Release property of microgels formed by electrostatic interaction between poly( N ‐isopropylacrylamide‐ co ‐methacrylic acid) and poly( N ‐isopropylacrylamide‐ co ‐dimethylaminoethylmethacrylate)

Microgels were prepared by taking advantage of electrostatic interaction between poly(N‐isopropylacrylamide‐ co ‐methacrylic acid) and poly( N ‐isopropylacrylamide‐ co ‐dimethylaminoethylmethacrylate). The maximum interaction, investigated by measuring the size of complex and the turbidity of the mixture, took place at pH = 6.5. The microgel prepared at pH = 6.5 using the copolymer ratio of 1/1 (w/w) was globular on scanning electron microscopy, and the size was a few to tens of micrometer. The phase transition of the microgel, observed by turbidometry and differential scanning calorimetry, occurred around 31°C. % Release, in 24 h at room temperature, of FITC‐dextran from the microgel was higher under an acidic (64% at pH = 4.0) and an alkali condition (69 % at pH = 9.0) than the % release at pH = 6.5 (41%). The disintegration of microgels would be responsible for the higher % release. The % releases, in 24 h at pH = 6.5, were lower at higher temperatures (53% at 35°C, 50% at 40°C) than at lower temperatures (71% at 25°C, 61% at 30°C). The suppressed release at higher temperatures is possibly due to the skin formation on the surface of microgel. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012