Soluble−Insoluble−Soluble Transitions of Aqueous Poly(N-vinylacetamide-co-acrylic acid) Solutions

Abstract

Several poly(N-vinylacetamide-co-acrylic acid)s with various copolymer compositions have been synthesized, and their unique phase-transition behavior in aqueous salt (Na2SO4 or NaCl) solutions was investigated. Copolymers containing more than 51 mol % N-vinylacetamide (NVA) show reentrant soluble-insoluble-soluble transitions with increasing temperature. The soluble-insoluble transition temperature (T(p1)) increased linearly with increasing NVA content, whereas the insoluble-soluble transition temperature (T(p2)) was almost constant irrespective of the NVA content. Potentiometric titration of the copolymer solutions suggested that the acrylic acid (AA) carboxyl groups form hydrogen bonds with the NVA amide groups even under soluble conditions. Dehydration of the NVA amides and their consequent hydrogen bonding with the AA carboxyl groups during the soluble-insoluble transition process was indicated by FTIR measurements. Addition of salt (Na2SO4 or NaCl) to the aqueous media reduces the solvent quality and enhances the intra- and interchain interactions of the copolymers. Thus, T(p1) was observed to decrease and T(p2) was observed to increase with increasing salt concentration. However, the addition of urea to the media reverses the concentration dependence of T(p1) and T(p2) by disturbing the intra- and interchain interactions of the copolymers.

Thermoresponsive Diblock Copolymer with Tunable Soluble–Insoluble and Soluble–Insoluble–Soluble Transitions

“…This phenomenon is attributed to the modification of the competition between intra‐ and interchain interactions such as hydrogen bonding and hydrophobic interactions, by the added salts 22. This salt‐concentration dependence of the temperature range is similar to that in the poly( N ‐vinylacetamide‐ co ‐acrylic acid) in Na 2 SO 4 ‐containing aqueous media 23. This result indicates that the S‐I and S‐I‐S transitions of the mPEG‐ b ‐PDMAEMA aqueous solutions can be easily tuned by the addition of salts.…”

Transformer Hydrogels: A Review

“…Consequently, a focus is on creating nonionic UCST hydrogels and also dual LCST‐ and UCST‐responsive hydrogels . For example, by combining AAm or AAc with NIPAM, diethylacrylamide or vinylacetamide, hydrogels showing both LCST and UCST responsiveness can be formed. Other examples of hydrogels showing dual thermoresponsivity are copolymers of poly(ethylene glycol) and poly(acrylamide‐ co ‐acrylonitrile), and poly(imidazoled glycidyl methacrylate‐ co ‐diethyleneglycol methyl ether methacrylate) .…”

Tunable Dual‐Thermoresponsive Phase Behavior of Zwitterionic Polysulfobetaine Copolymers Containing Poly(N,N‐dimethylaminoethyl methacrylate)‐Grafted Silica Nanoparticles in Aqueous Solution

“…The dual thermoresponsivities of the aforementioned copolymers arise from electrostatic interactions (UCST) and hydrophobic interactions (LCST) in aqueous solutions. In contrast, the soluble‐insoluble‐soluble transitions of poly(acrylic acid)‐based random copolymers are attributed to intrachain hydrogen‐bonding interactions (UCST) and a moderate hydrophobicity (LCST) . Mori et al synthesized proline‐based block copolymers with both an UCST and a LCST.…”