AMPHIPHILIC POLY(N-ISOPROPYLACRYLAMIDES) PREPARED BY USING A LIPOPHILIC RADICAL INITIATOR - SYNTHESIS AND SOLUTION PROPERTIES IN WATER

Amphiphilic poly(N-isopropylacrylamides) (PNIPAM) substituted with two pendant n-octadecyl groups at the chain end were prepared by free-radical polymerization in dioxane of N-isopropylacrylamide (NIPAM) using 4,4'-azobis(4-cyano-N,N-dioctadecyl)pentanamide (DODA-501) as the initiator. Copolymers differing in the molar ratio of octadecyl groups to N-isopropylacrylamide units were obtained by varying the initiator to monomer ratio. Their composition was established by H-1 NMR spectroscopy. The solution properties of the polymers were studied as a function of polymer concentration and temperature. Quasi-elastic light scattering measurements and fluorescence experiments with two probes, pyrene and bis-(1-pyrenylmethyl) ether (dipyme), reveal the existence of multimolecular micelles below the lower critical solution temperature (LCST) in solutions of concentration exceeding ca. 0.1 g L-1. The micelles consist of a rigid core of octadecyl chains and a corona of solvated PNIPAM chains. These collapse at the LCST. The collapsed micelles aggregate, resulting in macroscopic phase separation of the solutions.