Methine carbon resonances, triad chemical

The low field region shows three methine carbon resonances, peaks 1-3. Referring to Terao [2], and concentrating for the moment only at PV(, peaks 1-3 in the solid state cannot simply be assigned to the tacticity induced splitting of the mm, mr and rr triads respectively the relative area intensities of the three peaks in the solid state are not consistent with the triad tacticity observed in solution [2]. Moreover a significant downfield shift of the resonances 1 and 2 occurs compared with the observed chemical shifts for mm and mr triad resonances in solution, which results in much larger mutual chemical shift differences between the methine carbon resonances in the solid. 

The methine proton resonance pattern of poly(vinyl thiophene) is the same as that observed for polystyrene. The lowest field resonance component amounts to 25 percent of the total methine proton resonance and is consistent with poly(vinyl thiophene) being atactic if this lower field component can be assigned to mm triads. Finally, the C-1 carbon resonance spectrum of poly-(vinyl thiophene) (Figure 11) seems to consist of triad resonances, with the lower field area being further subdivided into pentad resonances. This spectrum also suggests that poly(vinyl thiophene) is atactic. If we can conclude on the basis of the results presented here that poly(vinyl thiophene) is indeed atactic, then it seems reasonable to expect the same thing to be true for polystyrene, since the benzene and thiophene rings have very similar steric requirements and similar chemical behavior. 

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