The 13C NMR spectra of methylstyrenes and methoxystyrenes and their polymers prepared with radical initiators, a Ziegler catalyst, or a cationic catalyst were measured. The spectra of the polymers were assigned by the chemical shifts of the monomers and gated-decoupling method. The absorption of the aromatic C' carbon of each polymer, which varied by the polymerization conditions, was assigned in terms of a pentad sequence assuming that the Bernoullian statistics holds for the polymerization of ring substituted styrenes. The stereoregularities calculated from C' carbon absorptions were compared with those of polystyrenes obtained unter the same polymerization conditions. In the radical polymerization of orthoderivatives, where the substituent locates near the polymer backbone, high syndiotactic polymers (P, = 0,80-0,83) were prepared. The effect of the substituent inpara-derivatives did not appear. On the other hand, random polymers were generally formed by cationic polymerization regardless of the position and the type of the substituent. 0025-1 I 6X/82/0 1 0 125-1 7/$03 .OO Styrene 5,69 (d) 5,18 (d) 6,67 (q) 7,20-7,31 (m) m-Methyl-St 5,68 (d) 5,16 (d) 6,65 (q) 6,99-7,17 (m) 2,28 (s) p-Methyl-St 5,64 (d) 5,13 (d) 6,64 (q) 7,06-7,29 (m) 2,26 (s) o-Methoxy-St 5,72 (d) 5,24 (d) 6,76 (4) 6,85-7,49 (m) 3,77 (s) p-Methoxy-St 5,56 (d) 5,08 (d) 6,63 (q) 6,76-7,32 (m) 3,70 (s)

No abstract

The first highly-resolved 19F n.m.r. spectra in the gas-phase have been observed for 1,2-difluoroethane, and the conformational energy difference between the gauche and trans states has been estimated to be about -0.8 kcal/mol (1 kcal = 4.184 kJ) from the coupling constants observed in the 19F and l H n.m.r. spectra.

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Samples of meso-and roc-2,4-bis-lV-carbazolylpentane were prepared in high purity by the reaction of 2,4-di-O-tosylpentane or 2,4-di-O-mesylpentane with carbazolyl potassium. NMR 1H-1H vicinal coupling constants and their temperature dependence were measured. Statistical weight parameters, and thus conformational energies, estimated therefrom were used to elucidate the conformational characteristics of the polyCZV-vinylcarbazole) (PVK) chain. Experimental values of the characteristic ratios for the unperturbed dimension {r3)0/nP = 15-19 and the dipole moment (µ2) fxm2 = 0.3-0.5 were found to be reasonably reproduced by the calculation for moderately syndiotactic chains. Fractions of the tt conformation were estimated for the meso and racemo diads incorporated in PVK chains: at Pi80 = 0.5, /tt>m = 0-0.05 and /tt>t = 0.43-0.47. In the ground state, the so-called "sandwich structure" (meso-tt) is a rare occurrence.Configurational statistics of the polymer chain may be quite different in the excited state, where formation of the meso-tt form is reported to be very rapid. The conformational energy parameter sets proposed by the other research groups were found to overestimate the meso-tt state to a considerable degree.