Polymethacrylic Acid Shows Thermoresponsivity in an Organic Solvent

Abstract

The alternating sequenced copolymer poly-(methacrylic acid-alt-hydroxyethyl acrylate), p­(MAA-alt-HEA), was recently found to display a lower critical solution temperature (LCST) behavior in 1,2-dimethoxyethane (DME), whereas the random copolymer of the same average molecular weight and composition did not. As an effort to understand this peculiar behavior, we investigated solutions of both corresponding homopolymers, poly­(methacrylic acid) (pMAA) and poly­(2-hydroxyethyl acrylate) (pHEA), in DME. We found that in the same temperature range, concentration, and degree of polymerization, pHEA is fully soluble, whereas pMAA shows the LCST behavior similar to the alternating copolymer. On the basis of Hansen’s parameters of the homopolymers, it would be predicted that neither should dissolve in DME. Solubility is therefore connected to specific solvent–polymer interactions and more specifically to the formation of a polymer–solvent complex via hydrogen bonds. We designed a method which combines mid-infrared (MIR) and near-infrared (NIR) spectroscopy in solution to study hydrogen bonding as a function of temperature (by MIR) with simultaneous monitoring of LCST (by NIR). In parallel, the global shape of polymer chains and aggregates was characterized by small-angle neutron scattering in deuterated DME. It is found that pMAA chains form aggregates upon increase of temperature through formation of cyclic H-bonded dicarboxylic dimers. As for pHEA, the solvent’s quality of DME slightly decreases with temperature, but aggregation is prevented by entropic repulsion of the flexible side chains. We thus concluded that nonoccurrence of LCST in the random copolymer is due to the presence of pHEA homoblocks that maintain constant solubility over the whole temperature range.

Catalyst-Free Epoxy Vitrimers Based on Transesterification Internally Activated by an α–CF3 Group

“…In contrast, the FTIR spectrum of the TTA product exhibits a band at 1732 cm –1 corresponding to the CO of the ester functions, overlapping with the split carboxylic acid peak. Such splitting of the carboxylic acid FTIR signal (with two potential maxima around 1700 and 1750 cm –1 ) was already observed on pivalic acid …”

Dicarboxylic acid-epoxy vitrimers: influence of the off-stoichiometric acid content on cure reactions and thermo-mechanical properties

“…The second, whose relative intensity increases with dilution (see ESI) is due to interaction with the solvent (here, the epoxy resin plays the role of the solvent). 51 Once the reaction with epoxy starts, the absorption at 1705 cm -1 diminishes, while absorption at 1735 cm -1 increases, due to the C=O stretching signal of the ester, (overlapped with the solvated COOH one). In parallel, the decay of the characteristic epoxy peak (ν ¯ ≈ 914 cm -1 ) was observed.…”

Unusual Radical Copolymerization of Suprabulky Methacrylate with N-Hydroxysuccinmide Acrylate: Facile Syntheses of Alternating-Rich Copolymers of Methacrylic Acid and N-Alkyl Acrylamide

“…The difference was clearly observed in temperature-variable transmittance measurement (Figure c, cooling process from 60 to −10 °C for 2 mg mL –1 solutions): no change in transmittance with Alt MAA–C18Am , whereas a decrease around 0 °C with Stat 50/50 . As recently reported, PMAA was insoluble in DME at higher temperature but was gradually solubilized during the cooling process: it showed an lower critical solution temperature (LCST)-type thermal response in DME. Such a response was not observed in all of the copolymers, and PC18Am was insoluble in DME regardless of temperature.…”