SYNTHESIS AND MECHANICAL BEHAVIOR OF ISOTACTIC POLY(PROPYLENE OXIDE): A HIGH-STRENGTH, PHOTODEGRADABLE POLYMER

Abstract

For over 70 years, researchers have been optimizing conditions to produce isotactic polyethers from the ring opening polymerization of racemic epoxides. Although polyethers are produced on the commercial scale, most if not all of these polyethers are atactic. The original discovery of isotactic poly(propylene oxide) (iPPO), the simplest isotactic polyether, predates that of isotactic polypropylene. Its challenging synthesis from racemic propylene oxide has hindered mass development of this polymer. Until recently, catalysts for the polymerization of racemic epoxides produced mixtures of amorphous and semicrystalline materials. It wasn’t until 2005 that Coates et. al. developed the first catalyst able to produce near perfectly isotactic iPPO. This original Co-Salen catalyst pioneered the stereoselective and enantioselective polymerization of epoxides for the following 15 years. Today, researchers still work to develop isotactic polyethers, inspired by this original work by Coates. Despite 70 years of development, the mechanical properties of isotactic polyethers have remained unknown. Recent catalyst development allowed for the moderate scale production of highly isotactic, high molecular weight iPPO. We tookadvantage of the improved synthesis to thoroughly investigate the strength and degradation properties of this material (Chapter 2). The development of a tethered bimetallic catalyst led to the first production of narrowly disperse iPPO. Despite improved control over polymer dispersity and molecular weight, this catalyst was subject to an apparent induction period. Through a robust mechanistic study and catalyst modification, the induction period was essential removed (Chapter 3). Further improvements where made to this catalyst through systematic ligand variation (Catalyst 4). The improved synthesis and understanding of mechanical properties in iPPO provides an exciting framework for the future of this polymer.