STAR AND CYLINDRICAL MICELLES OF POLYSTYRENE-BLOCK-POLY(2-CINNAMOYLETHYL METHACRYLATE) IN CYCLOPENTANE

Polystyrene-block-poly(2-cinnamoylethyl methacrylate) (PS-b-PCEMA) sam ples with n/m larger than 9.0, where n and m stand for the numbers of styrene and of CEMA units in a chain, formed essentially star micelles and those with n/m between 7 and 8.2 formed mixtures of star and long cylindrical micelles in cyclopentane with PCEMA as the core and PS as the shell. UV cross-linking of the PCEMA cores of these micelles at 5 0 degrees C yielded star polymers and nanofibers. This probably repres ents the first preparation of cross-linked block copolymer cylindrical micelles or nanofibers in the solution phase. While we have previousl y prepared star polymers using this approach, this study shows the rob ustness of this method in producing star polymers with as many as 4.5 x 10(2) arms and a molar mass of 9.9 x 10(7) g/mol. Detailed study sho wed that UV cross-linking only lacked in the structure of the micelles and did not change their aggregation numbers. This allowed us to dete rmine the molar masses of the cross-linked micelles in toluene, in whi ch uncross-linked micelles would have disintegrated, and to equate the m to those of the uncross-linked micelles in cyclopentane. The aggrega tion numbers of the star micelles in cyclopentane were found to follow theoretical scaling laws.