Assembly of poly[N-(2-hydroxypropyl)methacrylamide] having cholesteryl moiety as terminal groups

Poly[N-(2-hydroxypropyl)methacrylamide]s (PHPMAs) with one pendant cholesteryl moiety at the polymer end and two pendant cholesteryl moieties at both polymer ends as terminal groups (PHPMA-Chol and PHPMA-2Chol) were prepared by the radical polymerization of N-(2-hydroxypropyl)methacrylamide initiated with 4,4′-azobis-[(3-cholesteryl) 4-cyanopentanoate] in the presence of 2-mercaptoethanol and thiocholesterol as chain-transfer reagents, respectively. The self-organization of the PHPMAs was analyzed by fluorescence and 1H NMR measurements. The critical micelle concentration (CMC) decreases with a decreasing PHPMA degree of polymerization. The CMC of PHPMA-Chol is much larger than that of PHPMA-2Chol. PHPMA exhibits an excellent blood compatibility, as determined from the Michaelis constant for the enzymatic reaction of thrombin and a synthetic substrate, S-2238, in the presence of PHPMA-2Chol. According to a small-angle X-ray scattering measurement, PHPMA-2Chol can hold the cholesterol molecule as a lipophilic drug model in a hydrophobic layer formed by terminal-located cholesteryl groups in PHPMA-2Chol.