Abstracts Category : Other

I. Controlled Aqueous C1 Synthesis of Telechelic Macromonomers for the Synthesis of Long-Chain Aliphatic Polyesters. II. Evaluation of 9-Borafluorene Derivatives as the Catalysts for the Polyhomologation Reaction

by Ruobing Zhao

My dissertation includes five research projects on the polyhomologation reaction for synthesis of carbon backbone polymers. In chapter 1, an overview is provided on the polyhomologation reaction. The reaction builds linear sp3 carbon chains one carbon at a time using an organoborane catalyst. The traditional method is a living polymerization using sulfoxonium ylides under anhydrous conditions. The newly developed aqueous method is a polymerization of sulfoxonium salts in an aqueous base.Chapter 2 develops the synthesis of telechelic polymers including -hydroxyacid esters, ,-diols and ,-diacids using the aqueous polyhomologation reaction with control of chain length and PDI. These polymers were used as macromonomers to produce long-chain aliphatic polyesters. The obtained polyesters have thermal and mechanical properties indistinguishable compared to related materials derived from biomass.Chapter 3 reports the synthesis of a gradient ersatz ethylenepropylene copolymer using the traditional polyhomologation reaction. A new and convenient source of the ethylide monomer was developed for the introduction of methyl branch on the polymer backbone. The gradient copolymer contains a gradual change of methyl branch content along the polymer chain.Chapter 4 focuses on the precise monomer insertion on a carbon chain using a sulfonium benzylide. The polymerization and validation protocols were established to demonstrate the precise insertion. A thermally more stable benzylide needs to be developed to complete this study.In chapter 5, three 9-borafluorene derivatives are designed and evaluated in search of a single-site catalyst for the polyhomologation reaction. The catalyst is being developed for the synthesis of the yet unknown polyethylidene. Computational studies indicated a preferred 1,2-migration of the sp3 over sp2 carbon when an electron-withdrawing group is installed on the aromatic rings at the ortho position to boron. Experimental studies revealed the presence of competing sp2 carbon migration due to the required high reaction temperature from the high activation energy of 1,2-migration. A side reaction produced ethylidenemethylidene copolymers rather than polyethylidene due to the competing decomposition of ethylide.In chapter 6, an air-stable borane initiator was provided for convenient use in the polyhomologation reaction. Polymer molecular weight and polydispersity are well controlled using the amineborane complex.