Hydrogen-Bonding Effects on the Dynamic Swelling of P(N-iPAAm-co-MAA) Copolymers. A Case of Autocatalytic Swelling Kinetics

Abstract

The swelling kinetics of a series of P(N-iPAAm-co-MAA) copolymers and their P(N-iPAAm) and P(MAA) homopolymers previously soaked under different acidic and neutral conditions have been studied at pH 7 to probe the hydrogen-bonding ability of comonomers. Experimental data analysis has revealed that although the state due to the previous soaking pH does not exert any influence on the equilibrium swelling value of copolymers, it exerts a strong influence on their swelling kinetics. Copolymers gels ranging in composition between 30 and 70 mol % of N-iPAAm previously soaked under acidic conditions exhibit, when subsequently immersed in water at a neutral pH, sigmoidal swelling curves. This behavior has been interpreted according to an autocatalytic mechanism, suggesting that cooperativity on the hydrogen bond disruption controls the swelling behavior. The dynamic swelling of these hydrogels under pH 7 after soaking at this same pH is in very good agreement with a second-order kinetics. This fact corroborates that anomalous features found on the swelling dynamics of these copolymers are related to the strong hydrogen-bonding arrangement between both comonomeric units as well as to the hydrophobicity strongly enhanced by intra-or/and interchain hydrogen bonding.

pH-responsive hydrogel membranes based on modified chitosan: water transport and kinetics of swelling

“…These results suggest that Schott , s second-order kinetic equation is adequate to describe the whole swelling process of chitosan hydrogel membranes in buffer solutions. Our results are consistent with the statements of others that the swelling kinetics behaviour of ionic hydrogels (anionic and cationic hydrogels) is in good accordance with Schott , s second-order diffusion kinetics [49][50][51][52][53][54][55]. Table 2 shows that values of apparent swelling rate constant for Ch/GA and Ch/GA/SA membranes are of the same order of magnitude for acidic and neutral swelling media but they increase for alkaline solutions.…”

Composite Superabsorbent Hydrogel of Acrylic Copolymer and Eggshell: Effect of Biofiller Addition

“…It can be observed that almost all of the experimental points lie on the respective straight lines for each hydrogel. However, the values did not fit the straight lines in the first few minutes, suggesting a different kinetics order, probably a first-order process, as suggested by Diez-Peña et al 35 A new plot (not shown) was obtained without the initial points and a better fit and linear correlation coefficients (R 2 ) were observed. The R 2 value for the straight line for Pam-Ac increases from 0.9992 to 0.9995.…”

“…In general, the swelling follows a first-order or a secondorder kinetics. 35 The second-order rates may be obtained from the well-known equation…”

The influence of the copolymer composition on the diltiazem hydrochloride release from a series of pH-sensitive poly[(N-isopropylacrylamide)-co-(methacrylic acid)] hydrogels

“…24,25 Copolymer composition (Table 1) was determined by elemental analysis performed using a CHN EA 1108-elemental analyzer (Carlo Erba Instruments, Milano, Italy). Because the previous swelling history was shown to have strong influence on the swelling behavior, 26 samples from synthesis were soaked under acidic medium (pH 1.2) and dried in a vacuum oven at 60°C for 24 hours in order to obtain homogeneous samples with a controlled morphology history.…”

“…10,[16][17][18][19][20][21][22][23][24][25][26] These copolymers possess a wide range of swelling characteristics depending on composition and previous swelling history, [24][25][26] which potentially allow hydrogels to be obtained for specific uses. Because of the N-iPAAm moiety, these copolymers are able to respond to temperature changes, while the ionizable carboxyl group provides pH sensitivity.…”