Stimuli-responsive polymer utilizing keto-enol tautomerization and stimuli-responsive separating material and chemical-releasing capsule comprising the same

#The present invention relates to an excellent stimuli-responsive polymer derivative which can be used for drug delivery system (DDS), chemovalve, various separating agents, catheter, artificial muscle, etc.

#In recent years, stimuli-responsive polymers have been widely used for drug delivery system (DDS), various separating agents, catheter, artificial muscle, chemovalve, etc. and thus have been of growing importance. For example, JP-A-8-103653 (The term “JP-A” as used herein means an “unexamined published Japanese patent application”) discloses a polymer which changes in its higher order structure to swell or shrink in an aqueous solution by the action of heat, light or by a change in pH or potential as a stimuli-responsive polymer. Specifically, acrylamide or methacrylamide derivatives such as poly-N-isopropylacrylamide, N,N-diethylacrylamide and N-isopropylmethacrylamide, and vinylethers such as vinyl methyl ether are disclosed as a polymer having an upper critical solution temperature (UCST) or a lower critical solution temperature (LCST) with respect to water, which swells or shrinks in response to a temperature change.

#Although these known polymers which swell or shrink in response to a temperature change are described as having an upper critical solution temperature (UCST) or a lower critical solution temperature (LCST), they all have, in fact, a lower critical solution temperature (LCST). In other words, at a temperature of not lower than the lower critical solution temperature, these polymers reversibly undergo agglomeration of polymers that renders themselves insoluble in water. On the contrary, at a temperature of not higher than the lower critical solution temperature, these polymers can be dissolved in water. For example, poly-N-isopropylacrylamide (PNIPAM), which is applied to DDS, etc. at present, has a lower critical solution temperature of 32° C. in an aqueous solution. When this polymer is allowed to gel, it reversibly undergoes swelling and shrinkage depending on the temperature developed by heat.

#The present invention will be further described hereinafter.

#In accordance with the first aspect of the present invention, as mentioned above, by properly making a molecular design using keto-enol tautomerization, a stimuli-responsive polymer derivative having an upper critical solution temperature (UCST) or a stimuli-responsive polymer derivative which undergoes phase transition in accordance with a change in hydrogen ion concentration or an addition of an organic solvent can be easily obtained.

#For example, a polymer derivative containing a substituent component represented by the following general formula (8) may be preferably used: