| 초록 |
This study concerns the micellization of PS-b-P2VP-b-PS triblock and PS-b-P2VP diblock copolymers in solvents that preferentially dissolve the middle block. In case of triblock, spherical micelles in these systems would consist of a core containing PS blocks, surrounded by loops of P2VP blocks. In fact, the absence of micelles in these systems has been reported by a number of workers. Previous theoretical work indicates that the entropic penalty associated with the looping of the coronal block is substantial and precludes the possibility of micelle formation in these systems. Dynamic and static light scattering measurements on solutions of polystyrene-b-poly(2-vinyl pyridine)-b-polystyrene triblock copolymer in ethanol and acetone mixed solvents, which is a selective solvent for the poly(2-vinyl pyridine) block, indicate that these systems can form micelles. In this work, we synthesized triblock copolymer by coupling PS-b-P2VP diblock copolymer using dichloro-p-xylene as the coupling agent, then we separated triblock and diblock copolymers perfectly by using HPLC method. The weight average molecular weights of triblock and diblock were 76 kg/mol (28k-20k-28k), 38 kg/mol (28k-10k), respectively. In the DLS measurement, the hydrodynamic radius of diblock copolymer micelle is larger than one of triblock copolymer as large as 16.4 nm. We identified that triblock copolymer formed micelle well in this system, but the size is smaller than diblock copolymer micelle because of loop-shaped structure of triblock copolymer. This result demonstrate that the previous theoretical analysis had overestimated the entropy of loop formation of the coronal block, and that micelle formation in this system is indeed possible. |
