Assembly of Poly[N-(2-hydroxypropyl)methacrylamide] Having Long Alkyl Moieties as Terminal Groups
Kazuo SUGIYAMA* and Ryo HANAMURA
Program in Material Technology, Graduate School of Industrial Technology, Kinki University; 1 Umenobe, Takaya, Higashihiroshima-shi 739-2116 Japan
Amphiphilic poly[N-(2-hydroxypropyl)methacrylamide]s (PHPMA) having long alkyl moieties as terminal groups, PHPMA-C12, PHPMA-DC12 and PHPMA-C18, were prepared by radical polymerization of N-(2-hydroxypropyl) methacrylamide (HPMA) initiated with lipophilic azo-initiators such as 4,4'-azobis(dodecyl 4-cyanopentanoate) (VA-C12), 4,4'-azobis[(2-dodecyloxy-1-dodecyloxymethylethyl) 4-cyanopentanoate] (VA-DC12) and 4,4'-azobis(octadecyl 4-cyanopentanoate) (VA-C18) in the presence of 2-mercaptoethanol as a chain transfer reagent. An amphiphilic polymer having octadecyl moieties as both terminal groups, PHPMA-2C18, was also prepared by radical polymerization of HPMA initiated with VA-C18 in the presence of 1-octadecanethiol (ODT) as a chain transfer reagent. From the fluorescence measurements of aqueous polymer solution using 1-(6-dimethylamino-2-naphthyl)-1-dodecanone (DMAND) as a fluorescent probe, the critical micelle concentrations (CMC) of PHPMAs were found to be PHPMA-C12PHPMA-DC12>PHPMA-C18PHPMA-2C18 in order. From SAX measurements of a drug model consisting of PHPMA-C18 and cholesterol, it was suggested that cholesterol molecules are incorporated in a hydrophobic domain formed by the terminal octadecyl groups. It was also found that no acceleration in the enzymatic reaction of thrombin and a synthetic substrate S-2238 occurred in the presence of PHPMA-C12, PHPMA-C18, or PHPMA-2C18. These PHPMAs are thus expected as carrier molecules of drug delivery system.
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