Date of Award

5-2015

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Chemistry

Major Professor

Bin Zhao

Committee Members

Jimmy Mays, Michael Best, Shanfeng Wang

Abstract

Mixed homopolymer brushes, composed of two distinct homopolymers randomly or alternatively immobilized by one end on a solid substrate, exhibit intriguing phase behavior. This dissertation work focuses on synthesis and morphology study of well-defined mixed brushes grafted on 150 – 180 nm silica particles. The brushes were grown from asymmetric difunctional initiator (Y-initiator)-functionalized silica particles by using two “living”/controlled polymerization techniques.

Chapter 1 is an introduction to mixed brushes. Chapter 2 presents a study on the effect of overall grafting density (soverall) [Sigma overall] on morphology of mixed poly(tert-butyl acrylate) (PtBA)/polystyrene brushes synthesized by sequential surface-initiated atom transfer radical polymerization of tBA and nitroxide-mediated radical polymerization (NMRP) of styrene from Y-initiator-functionalized particles. By changing the mass ratio of Y-initiator to silica particles in the initiator immobilization step, a series of brush samples with different soverall values but similar molecular weights (MW) were synthesized. Transmission electron microscopy showed that at soverall ³ 0.34 chains/nm2 [chains/nanometer square], the brushes formed “rippled” structures after cast from chloroform. The normalized ripple wavelength (D) scaled with soverall-0.47 [sigma overall to the -0.47 power] in the soverall range of 1.06 to 0.54 chains/nm2.

Chapter 3 describes a study on the effect of MW on morphology of mixed PtBA/PS brushes on silica particles. A series of samples with different average MWs, from 13.8 to 33.1 kDa, but comparable soverall were made and their morphologies were investigated. For samples cast from chloroform, D scaled with MW0.70 [MW to the 0.7 power] in the studied MW range. For uniformly collapsed mixed brushes cast from water, D was proportional to MW0.56 [MW to the 0.56 power].

Chapter 4 presents the synthesis of mixed brushes from Y-initiator-functionalized silica particles by surface-initiated ring-opening polymerization and NMRP. The soverall of mixed brushes can be tuned by varying the mass ratio of Y-initiator to silica particles in the initiator immobilization step. Chapter 5 describes the synthesis of two polymer brush acid catalysts and their applications for fructose dehydration to 5-hydroxymethylfurfural in water. Both brush catalysts exhibited a higher catalytic activity than the corresponding free polymer catalysts. Chapter 6 presents conclusions and future work.

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