pH‐responsive semi‐interpenetrating networks hydrogels of poly(acrylic acid‐acrylamide‐methacrylate) and amylose. I. Synthesis and characterization

Abstract

The semi-interpenetrating networks gels of hydrophobically-modified poly(acrylic acid-acrylamidemethacrylate) and amylose were prepared using 4,4 0 -bis(methacryloylamino) azobenzene as a crosslinker. Investigation of mechanical strength of gels showed that the equilibrium elastic modulus G changed from 12.4 to 32.9 g/cm 2 with increasing the contents of amylose in the case of low content of crosslinker. The swelling behavior of gels indicated that the aggregation of the hydrophobic groups of hydrogels could be destroyed by expanded amylose and the electrostatic repulsion between the charged À ÀCOO À groups because of the ionization of the carboxylic groups in pH 7.4 buffer solutions. The hydrophobicity and flexibility of the side chain, the entanglement extent of the amylose, and the ionization of carboxyl groups in the gels greatly affected the swelling rates and swelling ratios. Investigations of swelling/deswelling periodically in pH 2.2 and 7.4 media indicated that the semi-IPN gel was more pH-sensitive than the nonsemi-IPN gel.

Triply‐responsive (thermo/light/pH) copolymeric hydrogel of N‐isopropylacrylamide with an azobenzene‐containing monomer

“…The expansion of electrostatic repulsion between the charged COO − groups destroyed the hydrophobic microdomain formed by the hydrophobic interactions of the side chains 36. On the contrary, in pH 2 media, carboxyl groups were not ionized and existed as COOH, which increased the hydrophobic interactions and hydrogen bonding between the carboxylic and amide groups of the copolymer chains, so the hydropilicity decreased and the equilibrium swelling ratio was lower which is in accord with other reports 37. As a result, the value of swelling ratio was much higher than that of in pH 2.…”

Removal of Cationic Dyes from Aqueous Solution by Hydrophobically Modified Poly(acrylic Acid) Hydrogels

“…This phenomenon can be explained by considering that at pH > 4.28 (the pK a of poly(acrylic acid): $4.28) [18] , the most of the carboxylic groups are ionized and interacted with the cationic dye molecules, which leads the cationic dye adsorption to stabilization. At lower value of pH (acid condition), the hydrogels are in compact collapsed status (noionized status) due to the hydrogen bonding interactions between the carboxylic groups of hydrogels and hydrophobic interactions among the side chains.…”

In vitro degradation and protein release of semi‐IPN hydrogels consisted of poly(acrylic acid‐acrylamide‐methacrylate) and amylose

“…11 It implies that the drug-loaded semi-IPN hydrogel can be protected from the gastric enzyme before its entry into the colon. Figure 6 shows the release kinetics of BSA-loaded gel n4 À 1 in pH 2.2 and 7.4 buffer solutions.…”

“…10 In our previous study, we synthesized semi-IPN hydrogels consisted of poly(acrylic acid-acrylamide-alkyl methacrylate) crosslinked by azocompound and amylose and discussed their swelling behavior. 11 This type of semi-IPN hydrogel swells hard at pH 2.2 (the pH value in the stomach) and swells easily at pH 7.4 (the pH value in the colon) because of the ionization of carboxyl groups and expand of amylose chains. Amylose is a natural and nontoxic polysaccharide, which can be enzymatically degraded 10,12 together with the azo crosslinker by colonic enzymes.…”