Advancing the boundary of insolubility of non-linear PEG-analogues in alcohols: UCST transitions in ethanol–water mixtures?

Soft Matter Pub Date: 2012-12-14 DOI: 10.1039/C2SM27427B

Abstract

Two series of random copolymers of oligo(ethylene glycol) phenyl ether acrylate (OEGPhA) with either oligo(ethylene glycol) methyl ether acrylate (OEGMeA) or oligo(ethylene glycol) methyl ether methacrylate (OEGMeMA) with varying molar fractions of OEGPhA comonomer, comparable molecular weights (～14 kg mol?1) and low molecular weight distributions (1.19–1.36) were prepared by the RAFT process. In aqueous solution copolymers exhibited a lower critical solution temperature (LCST) which decreased linearly with an increasing content of phenyl ethers. In a similar trend of decreasing solubility, the upper critical solution temperature (UCST) of the OEGMeA/OEGPhA series in 2-propanol increased linearly from 11.8 °C to 73.6 °C for (co)polymers containing from 0 to 71 mol% of OEGPhA units. Variable temperature NMR measurements in 2-propanol-d8 performed on a diblock copolymer containing a p(OEGMeA-co-OEGPhA) block and a soluble p(dimethyl acrylamide) block revealed the phenyl ethers to remain solvated to a large extent at temperatures 30 °C below the cloud point of the p(OEGMeA-co-OEGPhA) block. The effect of the phenyl groups decreasing solubility in alcohols was attributed to a promotion of favourable polymer–polymer interactions and a decreased contribution to mixing entropy due to rigidity. For high OEGPhA content a phase diagram in ethanol–water mixtures showed cononsolvency in the LCST regime (high water content) followed by a miscibility gap. The UCST regime, showing a solubility maximum at approx. 80 vol% ethanol extended to ethanol concentrations as low as 55 vol%. UCST transitions in intermediate ethanol–water mixtures, unknown for OEGMe(M)A homopolymers, are believed to increase the applicability of non-linear PEG analogues.

Graphical abstract: Advancing the boundary of insolubility of non-linear PEG-analogues in alcohols: UCST transitions in ethanol–water mixtures
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