A library of thermoresponsive PEG‐based methacrylate homopolymers: How do the molar mass and number of ethylene glycol groups affect the cloud point?

Abstract

In this study, a novel library of thermoresponsive homopolymers based on poly (ethylene glycol) (EG) (m)ethyl ether methacrylate monomers is presented. Twenty-seven EG based homopolymers were synthesized and three parameters, the molar mass (MM), the number of the ethylene glycol groups in the monomer, and the chemistry of the functional side group were varied to investigate how these affect their thermoresponsive behavior. The targeted MMs of these polymers are varied from 2560, 5000, 8200 to 12,000 g mol −1. Seven PEG-based monomers were investigated: ethylene glycol methyl ether methacrylate (MEGMA), ethylene glycol ethyl ether methacrylate (EEGMA), di(ethylene glycol) methyl ether methacrylate (DEGMA), tri(ethylene glycol) methyl ether methacrylate (TEGMA), tri(ethylene glycol) ethyl ether methacrylate (TEGEMA), penta(ethylene glycol) methyl ether methacrylate (PEGMA), nona(ethylene glycol) methyl ether methacrylate (NEGMA). Homopolymers of 2-(dimethylamino) ethyl methacrylate (DMAEMA) were also synthesized for comparison. The cloud points of these homopolymers were tested in different solvents and it was observed that it decreases as the number of EG group was decreased or the MM increased. Interestingly, the end functional group (methoxy or ethoxy) of the side group has an effect as well and is even more dominant than the number of EG groups.

Liquid–liquid phase separation in aqueous solutions of poly(ethylene glycol) methacrylate homopolymers

“…It should be reminded that the LCST is defined as the minimum point in this curve, even though the terms LCST and CP are often used interchangeably. On the other hand, by increasing the DP, the CP decreases, as it has been previously observed for thermoresponsive homopolymers at low concentrations (normally ~1 w/w%) 32–36 . This trend is more pronounced at low concentrations (up to 15 w/w%) as at 20 w/w%, the CPs are equal within the experimental error (± 1°C).…”

“…Sigma Aldrich Ltd., UK, was the provider of Pluronic® F127 ( M n ≈ 12,600 g mol −1 , ≈ 70% EG), and phosphate buffered saline (PBS) tablets, while phosphate buffer saline (PBS 10× solution) was purchased from Fischer Scientific UK Ltd, Loughborough, UK, and PEG homopolymer ( M n ≈ 6000 g mol −1 ) was purchased from SERVA Electrophoresis GmbH, Germany. The methacrylate homopolymers were in‐house synthesized, via GTP, with their detailed synthesis reported elsewhere 32 . The structural properties of the commercially‐available polymers are provided by the manufacturer, while the structural properties of the in‐house synthesized polymers have been determined via gel permeation chromatography (GPC) and proton nuclear magnetic resonance ( 1 H NMR) spectroscopy, Table 1.…”

Solvent Remodeling in Single-Chain Amphiphilic Heteropolymer Systems

“…Amphiphilic synthetic polymer systems which form compact assemblies in water can adopt extended conformations in solvents of intermediate polarity, within which both hydrophobic and hydrophilic components energetically prefer the enthalpic contributions to solvation over the entropic restriction of compactification, or reverse micelles in solvents which invert typical aqueous behavior, leading hydrophilic components to invert together while hydrophobic moieties preferentially orient to an assembly's surface. This behavior has been experimentally observed for amphiphilic homopolymers with amphiphilic monomers, 13,14 as well as for heteropolymers with both hydrophobic and hydrophilic monomers, most well characterized for 2-component copolymer systems. [15][16][17][18][19] The specific intramolecular interactions dictate how each polymer will adapt, with some systems maintaining monomer contacts in organic media compared to aqueous solvent due to strong intrachain associations which persist in the new environment.…”

Homopolymer and ABC Triblock Copolymer Mixtures for Thermoresponsive Gel Formulations

“…Sigma Aldrich Ltd., Saint Louis, MO, USA, was the provider phosphate buffered saline (PBS) tablets, while phosphate buffer saline (PBS 10 solution) was purchased from Fischer Scientific UK Ltd., Loughborough, UK. The methacrylate polymers, i.e., the four OEGMA300 homopolymers of varying MM values, and the thermogelling triblock terpolymer, OEGMA300 x -b-BuMA y -b-DEGMA z were in-house synthesised, via group transfer polymerisation (GTP), with their detailed synthesis reported elsewhere [57,59]. The structural properties of the in-house synthesised polymers have been determined via gel permeation chromatography (GPC) and proton nuclear magnetic resonance ( 1 H NMR) spectroscopy, but discussion of the synthesis is out of the scope of this study.…”

“…Our group has recently reported a novel combination of methacrylate repeated units, which produces thermoresponsive polymers with a sharp sol-gel transition [56][57][58]. More specifically, the polymers consist of (i) the hydrophilic oligo (ethylene glycol) methyl ether methacrylate with average MM 300 g mol −1 (OEGMA300, A unit), which is also thermoresponsive at approximately 70 • C, depending on the MM [59], (ii) the hydrophobic n-butyl methacrylate (BuMA, B unit), and (iii) the hydrophilic and thermoresponsive (CP approximately 30 • C) [59] di(ethylene glycol) methyl ether methacrylate (DEGMA, C unit). Both ABC triblock copolymers of varying compositions and tetrablock terpolymers of varying architecture were investigated [57,58], with an ABC triblock terpolymer with OEGMA300-BuMA-DEGMA content at 40/35/25 w/w% showing promising thermogelation properties, with the gels being formed at concentrations as low as 2 w/w% [57].…”