Contrasting thermoresponsiveness of stereoisomers of a dense 1,2,3-triazole polymer carrying amide side chains

• Published in: Polymer Chemistry Vol. 14; no. 13; pp. 1488 - 1496
• Main Authors: Okuno, Koji, Miura, Junji, Yamasaki, Shota, Nakahata, Masaki, Kamon, Yuri, Hashidzume, Akihito
• Format: Journal Article
• Language: English
• Published: Cambridge Royal Society of Chemistry (RSC) 28.03.2023; Royal Society of Chemistry
• Subjects: Alkynes; Aqueous solutions; Binary mixtures; Cycloaddition; Dimethyl sulfoxide; Dimethylformamide; Isomers; Isotacticity; Phase transitions; Polymer chemistry; Polymerization; Polymers; Sol-gel processes; Stereoisomerism; Syndiotacticity; Temperature
• DOI: 10.1039/d2py01528e
• ISSN: 1759-9954

Since thermoresponsive polymers are an important class of smart polymer materials, it is an important subject of investigation to develop thermoresponsive polymers with a new polymer backbone for expanding their potential. Recently, we synthesized poly( N -ethyl- N -methyl-4-azido-5-hexynamide) (poly( ME )) by copper( i )-catalyzed azide-alkyne cycloaddition (CuAAC) polymerization as a new lower-critical-solution-temperature (LCST) type thermoresponsive polymer. In this study, we synthesized two types of stereoregular poly( ME ) ( i.e. , isotactic and syndiotactic) by CuAAC polymerization of ME dimers of the R - and R -isomers, and the R - and S -isomers, respectively, and investigated their thermoresponsive behavior. Binary mixtures of isotactic poly( ME ) ( iso -poly( ME )) with dimethyl sulfoxide (DMSO) and with N , N -dimethylformamide (DMF) underwent thermoresponsive gel-to-sol transition, in which the mixture turned from gel to sol at a certain temperature as the temperature was increased. On the other hand, aqueous solutions of syndiotactic poly( ME ) ( syndio -poly( ME )) underwent the LCST-type phase transition, in which the solution was transparent at lower temperatures whereas it became turbid at a certain temperature as the temperature was increased. Thermoresponsive behavior of stereoisomers of a dense triazole polymer was studied; mixtures of the isotactic one underwent thermoresponsive gel-to-sol transition, and aqueous solutions of the syndiotactic one underwent LCST-type phase transition.