Design of Thermoresponsive Polymers with Aqueous LCST, UCST, or Both: Modification of a Reactive Poly(2-vinyl-4,4-dimethylazlactone) Scaffold

Abstract

The synthesis and aqueous solution properties of a family of zwitterionic homo-, co-, and terpolymers derived from poly(2-vinyl-4,4-dimethylazlactone) (pVDMA) with tunable lower and upper critical solution temperatures (LCST and UCST) are presented. A RAFT-made pVDMA precursor was reacted with mixtures of zwitterionic sulfopropylbetaine (SPB) amine or sulfobutylbetaine (SBB) amine, tetrahydrofurfurylamine (THF amine), and benzylamine (Bz amine) in varying molar ratios. Products were characterized by variable temperature (VT) NMR spectroscopy, FT-IR spectroscopy, size exclusion chromatography, turbidity, and VT dynamic light scattering in order to confirm quantitative postpolymerization modification, determine molar compositions, and elucidate structure−property relationships. Polymers comprising large molar fractions of THF groups showed LCST behavior due to a polarity change of the THF-functional segments, while SPB/SBB-rich samples, including the zwitterionic homopolymers, showed UCST behavior in ultrapure water based on electrostatic polymer−polymer attractions. Binary SPB−THF copolymers were water-soluble between 0 and 90 °C for a large compositional range. Terpolymers comprising molar SPB:THF:Bz ratios of approximately 50:25:25 showed a low LCST and a high UCST (LCST < UCST) with a miscibility gap in which the SPB groups and THF groups were not fully hydrated. In the one-phase regions below the LCST and above the UCST, polymer chains were presumed to be unimerically dissolved with partially solvated domains undergoing intrachain associations. Addition of NaCl caused LCST and UCST behavior to disappear, resulting in temperature-independent solubility. Molecular insights presented herein are anticipated to aid in the development of smart materials with double LCST < UCST or UCST < LCST thermoresponsiveness.

Effect of the zwitterion structure on the thermo-responsive behaviour of poly(sulfobetaine methacrylates)

“…2 Moreover, their transition temperatures can be easily fine-tuned via their molecular structure, as they can be synthesised not only by various polymerisation methods directly from the respective monomers, 1,2 but also by copolymerisation 3,[10][11][12] or by post-polymerisation modification. 4,[13][14][15] In contrast, the number of polymers showing UCST behaviour in water is quite limited. 7,8 These polymers mostly comprise polyzwitterions, in particular of the class of polysulfobetaines.…”

“…for producing biocompatible or low-fouling materials). Only recently has interest in the UCST behaviour of polysulfobetaines gained more impetus, mostly in order to † Electronic supplementary information (ESI) available: Synthesis of tertiary amine bearing methacrylates; a enlarge the scope of the "traditional" thermo-responsive polymers with LCST behaviour 15,[24][25][26][27][28][29][30] or to obtain stimuli-responsive materials of increasing complexity. [31][32][33][34][35][36][37][38][39][40] Chemically well-defined polysulfobetaines are most conveniently prepared via free radical polymerisation of the underlying monomers.…”

“…This finding agrees with previous studies on the pair P-1/P-5, 20,29,53 and matches well with reports on analogous pairs of acrylamide-and methacrylamide-based polysulfobetaines. 15,30,71 One might be tempted to explain this observation by an increased overall hydrophobicity of the poly(ammoniobutanesulfonates) due to the additional methylene group in the spacer separating the cationic and the anionic groups of the betaine moiety. However, such a simplistic explanation seems to fall too short, because the few data available for poly(ammonioethanesulfonate) analogues indicate that their solubility in water is inferior to that of their poly(ammoniopropanesulfonate) H NMR spectra of poly(sulfobetaine methacrylate)s P-1-P-8 in D 2 O with added NaCl (solvent signal at 4.78 ppm); from top to bottom: P-1 270 , P-2 250 , P-3 230 , P-4 295 , P-5 280 , P-6 250 , P-7 260 and P-8 290 .…”

A new thermoresponsive polymer of poly(N-acryloylsarcosine methyl ester) with a tunable LCST

“…As for the tertiary amide-based polyacrylamides, it is more difficult to equip the polymers with thermoresponse than the secondary amide-based polyacrylamides due to the complexity to achieve hydrophobic-hydrophilic balance. As a result, one can easily prepare thermoresponsive polymers of the secondary amide polyacrylamides, [19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37] such as poly(N-methacryloyl-L -alanine methyl ester), 33 poly(N-acryloylglycine methyl ester) 34 , poly(N-acryloyl-Lproline methyl ester), 35 poly(N-acryloyl-L -phenylalanine methyl ester) 36 and poly(N-cyclopropylacrylamide), 37 In this work, we design and synthesize a thermoresponsive polymer, poly(N-acryloylsarcosine methyl ester) (PNASME, Scheme 1) with a tertiary amide group in the pendant. And the hydrophobic ester group was employed to counteract the hydrophilic tertiary amide group, making PNASME exhibiting a LCST-type phase transition behavior.…”

Covalently Crosslinked and Physically Stable Polymer Coatings with Chemically Labile and Dynamic Surface Features Fabricated by Treatment of Azlactone-Containing Multilayers with Alcohol-, Thiol-, and Hydrazine-Based Nucleophiles

“…Several recent reports highlight the utility of azlactone groups and the use of azlactone-functionalized polymers as reactive platforms for the design of new functional materials, surfaces, and interfaces of interest in many other contexts. 15,23,[29][30][31][32][33][34][35][36][37][38][39][40][41][42] In this current study, we sought to develop new approaches to tailor the surface and bulk properties of azlactone-containing materials using other classes of non-amine-based nucleophiles (Scheme 1). Azlactone groups are understood to react with primary alcohols and thiols under certain conditions (e.g., in the presence of a catalyst and at higher temperatures), 23,43-45 but the use of these nucleophiles to design new materials is far less developed than approaches that exploit the reactivity of azlactones with more nucleophilic primary amines.…”