The Transition Metal Catalyzed Polymerization of Heteroallenes: Cholesteric Gels and Cyclopolymerizations

From microscopic to macroscopic scale, the helix is a distinctive structure which can be found in nature. Synthetically prepared helices impart a wide variety of applications such as chiral separations, chiral sensing materials, optical materials, liquid crystalline materials, drug application and asymmetric catalysis to mention but a few. Improved materials for these applications by development of novel helical frameworks can unlock doors to a wide expansion in the real world. Chapter 1 briefly discusses the synthetic helical polymers, more specifically polycarbodiimides and polyisocyanates with their monomer synthesis, polymerization methods developed over the years and their controlled chiral polymer backbone formations along with their applications. Chapter 2 explains how the chirality in an achiral polymer can be induced using copolymerization. In other words, how single-handed chiral segments of static helical polymers of carbodiimides can be used to convert a racemic mixture of dynamic helical polymers of polyisocyanates into adapting a chiral polymer backbone. Copolymers of isocyanates and carbodiimides using CpTiCl2OCH2CF3 as the catalyst have been synthesized. Effective random copolymerization can be observed in the resulting polymers which has improved the chirality and handedness of the otherwise achiral poly(hexylisocyanate). Chapter 3 focuses on inducing chirality of the achiral racemic mixture of polyisocyanates using light cross-linking to lock in their helical reversals along the polymer backbone. The liquid crystalline mesophases of these crosslinked polymers have been improved from nematic mesophases to cholesteric mesophases. Chapter 4 discusses the synthesis and characterization of unique polymers of 1,2-dicarbodiimides that possess a cyclic structure throughout the polymer backbone by tethering the two functional groups close enough to promote their intramolecular reaction during the polymerization. New cyclo-polycarbodiimide polymers have been synthesized and display significant differences when compared to their acyclic counterparts.