Synthesis of various classes of chiral polymers and their application in enantioselective separation.

Abstract

Doctoral thesis work aims to develop chiral polymeric chiral selectors and a cost-effective enantioselective filtration method. Polyfluorene having protected D/L-aspartic acid pendants groups were synthesized by Suzuki polymerization. Synthesized polyfluorene with chiral pendants were coated on anodic aluminium oxide (AAO) membranes. These chiral polyfluorene coated AAO were utilized to separate the racemic mixture of 9 different native amino acid by a simple filtration method. Where highest separation of ~95 % enantiomeric excess (ee) was achieved in case of glutamic acid. Further effect of different chiral pendants groups on selectivity and separation efficiency was determined by synthesizing polyfluorenes with protected L-Tryptophan and L-glutamic acid as pendant. These polymers were coated on porous AAO membranes and these polymer coated membranes were used to achieve enantioselective separation of 10 different amino acid racemic mixtures. L-glutamic acid containing membranes achieve highest separation of glutamic acid (~92 % ee) while L-tryptophan containing polymer show highest separation in case of tryptophan (~91 % ee) and phenylalanine (~88 % ee). Thus separation efficiency and highly depend upon the nature of pendant group and type of interaction involve. Though π-conjugated polymer coated AAO membranes achieve better separation, but overall cost hindered its scalability. Thus commodity polymers (polystyrene) was synthesized by solvent free RAFT polymerization followed by its post polymer modification with L-leucine derivative by single step Friedel-Craft acylation. The microspheres of the chiral polystyrenes were used to achieve enantioselective separation of the leucine and alanine racemic mixture. The low separation values compare to conjugated. We tried to address this issue by synthesizing chiral π-conjugated polymers by a relatively greener direct heteroarylation (DHAP) polymerization method. Overall, the work provides a simple, cost-effective, and efficient enantioselective filtration method using chiral polymeric membranes or microspheres as a chiral selector.