Alternating copolymerization of conjugated dienes with methyl acrylate. Part 1.—Butadiene

Abstract

A study has been made of the alternating copolymerization of methyl acrylate (MA) and butadiene (Bd) in the presence of the Lewis acid ethylaluminium sesquichloride (Al₂Et₃Cl₃), photoinitiated (λ= 436 nm) by the system Mn₂(CO)₁₀+ CCl₄. Alternation occurs over a wide range of reactant composition, and the contents of trans-1,4 and 1,2 butadiene units in the alternating copolymers have been estimated as 90% and 10%, respectively.

Measurements at low conversion show that the rate of copolymerization is proportional to [MAal][MA_free]°[Bd]°î…ƒ^½, where MAal represents the methyl-acrylate–Lewis-acid complex and î…ƒ is the rate of initiation. This reaction is accompanied by the Diels–Alder addition yielding methyl cyclohex-3-ene-l-carboxylate (MCC), proceeding at a rate proportional to [MAal][Bd].

At longer reaction times the overall kinetic features reflect the competition between these two processes. Kinetic data on the copolymerization are shown to be consistent with the simplest mechanism of alternation, namely that based on predominating cross-propagation. Propagation between [graphic omitted] Bd˙ and MA, which is relatively slow in the absence of Lewis acid, is greatly accelerated (ca. 33-fold) by Al₂Et₃Cl₃ under the conditions used, and so gives rise to alternation.

Chain-transfer to CBr₄ has been observed and the appropriate kinetic parameters evaluated.