In Situ NMR Measurement of Reactivity Ratios for the Copolymerization of 3,4-Dimethoxystyrene and para-Substituted Styrene

Abstract

Poly(3,4-dimethoxystyrene-co-styrene) can be used as a precursor for the synthesis of underwater adhesives. The distribution of the comonomer segments in the copolymer chain is critical to the resulting performance of the adhesives. The present study examined the reactivity ratios for the copolymerization of 3,4-dimethoxystyrene and para-substituted styrene by using the Meyer–Lowry, Mayo–Lewis, and Kelen–Tüdös methods, where in situ 1H NMR was employed in monitoring the consumption profile of monomers. The effects of para-substitute groups, reaction temperature, and solvent on the reactivity ratios were studied. It was found that the para-substitute groups (H, methyl, and t-butyl) had little effect on the reactivity ratios for the copolymerization of 3,4-dimethoxystyrene and para-substituted styrene at 70 °C in toluene-d8. A lower reactivity ratio for styrene was found in the copolymerization of styrene and 3,4-dimethoxystyrene in toluene-d8 at a lower temperature of 60 °C than that at 70 and 80 °C. Although 3,4-dimethoxystyrene showed higher reactivity ratios than styrene under all the tested conditions, a nearly random copolymerization behavior was observed for the copolymerization of styrene and 3,4-dimethoxystyrene at 70 °C in the polar solvent DMSO-d6. Based on the present study, it is recommended to carry out experiments covering a large range of monomer mole fraction in feed when measuring reactivity ratios regardless of the analytical methods.