Copolymers of hydrophilic N-vinylpyrrolidone and hydrophobic alkyl methacrylates

Abstract

Hydrophobic interactions are known to be operative in the intra- and intermolecular interactions of proteins and certain synthetic macromolecules, and have been the subject of many extensive investigations. In the present study, hydrophilic N-vinylpyrrolidone was copolymerized with various alkyl methacrylates such as hexyl, dodecyl and octadecyl methacrylates. In addition to these methacrylates, 2,3-bis(octadecanoyloxy)propyl methacrylate(BODOPMA) which possesses two long alkyl chains, was also prepared and studied in search for any specific effect. Two compounds, 1-anilinonaphthalene-8-sulfonic acid salt (ANS) and cholesterol were employed as the hydrophobic probes to study the hydrophobic characters of the copolymers. Among the copolymers studied, the copolymer of N-vinylpyrrolidone with dodecyl methacrylate exhibited the strongest hydrophobic interaction with ANS and cholesterol. It was interesting to observe that the copolymer with BODOPMA adsorbed unexpectedly small amount of ANS and cholesterol, even though the formation of strong hydrophobic cluster was noted. When methanol was used as the solvent, no notable difference in hydrophobic characters was observed for the different copolymers. Concluded from these experimental observations is that in the presently investigated system, the adjacent two alkyl chains in BODOPMA are so tightly aggregated that the effective surface available for the interaction with hydrophobic probes become rather decreased in comparison with the independently isolated other alkyl groups.