Doctoral Dissertations

Date of Award

5-2018

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Chemistry

Major Professor

Jimmy W. Mays

Committee Members

Mark Dadmun, Charles S. Feigerle, Kevin M. Kit

Abstract

Thermoplastic elastomers with thermally reversible physical crosslinks are ideal alternates to thermoset rubbers because of their recyclable and reprocessible nature. Styrenic block copolymers represent the most inexpensive block copolymers on the market. However, challenges remain in tailoring thermal and mechanical properties and enhancing upper service temperature.Living anionic polymerization (LAP) is the most powerful synthetic technique to generate well-defined polymers and block copolymers. In this dissertation, we present preparation of new functionalized macromonomers and block copolymers by LAP. Our aim is to develop TPEs with enhanced UST and tailorable properties by design of macromonomers with tunable conformation and functionalizable TPEs with ability in undergoing versatile post-polymerization modification.General aspects of styrenic TPEs, motivations, classic and state-of-the-art linear ABA triblock copolymer TPEs, followed the importance of macromonomers in preparing multigraft copolymer TPEs with exceptional elasticity are presented, in Chapter 1. High vacuum experimental techniques in LAP are also introduced.Incorporating PBF into multigraft copolymer side chains enables the thermal and mechanical properties of multigraft TPEs to be tuned by changing architecture and conformation. We describe the first synthesis of polybenzofulvene (PBF) macromonomer with styrenic end-functional groups through four different approaches by LAP and post-polymerization modification. The pros and cons of each method are discussed accordingly.In the next chapter, we discuss the correlation of microstructure, chain flexibility and glass transition temperature of PBF by studying the solution properties (specifically, characteristic ratio C∞). PBF with varied 1,2-/1,4 addition ratios were prepared by LAP. Their intrinsic viscosity and molecular weights were readily measured for monodisperse fractions by online SEC equipped with multiple detectors. The Burchard-Stockmayer-Fixman (BSF) model was used to derive C∞.The preparation and characterization of a highly functionalizable ABA block copolymer TPE with poly(4-vinyl pyridine) (P4VP) hard segments is discussed in Chapter 4. Morphological, mechanical properties and thermal properties were studied for diblock and triblock copolymers with different compositions and molecular weights.In the end, conclusions and prospects for future work are presented.

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