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Author ORCID Identifier

https://orcid.org/0000-0003-2822-7998

AccessType

Open Access Dissertation

Document Type

dissertation

Degree Name

Doctor of Philosophy (PhD)

Degree Program

Polymer Science and Engineering

Year Degree Awarded

2022

Month Degree Awarded

February

First Advisor

Thomas J. McCarthy

Second Advisor

E. Bryan Coughlin

Third Advisor

Sarah L. Perry

Subject Categories

Polymer and Organic Materials | Polymer Science

Abstract

This dissertation presents research performed in the field of silicone polymer science, which refers to polymers with alternating silicon-oxygen backbones. Three research topics will be explored. The first topic involves the synthesis of trimethylsiloxysilsesquioxane (MT) copolymers with vinyl and hydride functionalities as reactive liquid silicone precursors. The second topic describes titration of dimethylsiloxy (D) composition into trimethylsiloxysilsesquioxane (MT) copolymers for the purpose of controlling the mechanical properties and thermal stabilities of the material. The last topic explores the modification of hydrophobic silicone surfaces with oxygen plasma to form silica-like, hydrophilic surfaces and the behaviors of hydrophobic recovery.

The first chapter provides a general review of silicone polymers with an emphasis on the simplicity of the chemistry and rational science that underpins the experiments that were carried out in this thesis research. The history of silicone polymers is introduced, as well as the key chemistry reactions that are utilized in the thesis research: (1) hydrolysis and condensation of methoxysilanes, and (2) hydrosilylation of olefins and hydridosilanes. Finally, some basic concepts of surface wetting including contact angles and contact angle hysteresis are presented.

Three separate, but interrelated projects are presented after this introduction. In the first project described in Chapter 2, trimethylsiloxy-terminated phenylsilsesquioxane (MTϕ) copolymers were prepared using modifications of procedures used to prepare (homo)poly(phenylsilsesquioxane) (pTϕ), the structures of which are discussed in detail. With the addition of trimethylsiloxy monomers with vinyl (MV) or hydride (MH) functionalities, MTϕ copolymers were obtained as precursors with control over silanol content and M to T ratio. These reactive MTϕ copolymers were crosslinked by hydrosilylation between vinyl and hydride, and hard silicone materials were formed with excellent thermal stabilities.

In the second project described in Chapter 3, the mechanical properties of crosslinked silicones were controlled by titrating dimethylsiloxy (D) composition into trimethylsiloxymethylsilsesquioxane (MT) silicones. The intrinsic rigidity of the crosslinked MT network results in a high modulus of the material. By bringing the flexibility of D composition into the network, the moduli of the crosslinked materials are able to be controlled. D composition was titrated during the preparation of reactive liquid precursors, and was controlled by D:T feed ratio, which could predict the moduli of final crosslinked materials. The structure-property relationships were also explored in terms of this network structures.

The last project described in Chapter 4, entails research involving the hydrophobic recovery of silicone surfaces. Oxygen plasma was utilized to generate hydrophilic surfaces with silica reactivity on some of the crosslinked silicones discussed in the first and second projects. The hydrophobic recovery process was monitored by dynamic contact angle using water as a probe fluid. The MT networks exhibited slower recovery compared with common PDMS networks.

DOI

https://doi.org/10.7275/26833919

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