Thermoresponsive and co-nonsolvency behavior of poly(N-vinyl isobutyramide) and poly(N-isopropyl methacrylamide) as poly(N-isopropyl acrylamide) analogs in aqueous media

Abstract

Sets of the nonionic polymers poly(N-vinyl isobutyramide) (pNVIBAm) and poly(N-isopropyl methacrylamide) (pNIPMAm) are synthesized by radical polymerization covering the molar mass range from about 20,000 to 150,000 kg mol−1, and their thermoresponsive and solvent-responsive behaviors in aqueous solution are studied. Both polymers feature a lower critical solution temperature (LCST) apparently of the rare so-called type II, as characteristic for their well-studied analogue poly(N-isopropyl acrylamide) (pNIPAm). Moreover, in analogy to pNIPAm, both polymers exhibit co-nonsolvency behavior in mixtures of water with several co-solvents, including short-chain alcohols as well as a range of polar aprotic solvents. While the cloud points of the aqueous solutions are a few degrees higher than those for pNIPAm and increase in the order pNIPAm < pNVIBAm < pNIPMAm, the co-nonsolvency behavior becomes less pronounced in the order pNIPAm > pNVIBAm > pNIPMAm. Exceptionally, pNIPMAm does not show co-nonsolvency in mixtures of water and N,N-dimethylformamide. Graphical Abstract

Cosolvent incorporation modulates the thermal and structural response of PNIPAM/silyl methacrylate copolymers

“…In general, DMF in PNIPAM/water systems is considered to be a chaotropic agent, 41,42,69 or structure breaker; however, at low concentrations, DMF preferentially interacts with the polymer chains to effectively stabilize the hydrated polymer conformation. 28,41 This change in behavior results in a non-monotonic T CP in the water-rich portion of the polymer/water/DMF phase diagram (Fig. 7b).…”

“…Aqueous PNIPAM exhibits a type II LCST behavior, where this critical temperature is largely insensitive to both polymer concentration and molecular weight. 28 This lack of transition temperature tunability for aqueous PNIPAM homopolymer limits its utility for applications requiring responsiveness outside of a few-degree range.…”

Thermoresponsive Polymers under Pressure with a Focus on Poly(N-isopropylacrylamide) (PNIPAM)

“…43 Tuning the phase behavior by pressure allows the role of nonspecific (e.g., van der Waals vs hydration) interactions to be assessed and may explain why cononsolvency is not present in all thermoresponsive systems, such as PNIPMAM in H 2 O/DMSO. 118…”

“…For instance, PNIPAM in H 2 O/DMSO exhibits LCST behavior at low and UCST behavior at high cosolvent concentrations (Figure a and b) . Tuning the phase behavior by pressure allows the role of nonspecific (e.g., van der Waals vs hydration) interactions to be assessed and may explain why cononsolvency is not present in all thermoresponsive systems, such as PNIPMAM in H 2 O/DMSO …”

Micellar Solutions of PMMA-b-PNIPAM in Water/Methanol Mixtures: Effect of Temperature on the Micellar Size, Core–shell Structure, and Interaction

“…In the case of thermoresponsive polymers exhibiting a lower critical solution temperature (LCST) in aqueous solution, the particular cononsolvency phenomenon refers to the reduction of polymer solubility, i.e., a reduction of the cloud point temperature, T CP , upon addition of a cosolvent, which itself is a good solvent for the polymer. − Cononsolvency has been observed for a few thermoresponsive polymers in aqueous solution, and in the case of those bearing amide moieties as hydrophilic groups, for a broad range of cosolvents. − Below the cloud point temperature in neat water, the polymer exhibits a coil-to-globule transition with increasing cosolvent fraction and, at higher cosolvent fraction, a globule-to-coil transition, i.e., re-entrant behavior. Adding a specific amount of cosolvent is thus an attractive alternative for inducing the chain collapse to the increase of the temperature above T CP .…”