Exploring the role of deep eutectic solvents in enhancing the properties of PMMA for potential electrolyte films

In this study, a novel series of solid PMMA containing deep eutectic solvent (DES) (PMMADES) (Mw = ∼28,374 g mol−1) was successfully synthesized via free radical polymerization of methyl methacrylate (MMA) in different types of DES (e.g., choline chloride (ChCl): 1,2-butanediol (1,2-BD)-DESI, ChCl: 1,3-butanediol (1,3-BD)-DESII, and ChCl: 1,4-butanediol (1,4-BD)-DESIII) in order to overcome the brittleness of commercial PMMA film. Interestingly, flexible PMMADES films with a reduced glass transition temperature (Tg) from 73.36 °C (PMMA) to 55.38 °C were obtained. This is due to the ability of DES to act as a plasticizer by forming interactions with PMMA, as confirmed by FTIR analysis. In addition, the incorporated DES also results in a reduction in the number of crystalline grains, as observed from their optical micrographs. This is due to the increment in amorphous content, as proven by XRD analysis, which shows a reduction in crystallite size from 1.20 nm (PMMA) to 1.12 nm upon the addition of DES. Also, this study found that the PMMADESI system, which involved the incorporation of ChCl: 1,2-BD (DESI), exhibited the highest ionic conductivity (∼10−8 S cm−1) and lowest value of Tg (55.38 °C). This was due to the closest position of the hydroxyl group in 1,2-BD, which contributes to the greater disorderliness and wider ion distribution of the PMMA matrix.