Effect of the Substituent Position on the AnionicCopolymerization of Styrene Derivatives: Experimental Results andDensity Functional Theory Calculations

In a combined synthetic, kinetic and theoretical study, the living anionic copolymerization of styrene and its ring-methylated derivatives ortho-, meta-, and para-methylstyrene (MS) was examined by real-time 1H NMR spectroscopy in the nonpolar solvents toluene-d8 and cyclohexane-d12 as well as by density functional theory calculations. Based on the NMR kinetics data, reactivity ratios for each comonomer pair were determined by the Kelen–Tudős method and numerical integration of the copolymerization equation (Contour software). The reaction pathway was modeled and followed by density functional theory (DFT) calculations to validate and predict the experimentally derived reactivity ratios. Unexpectedly, two of the three styrene derivatives showed completely different reactivities in copolymerization, governed by the position of the methyl group. While para-MS is considerably less reactive than styrene, resulting in gradient copolymers (rS = 2.62; rpMS = 0.37), ortho-MS showed the opposite behavior and is mo...