Temperature dependence of density of polymer gels: Effects of ionizable groups in copoly(N-isopropylacrylamide/acrylic acid or sodium acrylate)–water systems

Characteristic role of crosslinker on thermally induced volumetric contraction–expansion processes in poly(N‐isopropylacrylamide) networks and water systems

“…Water was replaced at least once in a day with fresh water over a week. Subsequently, the gel pieces were sliced into discs of ∼ 5 mm in thickness and were then lyophilized by freeze‐drying method under vacuum (<10 −4 mmHg) over 36 h 14, 15, 18…”

“…When we evaluated v sp (gel)( T ) and N s (gel)( T ) for hydrogels of (A) copoly[NIPA(1‐ x )/acrylic acid ( x )(AAc)] [mean formula mass (FM)] and (B) copoly[NIPA(1‐ x )/sodium acrylate ( x )(NaAc)] (mean FM), where the mol fraction x is assumed at 0.0114 and 0.0457, we had to use mean FM of NIPA and AAc or NaAc according to the chemical composition of polymer networks. This approach clarified18 that varying states of ionizable groups on temperature produced direct effects on volumetric contraction–expansion processes in the aforementioned hydrogels of copolymer networks differing from that in hydrogel of poly(NIPA). We were able to reveal further details at nanoscale by developing a means to evaluate gel volumes solely occupied by a single minor copolymer component, i.e., AAc or NaAc residue and associated water molecules, v sp (gel)( T )(AAc or NaAc), by applying thermodynamic perturbation theory [here, the hydrogel of poly(NIPA) is an unperturbed system.…”

“…Thus, v (gel)[ionizable( x )] is the volume attributable to all ionizable groups] 19. These results revealed characteristic changes in the volumetric contraction–expansion processes near their swollen–shrunken state transitions 18…”

Synthesis and characterization of novel poly(acrylamide‐co‐acrylic acid‐co‐2‐hydroxy ethyl actylate) hydrogels: Mathematical approach in investigation of swelling kinetics and diffusion models

“…Its magnitude significantly affects the physical properties of hydrogel. The degree of swelling is an important parameter; which is directly proportional to the mesh size, number‐average molecular weight between crosslinks, whereas crosslinking density followed inverse trend with extent of swelling 26. In ionic hydrogels, network parameters may be controlled by the monomer concentration in the reacting polymerization solution and by the swelling solution pH.…”

Two-dimensional correlation ATR-FTIR studies on PEO–PPO–PEO tri-block copolymer and its phosphorylcholine derivate as thermal sensitive hydrogel systems

“…''Smart'' hydrogels which are sensitive to the temperature, ionic strength or pH value [1][2][3][4][5][6][7] have been extensively studied for their potential applications in site-specific controlled drug delivery and bio-separation [8][9][10]. Among these, the commercialized PEO-PPO-PEO tri-block copolymer named Pluronic or Poloxamer was already applied in some cases [11,12] for its well studied thermal reversible gelation properties.…”