Tailoring polymer synthesis with designer ruthenium catalysts

Abstract

The research presented in this thesis focuses on applying ring-opening metathesis polymerization (ROMP) toward the synthesis of advanced macromolecular architectures. Chapter 1 provides an overview of the olefin metathesis reaction and evaluates the various synthetic tools currently employed for preparing complex polymeric structures. Chapters 2 and 3 summarize the performance of various Ru-based catalysts in ROMP. Chapter 2 focuses on complexes coordinated with various N-heterocyclic carbene ligands while Chapter 3 focuses on their phosphine ligated analogs and methods to improve their initiation efficiency. The scope and utility of these catalysts in various ROMP reactions are discussed. Chapters 4 and 5 describe the synthesis of acetoxy, hydroxy, and vinyl end-functionalized polybutadienes (PBDs) and polynorbornenes. By including allyl acetate, 1,4-bis(acetoxy)-2-butene, or 2-butene-1,4-diol as chain transfer agents (CTAs) during a Ru mediated ROMP of cyclooctadiene (COD) or norbornene (NBE), the respective end-functionalized polymers with molecular weights controllable up to 30 kDa could be obtained in high yield. Chapter 6 describes a one-pot synthesis of triblock copolymers composed of mechanistically incompatible segments. Bis(allyl chloride) and bis(2-bromopropionate) end-functionalized telechelic PBDs were synthesized by the ROMP of COD in the presence of the corresponding difunctional CTAs. These telechelic PBDs were subsequently used as difunctional macroinitiators for the atom transfer radical polymerization (ATRP) of styrene or methyl methacrylate (MMA) to form the respective block copolymers. Chapter 7 describes the synthesis of a multifunctional Ru complex which was found to be capable of mediated both the ROMP of COD and the ATRP of MMA to form diblock copolymers. Depending on the reaction conditions, the complex was found to catalyze both polymerizations either in tandem or simultaneously. Introduction of hydrogen at the conclusion of the polymerizations resulted in quantitative saturation of the polymer backbone. Chapters 8 and 9 describe a new synthetic route to cyclic polymers. In this approach, the ends of growing polymer chains remain attached to a cyclic Ru catalyst throughout the entire polymerization process. This effectively excludes all types of linear intermediates, which were a major drawback of previous approaches to cyclic polymers. Techniques for characterizing and determining the purity of cyclic polymers are also discussed.