym J 13, 1063–1068 (1981). https://doi.org/10.1295/polymj.13.1063
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DOI: https://doi.org/10.1295/polymj.13.1063
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