Ethylene Copolymerization with Limonene and β-Pinene: New Bio-Based Polyolefins Prepared by Coordination Polymerization
Kousei Kawamura, Kotohiro Nomura
Abstract
Synthesis of new semicrystalline polymers by copolymerization of ethylene with R-(+)-limonene (Lim) and β-pinene (Pin) has been demonstrated by using phenoxide-modified half-titanocene catalysts, Cp’TiCl2(O-2,6-iPr2-4-RC6H2) (Cp’ = cyclopentadienyl; R = H and SiEt3), in the presence of a methylaluminoxane (MAO) cocatalyst. High-molecular-weight poly(ethylene-co-Lim)s (Mn = 4.09–16.4 × 104) were prepared by using the (1,2,4-Me3C5H2)TiCl2(O-2,6-iPr2C6H3)–MAO catalyst system. Synthesis of high-molecular-weight poly(ethylene-co-Pin)s (Mn = 2.10–22.4 × 104) was attained by using Cp*TiCl2(O-2,6-iPr2-4-R-C6H2) (R = H and SiEt3)–MAO catalyst systems. The comonomer (Lim and Pin) incorporation was affected by the cyclopentadienyl fragment (Cp’) employed. The catalytic activity was affected by the Al/Ti molar ratio and polymerization temperature (at 50 °C), which did not affect both comonomer (Lim and Pin) incorporation and the Mn values significantly. On the basis of microstructural analysis by using 13C nuclear magnetic resonance spectra, these comonomers (Lim and Pin) were incorporated as an isolated unit (due to low comonomer contents, up to 3.6 mol %), and the poly(ethylene-co-Lim)s possessed resonances ascribed to the 1,2-Lim insertion unit and subsequent cyclization (favored 2′,1′-insertion); the degree of 1,2-insertion/cyclization (expressed as the S value) was affected by the Cp’ employed.