A new, highly stable cationic-thermosensitive microgel: Uniform isopropylacrylamide-dimethylaminopropylmethacrylamide copolymer particles

New monodisperse, thermosensitive, cationic microgel particles up to 1930 ± 56 nm in size were obtained by the dispersion copolymerization of N-isopropylacrylamide (NIPA) and N-3-dimethyl-aminopropylmethacrylamide (DMAPM). In the developed protocol, an amide based comonomer, DMAPM was tried as a new alternative material for introducing positive charge to the thermosensitive microgel. Poly(NIPA-co-DMAPM) microgel exhibited pH-sensitivity and the particle size linearly decreased with increasing pH. Poly(NIPA-co-DMAPM) microgel synthesized without making any pH adjustment in the aqueous medium exhibited colloidal stability between pHs 3 and 10 while similar cationic microgels were reported to be unstable at pHs higher than 6. The stronger cationic character of selected comonomer originated from its amide based structure (i.e. higher pKa of DMAPM) provided higher colloidal stability to the poly(NIPA-co-DMAPM) microgel. teraction of poly(NIPA-co-DMAPM) particles with albumin was investigated by using plain poly(NIPA) particles as control material. The albumin adsorptions up to 96 mg/g particles were obtained at the isolelectric point via the reversible complexation between carboxyl groups of albumin and protonated dimethylamino groups on the particles. The albumin adsorption was effectively controlled by changing the surface characteristics of poly(NIPA-co-DMAPM) particles by both switches (i.e. pH and temperature). The hydrophilicity increase of particles induced by temperature decrease and the deprotonation of dimethylamino groups with increasing pH provided nearly quantitative albumin desorption from the poly(NIPA-co-DMAPM) particles. These advantages make poly(NIPA-co-DMAPM) microgel as a promising material for the development of new surface related biotechnological applications.