Copolymerization of l-lactide and ε-caprolactone catalyzed by mono-and dinuclear salen aluminum complexes bearing bulky 6, 6′-dimethylbipheyl-bridge: random and tapered copolymer. Issue 53 (13th May 2016)

• Record Type: Journal Article
• Authors: Kan, Chao; Ma, Haiyan
• Is Part Of: RSC advances. Volume 6:Issue 53(2016)
• Page Start: 47402
• Page End: 47409
• Publication Date: 2016-05-13
• Subjects: Chemistry -- Periodicals; 540.5
• DOI: 10.1039/c6ra07374c
• Languages: English
• ISSNs: 2046-2069

Abstract

Abstract : Mono- and dinuclear salen aluminum complexes bearing a racemic 6, 6′-dimethyl-biphenyl bridge could efficiently catalyze the copolymerization ofl -LA and ε-CL in the melt, producing practically random and tapered copolymers, respectively. Abstract : The mono- and dinuclear salen aluminum complexesL 1–3 AlMe (1, 2, 5 ), L 2 AlO i Pr (3 ), L 2 AlOBn (4 ) andL 1–3 Al2 Me4 (6–8 ) (L = 6, 6′-[(6, 6′-dimethyl-[1, 1′-biphenyl]-2, 2′-diyl)bis(nitrylomethilidyne)]-bis(2-R 1 -4-R 2 -phenol):L 1, R 1 = R 2 = Me;L 2, R 1 = t Bu, R 2 = Me;L 3, R 1 = R 2 = cumyl) with a racemic 6, 6′-dimethylbiphenyl bridge were tested as initiators for the copolymerization ofl -LA and ε-CL. In the presence of alcohol, the mononuclear aluminum complexes catalyzed the controlled copolymerization in the melt at 110 °C, producing practically random copolymers with narrow polydispersity indices ( Đ = 1.03–1.07). Notably, the component of the copolymer produced by complex3 strictly correlated with the feed ratio of the monomers at different stages of the copolymerization. In a 50/50 feed ratio ofl -LA/ε-CL, the reactivity ratios of the two monomers are r LA = 1.17, r CL = 0.80. The average lengths of the lactidyl and caproyl sequences in the resultant copolymer are L LA = 1.91, L CL = 1.93. Even at 180 °C, the copolymerization initiated by complex3 was still well-controlled, producing random copolymers with narrow dispersity indices ( Đ = 1.07–1.09). Compared with the mononuclear counterparts, the dinuclear aluminum methyl complexes enable a few fold boost in activity because of the lower steric hindrance around the aluminum centers, but gave tapered copolymers with broadened Đ values ( Đ = 1.12–1.22).