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Issue 21, 2020
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Indium phosphasalen catalysts showing high isoselectivity and activity in racemic lactide and lactone ring opening polymerizations

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Abstract

Stereoblock polylactide (PLA) shows higher melting temperatures and better mechanical properties than other PLA stereoisomers. More stereoselective and active catalysts are needed to polymerize racemic-lactide (LA) and produce stereoblock PLA. This work describes a series of phosphasalen indium catalysts (1–5) which result in very high isoselectivity, at room temperature, (Pi = 0.91, 25 °C) and high activity, at low catalyst loading (TOF = 100 h−1, 1 : 500 catalyst : LA, [LA] = 1 M, THF, 25 °C). The catalyst structure–activity and structure–stereoselectivity relationships are investigated using various experimental methods and DFT calculations. The most isoselective catalyst features two different phosphasalen substituents, a tert-butyl and phenyl group, it forms an achiral, meso indium complex which operates by a chain end control mechanism. The work highlights the benefits of phosphasalen ligands and identifies new avenues for catalyst investigation by exploitation of asymmetrically substituted phosphorus atoms. The catalysts also show good activity and control for the ring-opening polymerizations of ε-caprolactone, β-butyrolactone, ε-decalactone and δ-hexalactone (γ-methyl-δ-valerolactone), demonstrating future potential for copolyester production.

Graphical abstract: Indium phosphasalen catalysts showing high isoselectivity and activity in racemic lactide and lactone ring opening polymerizations

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Supplementary files

Article information


Submitted
24 Jul 2020
Accepted
25 Aug 2020
First published
18 Sep 2020

This article is Open Access

Catal. Sci. Technol., 2020,10, 7226-7239
Article type
Paper

Indium phosphasalen catalysts showing high isoselectivity and activity in racemic lactide and lactone ring opening polymerizations

N. Yuntawattana, T. M. McGuire, C. B. Durr, A. Buchard and C. K. Williams, Catal. Sci. Technol., 2020, 10, 7226
DOI: 10.1039/D0CY01484B

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