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Alternating copolymerization of cyclohexene oxide and carbon dioxide catalyzed by noncyclopentadienyl rare-earth metal bis(alkyl) complexes Part A Polymer chemistry

Zhang, Zhichao, Cui, Dongmei, Liu, Xinli
Journal of polymer science 2008 v.46 no.20 pp. 6810-6818
carbon dioxide, catalysts, catalytic activity, composite polymers, cyclohexenes, molecular weight, yttrium
The syntheses of several dialkyl complexes based on rare-earth metal were described. Three β-diimine compounds with varying N-aryl substituents (HL¹=(2-CH₃O(C₆H₄))N==C(CH₃)CH==C(CH₃)NH(2-CH₃O(C₆H₄)), HL² = (2,4,6-(CH₃)₃ (C₆H₂))N==C(CH₃)CH==C(CH₃)NH(2,4,6-(CH₃)₃(C₆H₂)), HL³ = PhN==C(CH₃)CH(CH₃) NHPh) were treated with Ln(CH₂SiMe₃)₃(THF)₂ to give dialkyl complexes L¹Ln (CH₂SiMe₃)₂ (Ln = Y (1a), Lu (1b), Sc (1c)), L²Ln(CH₂SiMe₃)₂(THF) (Ln = Y (2a), Lu (2b)), and L³Lu(CH₂SiMe₃)₂(THF) (3). All these complexes were applied to the copolymerization of cyclohexene oxide (CHO) and carbon dioxide as single-component catalysts. Systematic investigation revealed that the central metal with larger radii and less steric bulkiness were beneficial for the copolymerization of CHO and CO₂. Thus, methoxy-modified β-diiminato yttrium bis(alkyl) complex 1a, L¹Y(CH₂SiMe₃)₂, was identified as the optimal catalyst, which converted CHO and CO₂ to polycarbonate with a TOF of 47.4 h⁻¹ in 1,4-dioxane under a 15 bar of CO₂ atmosphere (Tp=130 °C), representing the highest catalytic activity achieved by rare-earth metal catalyst. The resultant copolymer contained high carbonate linkages (>99%) with molar mass up to 1.9 x 10⁴ as well as narrow molar mass distribution (Mw/Mn = 1.7).