Alternating copolymerization of conjugated dienes with methyl acrylate. Part 2.—Isoprene

Abstract

The alternating copolymerization of methyl acrylate (MA) and isoprene (Ip) in the presence of ethylaluminium sesquichloride (Al₂Et₃Cl₃) has been studied. Photoinitiation (λ= 436 nm) was effected by the system Mn₂(CO)₁₀+ CCl₄. Alternation occurs over a wide range of reactant composition.

Copolymerization competes with a rather rapid Diels–Alder addition yielding a mixture of 3-methyl- and 4-methyl-(methyl cyclohex-3-ene-1-carboxylate). Evidence is adduced indicating that the rate of copolymerization is proportional to [MAal][MA_free]°[Ip]°î…ƒ½ where MAal represents the methyl-acrylate–Lewis-acid complex and î…ƒ is the rate of initiation. All the kinetic data are consistent with the cross-propagation mechanism of alternation. The propagation process [graphic omitted] Ip˙+ MA is relatively slow in the absence of Lewis acid, but is markedly accelerated (ca. 88-fold) by Al₂Et₃Cl₃ under the conditions used, with resulting alternation. This enhancement in rate is attributed mainly to weakening of the CC bond in MA which accompanies complexation of the monomer with the Lewis acid.

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