A novel poly(N-isopropylacrylamide-co-N-hydroxymethyl acrylamide) gel: preparation in the absence/presence of a pore-forming agent and characterization

Abstract

Poly(N-isopropylacrylamide) (PNIPAM) homopolymer gel and copolymer gels of N-isopropylacrylamide (NIPAM) and N-hydroxymethyl acrylamide (NHMAAM) were prepared in the absence/presence of a pore-forming agents, poly(ethylene glycol) (PEG) (PEG 400 or PEG 2000) using N,N'-methylenebisacrylamide (NMBA) as a crosslinker in aqueous solution at 4 degrees C. The chemical structures and microscopic morphologies of PNIPAM and P(NIPAM-co-NHMAAM) copolymer gels were investigated by FT-IR and SEM (scanning electron microscopy), respectively. The effects of initial monomer concentration (0.5 and 1 M), the contents of crosslinker (0.25 and 1%) and comonomer (1-3 mol%), the absence/presence of pore-forming agent in the feed, and the molecular weight of pore-forming agent on the compressive elastic moduli and equilibrium swelling values (ESVs) of both polymers were investigated. While the use of a pore-forming agent during the polymer synthesis favored the formation of porous gels and increased the swelling values, it led to decrease in the compressive elastic moduli of PNIPAM and P(NIPAM-co-NHMAAM) gels. The swelling values of gels, which were prepared at high monomer (1 M) and crosslinker (1 %) contents, were not dependent on the comonomer NHMAAM incorporation to PNIPAM, the use of pore-forming agents, and the use of former and latter parameters together. The twice increase in initial monomer concentration at low NMBA (0.25%) content highly enhanced the elastic moduli of PNIPAM. One mol% NHMAAM incorporation into PNIPAM especially at low monomer (0.5 M) and crosslinker (0.25%) contents made the highest increase (4.7 times) in the elastic moduli of gel, and further increase in the NHMAAM content of gel decreased the moduli of gels at all crosslinker and monomer concentrations. It was concluded that the increase in the elastic moduli of copolymer gels with 1 mol% NHMAAM, which were prepared at low crosslinker and monomer concentrations, can be attributed to the increase in crosslinking through the condensation reaction between N-methylol groups or N-methylol and -NH groups in NHMAAM and NIPAM. Copyright (C) 2008 John Wiley & Sons, Ltd.