Inversion of polymer micelles formed from double thermo-sensitive diblock copolymers

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We have prepared several double thermosensitive diblock copolymers consisting of poly(sulfobetaine) and poly(N-alkyl acrylamide) blocks, which have a upper critical solution temperature(UCST)and a lower critical solution temperature(LeST), respectively, by RAFT(Reversible Addition Fragmentation chain Transfer)process using 4-cyanopentanoic acid dithiobenzoate as a chain transfer regent.The block copolymers form micelles that exhibit a core-corona inversion simply depending on temperature, that is, poly(sulfobetaine)-core and poly(N-alkyl acrylamide)-core micelles are formed below the UCST and above the LCST, respectively.IR spectroscopic investigation on the micellization of a diblock copolymer consisting of poly(3-dimethyl(methacryloyloxyethyl) ammonium propane sulfonate)(PdMMAEAPS) and poly(N, N-diethylacrylamide)s (PdEA) blocks showed that the v(C0) and v(S0_3) bands of the PdMMAEAPS block and the amide I band of PdEA block critically changes at the UCST and LCST, respectively.The result indicates that segmental interaction of each block is altered at each transition.Fluorescence measurements using pyrene and 2-anilinonaphtalene showed that these dyes are incorporated in PdEA-core micelles formed above the LCST.Micellization temperatures can be controlled by adding additives such as salts and alcohols.Dependencies of micellization temperature on solvent composition is varied with properties of each block.For example, the UCST of PdMIN4AEAPS block decreases with increasing concentration of NaCI, but the UCST of poly(4-dimethyl(acrylaminopropyl) ammonium propane sulfonate)block increases.