Absolute rate coefficients in the alternating copolymerization of methyl acrylate and styrene, including a note on the application of non-stationary conditions to copolymerization

Abstract

A kinetic study has been made of the alternating copolymerization of methyl acrylate (MA) and styrene (St) in the presence of ethylaluminium sesquichloride with photoinitiation (λ= 436 nm) by Mn₂(CO)₁₀+ CCl₄. The reaction was carried out in dilute solution in toluene at 25 °C; variation of [St] over a wide range enabled the kinetic parameters k_bak^–½_tbb and k_abk^–½_taa to be evaluated (k_ba and k_ab being cross-propagation rate coefficients and k_tbb and k_taa termination rate coefficients).

Termination coefficients were determined by the rotating-sector method. The application of this technique to copolymerizations is considered and an equation derived for calculating termination coefficients from sector observations. This procedure is valid so long as the coefficients are independent of the reactant composition.

The cross-propagation coefficients k_ba, k_ab, evaluated from the above data, are found to be large and are compatible with the high degree of alternation observed. It is considered that the simple mechanism of alternation based on dominant cross-propagation is the best representation of the copolymerization.

Reasons for the enhancement of propagation coefficients by the presence of Lewis acids are considered. A major influence on k_ba is attributed to the weakening of the CC double bond in MA brought about by complexation of the latter with Al₂Et₃Cl₃.