Abstract
Copolymeric hydrogels of poly(N-isopropylmethacrylamide-co-N-isopropylacrylamide), p(NIPMAM/NIPAM), are synthesized by radical polymerization of N-isopropylmethacryl-amide (NIPMAM) and N-isopropylacrylamide (NIPAM) monomers by using the cross-linker ethylen glycol dimethacrylate (EGDM). The synthesized copolymeric p(NIPMAM/NIPAM) hydrogels, starting monomers and the cross-linker were structurally characterized by using Fourier transform infrared spectroscopy (FTIR). The amounts of residual reactants in the synthesized hydrogels were determined by high-pressure liquid chromatography (HPLC). Swelling of p(NIPMAM/NIPAM) hydrogels was investigated in relation to the temperature and pH value of the solution. The obtained values of residual monomer quantities are within acceptable limits and in the range from 2.69 to 5.25 mg g-1 for NIPMAM and 14.55 to 30.80 mg g-1 for NIPAM. The synthesized p(NIPMAM/NIPAM) hydrogels are negatively thermosensitive. The most common mechanisms of transport of a swelling solution in p(NIPMAM/NIPAM) hydrogels are polymer chain relaxation, (Case III), and the anomalous type of diffusion (non-Fickian diffusion). The maximal equilibrium swelling degree of 51.19 was reached by the p(NIPMAM/NIPAM) hydrogel with 1.5 mol% of EGDM at the temperature of 25?C and pH 4, whereas the lowest one of 0.98 was exhibited by the hydrogel with 3 mol% of EGDM at the temperature of 80?C and pH 7. Due to their low content of residual reactants and a satisfactory degree of swelling at various pH values, synthesized p(NIPMAM/NIPAM) hydrogels can be applied as carriers for the controlled release of pharmaceutically active substances.
Highlights
Hydrogels are chemically or physically cross-linked hydrophilic polymer networks capable of absorbing large amounts of water or biological fluids [1,2,3]
The synthesized copolymeric p(NIPMAM/NIPAM) hydrogels, starting monomers and the cross-linker were structurally characterized by using Fourier transform infrared spectroscopy (FTIR)
P(NIPMAM/NIPAM) hydrogels were synthesized by radical polymerization at the molar ratio of monomers 40/60 with ethylen glycol dimethacrylate (EGDM) as a cross-linker in the concentrations of 1.5, 2 and 3 mol%
Summary
Hydrogels are chemically or physically cross-linked hydrophilic polymer networks capable of absorbing large amounts of water or biological fluids [1,2,3]. The resulting changes are reversible, i.e. hydrogels return to their original state after removing the environmental stimuli [7,8,9]. Due to this feature, certain hydrogels are known as ‘smart’ materials [7,10,11]. Swelling of hydrogels is influenced by the hydrogel composition, polymer and solvent compatibility, a degree of cross-linking, temperature
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