(511d) Sulfonate Functional Nano-Porous Membranes Templated from Ordered Block Copolymers

Block copolymers are known to micro-phase separate into different ordered structures such as lamellae, spheres and cylinders. Such morphologies can be used to template nano-porous materials for membranes and catalyst supports by selective etching of one of the blocks[1]. Poly(styrene)-poly(lactide) diblock copolymers were synthesized using nitroxide mediated polymerization (NMP) and ring opening polymerization (ROP). NMP was done with a hydroxyl functional initiator to produce a hydroxyl terminated poly(styrene) which was subsequently used as a macro-initiator to perform ROP of lactide catalyzed by triethylaluminum. Molecular weight distributions were narrow (Mw/Mn < 1.3) and careful purification of the macroinitiator was necessary for effective ROP. Sulfonation of the poly(styrene) segment was then performed to introduce anionic sites which may be useful for separation processes. After alignment of the cylindrical morphology by reciprocating shear, the poly(lactide) segment was removed selectively. The NMP and ROP and selective styrene sulfonation was extended to poly(t-butyl styrene)-poly(styrene)-poly(lactide) triblocks to produce a coaxial cylindrical morphology consisting of poly(lactide) cylinders within a poly(styrene sulfonate) functional walls surrounded by a non-functional poly(t-butyl styrene) matrix.

[1] Zalusky, A. S.; Olayo-Valles, R.; Wolf, J. H.; Hillmyer, M. A. J. Am. Chem. Soc. 2002, 124, 12761.