Sequence Selective Polymerization Catalysis: A New Route to ABA Block Copoly(ester-b-carbonate-b-ester)

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• 作者：Shyeni Paul ; Charles Romain ; John Shaw ; Charlotte K. Williams
• 刊名：Macromolecules
• 出版年：2015
• 出版时间：September 8, 2015
• 年：2015
• 卷：48
• 期：17
• 页码：6047-6056
• 全文大小：521K
• ISSN：1520-5835

文摘

The preparation of ABA type block copoly(ester-b-carbonate-b-ester) from a mixture of 蔚-caprolactone, cyclohexene oxide, and carbon dioxide monomers and using a single catalyst is presented. By using a dinuclear zinc catalyst, both the ring-opening polymerization of 蔚-caprolactone and the ring-opening copolymerization of cyclohexene oxide and carbon dioxide are achieved. The catalyst shows high selectivity, activity, and control in the ring-opening copolymerization, yielding poly(cyclohexene carbonate) polyols, i.e., 伪,蠅-dihydroxyl end-capped polycarbonates. It also functions efficiently under immortal conditions, and in particular, the addition of various equivalents of water enables the selective preparation of polyols and control over the polymers鈥?molecular weights and dispersities. The catalyst is also active for the ring-opening polymerization of 蔚-caprolactone but only in the presence of epoxide, generating 伪,蠅-dihydroxyl-terminated polycaprolactones. It is also possible to combine the two polymerization pathways and, by controlling the chemistry of the growing polymer chain-metal end group, to direct a particular polymerization pathway. Thus, in the presence of all three monomers, the selective ring-opening copolymerization occurs to yield poly(cyclohexene carbonate). Upon removal of the carbon dioxide, the polymerization cycle switches to ring-opening polymerization and a triblock copoly(caprolactone-b-cyclohexene carbonate-b-caprolactone) is produced. The ABA type block copolymer is fully characterized, including using various spectroscopic techniques, size exclusion chromatography, and differential scanning calorimetry. The copolymers can be solvent cast to give transparent films. The copolymers show controllable glass transition temperatures from 鈭?4 to 34 掳C, which are dependent on the block compositions.