Reversible addition-fragmentation chain transfer radical copolymerization of β-pinene and methyl acrylate

The feasibility of radical copolymerization of β-pinene and methyl acrylate (MA) was clarified for the first time. The monomer reactivity ratios were evaluated by Fineman-Ross, Kelen-Tudos and non-linear methods, respectively. The obtained values were r_β-pinene ∼ 0 and r_MA ∼ 1.3, indicating that the copolymerization led to polymers rich in methyl acrylate units and randomly alternated by single β-pinene unit. The addition of Lewis acid Et₂AlCl to the AIBN-initiated copolymerization enhanced the incorporation of β-pinene. Furthermore, the possible controlled copolymerization of β-pinene and MA was then attempted via the reversible addition-fragmentation transfer (RAFT) technique. The copolymerization (f_β-pinene = 0.1) using 1-methoxycarbonyl ethyl dithiobenzoate (MEDB) as a RAFT agent gave copolymers with lower molecular weight and narrower molecular weight distribution. However, the presence of MEDB strongly retarded the copolymerization. Thus a new RAFT agent 1-methoxycarbonyl ethyl phenyldithioacetate (MEPD), which gives a less stable macroradical intermediate than MEDB, was synthesized and introduced to the copolymerization. As anticipated, a much smaller retardation was observed. Moreover, the copolymerization displayed a somewhat controlled features within a certain overall conversion (<∼40%).