Light scattering study of poly(tert-butyl methacrylate) -block-poly(1,1-dihydroperfluorooctyl methacrylate) in liquid and supercritical carbon dioxide - Towards the reversible control of self-assembly

Self-assembly of CO2-soluble amphiphilic diblock copolymers consisting of p oly(tert-butyl methacrylate) (P'BMA) and poly(1,1-dihydroperfluorooctyl met hacrylate) (PFOMA) was studied in liquid and supercritical carbon dioxide. Dynamic light scattering studies demonstrated that the diblock copolymers, having a P'BMA length greater than 4000, self-assembled into micelles with narrow molecular weight distributions. The copolymers having hydrodynamic r adii of micelles between 13 and 21 nm exhibited a transition from micelles to unimers in the CO2 density range of 0.87 similar to1.04 g/cm(3). The exa ct transition density was dependent upon temperature and upon the length of the two polymer chains composing the diblock. This is the first light scat tering study demonstrating that the micelles-to-unimers transition of block copolymers in CO2 is controlled through variation of the block length of t he diblock copolymers. This suggests that it is possible to control the sel f-assembly of block copolymers not only by manipulating the solvent quality of the CO2 medium, but also by choice of the block length of the diblock c opolymer.