Soluble polymer-supported catalysts and initiators
The development of polymer-supported chiral organic ligands for transition metal asymmetric catalysis is an area of research that is continuously receiving a lot of interest. This methodology addresses the major issue of recyclability and waste/product stream contamination in conventional homogeneous catalysis. The use of soluble polymers, as supports, couples the advantages of homogeneous and heterogeneous catalysis and offers a means of recycling often expensive chiral ligands. The goal is to recycle the catalysts over multiple runs without loss of its activity. A novel semi-continuous technique for recycling soluble polymer-supported catalysts—“Soxhlet-Dialysis”—has been developed whereby the catalyst's activity and enantioselectivity is maintained over multiple runs. It was also observed that the spacer that linked the polymer to the catalyst had an unprecedented effect on the activity and enantioselectivity of the catalyst. Electronic effects on enantioselectivity of chiral Zn-salen catalysts were studied, and logical interpretation of the results provided the basis for a postulated catalytic mechanism. “Living” Free Radical Polymerization using a soluble polymer supported initiator was employed for the design of well-defined cleavable PS-b-PEG diblock copolymers for the fabrication of nanoporous thin films.