Ring-opening polymerization of l-lactide catalyzed by a novel molybdenum-based catalytic system
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As a transparent material that can be completely biodegradable, poly(l-lactide) (PL-LA) has recently received considerable attention. In this study, it our first efforts to fabricate l-lactide (L-LA) by a novel molybdenum-based catalytic system consisting of molybdenum pentachloride (MoCl5) as the main catalyst and m-cresol substituted alkyl aluminum Al(OPhCH3)(i-Bu)2 as the co-catalyst. The effects of different types of phosphorus ligands, Al:Mo molar ratios, catalyst contents,catalyst components (separate catalysis of m-cresol aluminum and cocatalysis of Al/Mo system) and polymerization temperature were investigated. The Tg and Tm of the resulting poly(l-lactide) (PL-LA) were characterized by differential scanning calorimetry (DSC), and the molecular weight and molecular weight distribution were determined by gel permeation chromatography (GPC). The GPC results showed that the molecular weight of the PL-LA was higher than that 104 g/mol and the molecular weight distribution was narrow. The structures of PL-LA was detected by 1H NMR spectroscopy (1H NMR) and X-ray diffraction (XRD) validation, which demonstrated that a moalr ratio of Mo/Al/l-lactide = 1:30:1000 showed the higher conversion rate and molecular weight. In comparison to the separate catalysis of m-cresol aluminum, the molecular weight of PL-LA prepared by the cocatalysis of Al/Mo system was slightly improved, and the molecular chains were relatively regular and the crystallinity was higher.
KeywordsMolybdenum-based catalytic system Coordination polymerization l-Lactide Poly(l-lactide) Ring-opening polymerization
The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: The work is supported by the Natural Science Foundation of Shandong Province, China (no. ZR 2016 EMM03).
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