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Title:Controlling the end groups and rates of catalytic polymerization
Author(s):Hyatt, Michael George
Director of Research:Guironnet, Damien S
Doctoral Committee Chair(s):Rauchfuss, Thomas B
Doctoral Committee Member(s):Fout, Alison R; Mirica, Liviu M
Department / Program:Chemistry
Degree Granting Institution:University of Illinois at Urbana-Champaign
chain transfer
Abstract:Functionalizing polymer end groups, telechelic polymers, can be synthesized through multiple methods including chain transfer polymerization. Chain transfer polymerization involves a catalyst that is capable of polymerizing a monomer, reacting with a chain transfer agent to cleave the polymer chain from the catalyst, and reinitiate the growth of a new polymer chain. However, the current catalysts and chain transfer agents used for the chain transfer polymerization of polyethylene are oxophillic, which severely limit the types of functional groups that can be introduced by the chain transfer agent, or require post polymerization reactions to achieve the desired functional group. This work aims to develop a chain transfer polymerization system capable of installing a wider range of functional groups into polyethylene by using a late transition metal catalyst as these are more stable towards the heteroatoms present in a functional chain transfer agent. The catalysts investigated in this work are a palladium phenanthroline catalyst for the production of polyketone from styrene and carbon monoxide, a palladium diimine catalyst for the production of hyperbranched polyethylene and a cobalt cyclopentadienyl catalyst for the production of high density polyethylene. These systems were chosen because of their ability to perform living polymerization as well as hydrosilylation. Hydrosilylation involves the cleavage of a metal carbon bond by a silane and subsequent insertion of olefin into the resulting metal-silicon bond, both key steps in a chain transfer polymerization system. The palladium phenanthroline catalyst is shown to be capable of forming silane end modified polyketone using HSi(ipr)3, however, the system is sensitive to water and requires 2,6-ditertbutylpyridine to inhibit formation of polystyrene. The key palladium-silyl intermediate is also highly unstable towards the comonomer carbon monoxide, causing major catalyst decomposition. The palladium diimine catalyst is shown to be capable of forming silane end modified hyperbranched polyethylene. Additionally the system can copolymerize methyl acrylate, while still retaining the desired silicon end groups. The cobalt cyclopentadienyl catalyst is shown to be able to form silane end modified high density polyethylene. The kinetics of the individual steps in this system were investigated, additionally a dye modified silane was successfully incorporated as an end group, demonstrating the stability of the chain transfer polymerization system towards heteroatoms. A second class of catalytic polymerization investigated is Ring Opening Metathesis Polymerization (ROMP) which is a widely used technique for the synthesis of polymers with controlled topology and composition. For ROMP catalyzed by the 3rd generation Grubb’s catalyst, an unusual zero order kinetic behavior in catalyst was observed, while it is first order in catalyst in the presence of additional pyridine. This unique kinetic behavior is rationalized by the catalyst having two coordinated pyridines in the solid state, while having only one coordinated pyridine in solution. Further investigations into the 3rd generation Grubb’s catalyst were performed by measuring the 12C/13C and 1H/2H kinetic isotope effect for the polymerization of a norbornene type monomer, which shows that the rate determining step is formation of the metallacyclobutane ring. Additionally, the effect of the side groups present on the monomer were investigated. Monomers containing esters can coordinate to the catalyst through the ester once polymerized, which slows down the rate of polymerization. This is shown for ester containing monomers that can form six membered rings, but not for eight membered rings. This polymer ester coordination is shown to be partly responsible for the rate differences between different stereochemistries (endo and exo) of the same monomer.
Issue Date:2020-07-01
Rights Information:Copyright 2020 Michael Hyatt
Date Available in IDEALS:2020-10-07
Date Deposited:2020-08

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