Superabsorbent nanohydrogels of poly (N-isopropyl acrylamide –co-itaconic acid) grafted on starch: Synthesis and swelling studies

Poly(N-isopropylacrylamide) (PNIPAAm) hydrogels are attracting more and more interest in biomedical applications because they exhibit a well-defined lower critical solution temperature (LCST) in water around 31–34◦C which is close to the body temperature. Natural polymers like starch are of considerable interest in the fields of biotechnology, biomedical engineering, and pharmaceutical controlled release devices. In the present work, biodegradable and thermosensitive superabsorbent nanohydrogels were synthesized by graft copolymerization of poly N-isopropyl acrylamide (PNIAAm)/itaconic acid (IA) onto starch via free radical copolymerization in the absence of chemical crosslinker agent. The starch grafted nanohydrogels were characterized by FT-IR and thermal gravimetric analysis (TGA). Dynamic light scattering (DLS) showed 60-100 nm size distribution for the synthesized hydrogels. TGA studies indicated that grafting of poly(NIPAAm-co-IA) onto starch leads to an overall improvement in the thermal stability. The effect of different amount of ammoniumpersulfate as the polymerization initiator, on the water absorption of the superabsorbent polymers, pH sensitivity and thermal behaviors were investigated. The water absorption of the grafted copolymer synthesized by 10.0 wt% APS gave the highest water absorption degree of 45 g /g. Hydrogels were sensitive to environmental pH. So, the swelling behaviors of the superabsorbent nanohydrogel were studied at various pH values between 3 and 12, at room temperature. Under acidic pH values (3), most of the carboxylate anions are protonated, so the main anion–anion repulsive forces are eliminated and consequently swelling values are decreased. At higher pH values, some of the carboxylate groups are ionized and the electrostatic repulsion between COO- groups causes an enhancement of the swelling capacity. The obtained nanohydrogels may potentially be used in biomedicine, pharmaceutics and controlled delivery of bioactive agents.

کلیدواژه ها:

Stimuli-sensitive ، polymers ، Multicompartmental systems .Volume phase transition temperature . Drug delivery systems