Semi-interpenetrating polymer networks based on polyacrylamide and poly(itaconic acid)

Abstract

The effect of pH and temperature on the equilibrium swelling properties of PIA/PAAm semi-IPNs were investigated.Semi-IPNs based on polyacrylamide (PAAm) and poly(itaconic acid) (PIA) were prepared by two different techniques, by polymerizing itaconic acid in the presence of polyacrylamide gel (Semi-IPNs-l) and by making the polyacrylamide gel in the presence of previously synthesized poly(itaconic acid) (Semi-IPNs-ll), with different PIA/PAAm mass ratios. The equilibrium swelling degree of an ionic network depends very much on the concentration of ionisable groups. The addition of a small amount of itaconic acid dramatically changes the swelling behavior of PAAm. Increase of the ionic monomer (IA) produces swelling degrees that increase to a high extent when the pH of the buffer solution is higher than the nominal pKa values of the acid groups. Gels with higher IA content swell less than PAAm gels in low pH buffers. At low pH, when complexation due to hydrogen bonding occurs between the carboxylic groups and amide groups of acrylamide, the polymer network collapses and the swelling ratio is low. The presence of hydrogen bonds in the complexes causes additional constraints in the network, acting as a physical crosslinking and makes the network less hydrophilic, because the carboxylic groups on the PIA are occupied in the complexes. As opposed to this, the equilibrium swelling degrees change very little with pH of the solution in nonionic PAAm gel.Hydrogels exhibit continuous changes in water content as a function of temperature. The swelling degree increases with increasing temperature due to gel expansion upon warming.

U ovom radu sintetisane su semi-interpenetrirajuće mreže (semi-IPM) na bazi poliakrilamida (PAAm) i poli(itakonske kiseline) (PIK). Korišćene su dve različite tehnike sinteze sa različtim masenim odnosom komponenata u polaznoj smeši. Mreže su karakterisane merenjem ravnotežnog stepena bubrenja u puferskim rastvorima različite pH vrednosti, od 2.24 do 8.09, kao i na različitim temperaturama, pri čemu je temperatura varirana od 10 do 54°C. Povećanjem koncentracije itakonske kiseline u mreži povećava se sadržaj karboksilnih grupa i bubrenje pri višim pH vrednostima, dokje pri nižim pH bubrenje semi-IPM mart je u odnosu na cist PAAm gel. Poredenjem vrednosti ravnotežnih stepena bubrenja uočava se da u kiseloj sredini semi-IPM-l vise bubre u odnosu na semi-IPM-ll, dok je u baznoj sredini uočeno suprotno ponašanje. Pri porastu temperature semi-IPM dolazi do porasta stepena bubrenja.