Preparation and properties of thermosensitive hydrogel microcapsules

Temperature-sensitive hydrophilic gel microcapsules have been newly prepared. That is, poly (L-lysineisopropylamide-terephthalic acid) microcapsules containing water have been obtained by an interfacial polymerization at a water/oil interface between L-lysineisopropylamide and terephthaloyldichloride. The microcapsule changes its size between 33 and 35 degrees C. Under 33 degrees C, the microcapsules are fully spherical and can be redispersed in distilled water, while are aggregated above 35 degrees C. The microcapsules, which are observed to show aggregation above 33 degrees C, can be redispersed by decreasing temperature within a few second. The thermosensitive morphological changes of the microcapsules are thus reversible. Also, it has been shown that the permeability of sodium chloride through the microcapsule membrane changes remarkably between 33 and 35 degrees C, while it is kept almost constant independent of temperature between 25 and 33 degrees C or between 35 and 55 degrees C. The permeability of solutes is higher under 33 degrees C than that above 35 degrees C. Such thermosensitive properties result from the fact that the polymer membrane has isopropylamide groups. That is, L-lysineisopropylamide has a chemical structure similar to N-isopropylacrylamide, the polymer of which, poly (N-isopropylacrylamide), is a thermosensitive hydrogel having its phase transition temperature around 33 degrees C.