Relation Between Reactivities of Vinyl Monomers and Their NMR Spectra

The ¹sup3;C-NMR chemical shifts of β-carbon (δCβ ) in the vinyl group of various monomers, which depend on the π-electron density on the carbon, were correlated with their reactivity parameters in polymerization reactions. The relations were studied between the δCβ and the e-value of the monomer and direct evidences were obtained for the validity of Q-e scheme. The meaning of Q-value was discussed in some detail from the careful examination of the correlations between the Q-values of homologous monomers and their ¹sup3;C- or ¹H-NMR chemical shifts and coupling constants for the vinyl groups. The method to estimate the monomer reactivity ratios for the copolymerizations of homologous monomers are proposed. The relative reactivities of monomers which were represented by the log(1 / r 1 ) were correlated with the δCβ values in cationic copolymerizations of styrene derivatives the β-carbon resonates at the higher field, the higher the reactivity is. The reverse was the case in anionic polymerizations. The correlations for the cationic polymerization of alkyl vinyl ethers and the coordinated anionic polymerizations of α-olefines were rather complex and the mechanisms of polymerizations were discussed from the results. The ¹H-NMR chemical shifts of vinyl groups of monomers could also be correlated with the reactivities of monomers, particularly among the homologous monomers. These results revealed that the NMR chemical shift of monomer can be used as a measure of reactivity of monomer and is an important tool for the examination of mechanism of polymerization.