Stereoselective polymerization of biosourced terpenes β-myrcene and β-ocimene and their copolymerization with styrene promoted by titanium catalysts

Abstract

The stereoselective polymerization of β-myrcene and β-ocimene and their binary copolymerization with styrene promoted by titanium complexes dichloro{1,4-dithiabutanediyl-2,2′-bis(4,6-di-tert-butyl-phenyl)}titanium (1), dichloro{1,4-dithiabutanediyl-2,2′-bis[4,6-bis(2-phenyl-2-propyl)phenoxy]}titanium (2) and Ti(η5-C5H5)-(η2-MBMP)Cl (3) (MBMP = 2,2'methylenebis(6-tert-butyl-4-methylphenoxo)) activated by methylaluminoxane (MAO) is reported. Complex 1 produces a prevalently trans-1,4-polymyrcene (92%), the more sterically encumbered pre-catalyst 2 gives a major amount of 3,4-units (40%). Conversely the pre-catalyst 3 produces cis-1,4-polymyrcene with good selectivity (92%). The catalyst 1 promotes the copolymerization of β-myrcene with styrene giving the corresponding copolymers in a wide range of composition (χs = 0.14–0.90). In the case of β-ocimene the catalysts 1 and 2 produce a polymer with 1,4-trans structure (70%) at 70 °C while at lower temperature (0 °C) an isotactic poly-1,2-ocimene (>99%) is obtained. The catalyst 3 produces a less stereoregular polymer with prevalently cis-1,4-microstructure (55%). The catalyst 2 also promotes the copolymerization of β-ocimene with styrene in a wide range of composition (χs = 0.23–0.87).