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Issue 5, 2016
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Three is company: dual intramolecular hydrogen-bond enabled carboxylic acid active in ring-opening polymerization

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Abstract

Hydrogen-bond organocatalysis using (thio)urea and base has achieved massive success. Intramolecular H-bond (IMHB) assisted Brønsted acid (BA) catalysis, especially in polymerizations, was not explored. Here we suggested an IMHB–BA model in ring-opening polymerization (ROP) with γ-resorcylic acid (RA) as a representative catalyst, promoting ROPs of δ-valerolactone (VL) and ε-caprolactone (CL). The exceptional carboxylic acid RA showed efficient activation and precise control with high conversions (93–98%), predicted molecular weights from 3090 to 13 000 g mol−1, narrow dispersities (Đ 1.02–1.08), and nearly Poisson distributions (Đ ≤ 1.03) at higher molecular weights. A dual IMHB in RA was estimated using computational calculations, which predicted short H-bond lengths and near 180° bond angles, denoting strong H-bonding. A cationic monomer activation mechanism was proposed and supported by NMR titrations. The controlled/living nature of the ROPs was confirmed by kinetics and chain extension experiments. 1H NMR, SEC, and MALDI-ToF MS analyses strongly indicated that the obtained PVL and PCL were exactly the designated ones. Synthesis of well-defined PVL-b-PCL and clickable end-functionalized PVLs again verified that the catalytic ROPs proceeded in a controlled/living manner, and suggested that IMHB–BA catalysis was a generally applicable method.

Graphical abstract: Three is company: dual intramolecular hydrogen-bond enabled carboxylic acid active in ring-opening polymerization

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Publication details

The article was received on 09 Oct 2015, accepted on 08 Dec 2015 and first published on 10 Dec 2015


Article type: Paper
DOI: 10.1039/C5PY01635E
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Polym. Chem., 2016,7, 1111-1120

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    Three is company: dual intramolecular hydrogen-bond enabled carboxylic acid active in ring-opening polymerization

    J. Xu, J. Liu, Z. Li, X. Li, C. Chen, C. Zhao, S. Xu, X. Pan, J. Liu and K. Guo, Polym. Chem., 2016, 7, 1111
    DOI: 10.1039/C5PY01635E

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