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-
i
Pr2-4-RC6H2) (Cp’ = cyclopentadienyl;
R = H and SiEt3), in the presence of a methylaluminoxane
(MAO) cocatalyst. High-molecular-weight poly(ethylene-co-Lim)s (M
n = 4.09–16.4 ×
104) were prepared by using the (1,2,4-Me3C5H2)TiCl2(O-2,6-
i
Pr2C6H3)–MAO catalyst system.
Synthesis of high-molecular-weight poly(ethylene-co-Pin)s (M
n = 2.10–22.4 ×
104) was attained by using Cp*TiCl2(O-2,6-
i
Pr2-4-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 M
n 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.
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