13C‐{1H} and 1H NMR spectra of the polymers of four monosubstituted thiiranes

Polymers of four monosubstituted thiiranes (R = CH3, butyl, tert‐butyl, C6H5; X = H, D) were prepared using a variety of anionic and cationic catalysts and investigated by 1H and 13C‐{1H} NMR spectroscopy. Four chemical shifts, corresponding to triad structures, were observed for CH carbons with R = tert‐butyl and C6H5, and for CH2 carbons with R = tert‐butyl; also for both CH2 protons with R = tert‐butyl. Two chemical shifts, corresponding to dyad structures, were observed for side‐chain α‐carbons with R = tert‐butyl and C6H5, and for CH carbons with R = CH3 and butyl. For R = CH3 a good correlation was found between the isotactic dyad content determined from the CH carbon spectrum and the CH2 proton spectrum. The proportion of isotactic dyads (σ) varied only slightly with catalyst for R = butyl (σ = 0,5–0,6), more for R = C6H5 (σ = 0,45–0,7), still more for R = CH3 (σ = 0,5–1,0) and yet more for R = tert‐butyl (σ = 0,4–1,0). In the last case the coupling constants for the main‐chain protons in isotactic polymer were JAB(gem) = 12,5, JBC = 11,5 Hz, indicating a preponderance of distorted trans conformations about the main‐chain CC bonds. For R = CH3 the 13C spectrum provides good evidence of a small proportion of head‐head structures in the polymer, about one unit in six being reversed for Mg(ClO4)2 as catalyst and one in twenty‐five for CdCO3 as catalyst. For R = tert‐butyl there was little sign of such structures. The results are discussed in terms of the mechanism.