Poly (acrylamide-co-methyl methacrylate) hydrogels of different ratios were prepared by using chemical and physical crosslinks to study the effect of nature of crosslinks on swelling behavior of hydrogels. The chemically crosslinked gels were prepared by using NNЈ-methylene bis acrylamide, while physically crosslinked hydrogels were prepared by precipitation polymerization method, using dioxane as solvent. Detailed swelling kinetics such as swelling ratio, transport exponent n, diffusion coefficient D and the effect of pH on equilibrium swelling studies. The study revealed that the nature of crosslinks alter the swelling characteristics of the hydrogel. In chemically crosslinked hydrogels the water transport is Fickian in nature, while in the case of the physically crosslinked hydrogels the water transport mechanism is anomalous indicating major change in relaxation mechanism due to nature of crosslinks. The results also indicate that with increasing acrylamide content the swelling ratio of the hydrogels were also increased, but the transport exponent n remains nearly constant.

ABSTRACT:A modified poly(acrylamide-co-methyl methacrylate-co-vinyl amine-co-acrylic acid) [poly(AAm-co-MMA-co-VAm-co-AAc)] hydrogel was prepared by the Hofmann degradation of poly(acrylamide-co-methyl methacrylate) [poly(AAm-co-MMA)] copolymer. The hydrogel was characterized by Fourier transform infrared (FTIR) spectroscopy, differential scanning calorimetry (DSC), thermogravimetric analysis, and swelling studies. Matrices of this hydrogel with acetaminophen were prepared for application in controlled release. The physical state of the drug (acetaminophen) and its interaction with the modified polymeric hydrogel were examined in hydrogel-acetaminophen matrices with DSC. The acetaminophen in the matrices (with more than 10% drug) exhibited distinct melting endotherms because of their crystalline state. The peak temperature of these endotherms was lowered and the peaks were broadened as the concentration of acetaminophen decreased. The melting enthalpy of acetaminophen in various matrices when plotted as a function of acetaminophen concentration yielded a straight line with an intercept of 142 mg/g of matrix, which was the solubility of acetaminophen in the hydrogel at its melting temperature. FTIR spectroscopy investigations confirmed that hydrogen bonding occurred between the modified polymeric hydrogel and acetaminophen. Scanning electron microscopy studies revealed the presence of acetaminophen drug crystals of various shapes, sizes, and roughness on the surface, depending on acetaminophen loading. The controlled release of acetaminophen was tested in vitro; 67.10 and 37.2% cumulative releases were obtained for the poly(AAm-co-MMA) and poly(AAm-co-MMA-coVAm-co-AAc) hydrogel matrices, respectively. The acetaminophen release percentage for the modified hydrogel was low because of secondary interactions with acetaminophen.

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Acrylamide-co-methyl methylacrylate (AAm-coMMA) copolymeric hydrogels of different ratios were prepared by using chemical and physical crosslinks. The physically crosslinked hydrogels were prepared by solution polymerization using benzoyl peroxide as an initiator, while the chemically crosslinked hydrogels were prepared by using N,N-methylene bisacrylamide (N,N-MBA) as crosslinking agent. This copolymeric hydrogel was further modified by Hofmann degradation to improve its swelling behaviour. 1 H-nuclear magnetic resonance (1 H-NMR), Fourier transform infra-red spectroscopy (FT-IR), differential scanning calorimetry (DSC) and elemental analysis have been used to characterize the copolymeric gel. Elemental analysis has been used to evaluate the copolymer composition. The influence of environmental conditions such as temperature and pH value on the swelling behaviour of these copolymeric gels was investigated. Results showed that the hydrogels exhibited different equilibrium swelling ratios at different pH and temperature of swelling medium. The temperature and pH sensitivities of these gels also depended on the AAm content in the copolymeric hydrogels. These hydrogels exhibited 2135% swelling at 60 • C, which was reversible and very good dimensional stability was mentioned. This was due to hydrolysis of amide groups could be hydrolyzed to form negatively charged carboxylate ion in hydrogels in response to an external pH and temperature variation.