Synthesis and characterization of poly(N-isopropylmethacrylamide-co-N-isopropylacrylamide) copolymers

Abstract

Copolymeric hydrogels of poly(N-isopropylmethacrylamide-co-N-isopropylacrylamide), p(NIPMAM/NIPAM), are synthesized by radical polymerization of N-isopropylmethacrylamide (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 o 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 o 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.

Intelligent Poly(N-Isopropylmethacrylamide) Hydrogels: Synthesis, Structure Characterization, Stimuli-Responsive Swelling Properties, and Their Radiation Decomposition

“…The discrete differences in the intensity and width of the absorption bands in the spectra of the synthesized homopolymers were due to the cross-linking reaction and the formation of hydrogels, as well as to the different mole fraction of the EGDM cross-linker. The results of the FTIR analysis are in agreement with the literature data [3,21,44,45].…”

“…Bending vibrations in the plane of a vinyl group, δ( =C-H) in the FTIR spectrum of NiPMAm produced the band at 1465 cm −1 , while out of plane bending, γ(=C-H), whose wavenumber and position depend on the substitution of the double bond, produced bands at 940 and 885 cm −1 . In the wavenumbers range of 1000-650 cm −1 , bands of C-H bending vibrations out of the γ(C-H) plane of the isopropyl group occurred [44]. Additionally, in this wavenumber range, the bending vibrations out of the γ(N-H) plane from the N-H group occurred, and in the FTIR spectrum of NiPMAm, the bands with maxima at 833 and 658 cm −1 originated from these vibrations.…”

“…The acceptable limits for the amount of residual methyl methacrylate in dental materials should be in the range of 1%-3% [46]. These residual amounts of the NiPMAm monomer were within acceptable limits for the p(NiPMAm) samples with 2.0, 2.5, and 3.0 mol% of EGDM, because monomers are toxic in much higher amounts [43,44]. The analyzed methanol extract samples after synthesis did not show any residual amount of the cross-linker EGDM, which indicates that the total EGDM amount reacted during the p(NiPMAm) polymerization process.…”

“…The stretching vibrations of the dC-O bond produce a band with a absorption maximum at 1154 cm −1 . The absorption band with the maximum at 1636 cm −1 originated from the absorbance of the C=C bond [44]. In the FTIR spectra of Figure 2c, a series of synthesized poly(N-isopropylmethacrylamide) homopolymer hydrogels with 1.5, 2.0, 2.5, and 3.0 mol% of EGDM are presented.…”

“…The similarity of the thermosensitive monomers of N-isopropylmethacrylamide and N-isopropylacrylamide allows their copolymers to achieve a sharp phase transition under physiological conditions. Recently, this research team published an article about copolymeric poly(N-isopropyl methacrylamide-co-N-isopropylacrylamide) hydrogels synthesized by radical polymerization [44]. These negatively thermosensitive cross-linked p(NiPMAm/NiPAm) hydrogels were structurally characterized, and their swelling behavior was investigated in relation to the temperature and pH value of their solution.…”