Thermoresponsive release from poly(Glu(OMe))-block-poly(Sar) microcapsules with surface-grafting of poly(N-isopropylacrylamide).

Thermoresponsive microcapsules were prepared by grafting poly(N-isopropylacrylamide) (PNIPAAm) on the surface of polypeptide (poly(Glu(OMe))-block-poly(Sar) microcapsules. Naked poly(Glu(OMe)-block-poly(Sar) microcapsules were partly hydrolysed with NaOH to remove methyl groups and newly formed carboxyl groups were used to anchor polyallylamine having 4,4'-azobis(4-cyanovaleric acid) groups. Graft polymerization of N-isopropylacrylamide at the microcapsule surface was initiated by photo-cleavage of the azo groups. Microscopic examination showed that a homogeneous dense skin layer of PNIPAAm was formed on the surface of microcapsule at 40 degrees c, while the skin layer became loose when the temperature was lowered to 25 degrees C. Dextran release from the microcapsule was faster below the lower critical solution temperature (LCST) of PNIPAAm than that above it. When the temperature changed across the LCST, a reversible, thermoresponsive release from the microcapsule was observed. Notable, the transition of the release rate by changing the temperature occurs quickly in a narrow temperature range.