Date of Award

2018

Document Type

Open Access Dissertation

Department

Chemistry and Biochemistry

Sub-Department

College of Arts and Sciences

First Advisor

Brian C. Benicewicz

Abstract

This dissertation focuses on the design, synthesis, characterization and application of matrix free polymer nanocomposites. Reversible addition-fragmentation chain transfer (RAFT) polymerization was used to synthesize block copolymers and polymer grafted silica nanoparticles with precise control over architectures.

In the first chapter, thermoplastic elastomer (TPE) grafted nanoparticles were prepared by grafting block copolymer poly(styrene-block-(n-butyl acrylate)) onto silica nanoparticles (NPs) (~15nm) via surface initiated RAFT polymerization. The effects of polymer chain length and graft density on the mechanical properties were investigated using films made solely from the grafted NPs. The ultimate tensile stress and elastic modulus increased with the increase of PS chain length. The dispersion of silica NPs and the microphase separation of block copolymers in the matrix-free polymer nanocomposite were investigated using small angle X-ray scattering (SAXS), transmission electron microscopy (TEM), differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). The higher polymer graft density TPEs exhibited better microphase separation of block copolymers and more uniform silica NP dispersion than lower polymer graft density TPEs with similar polymer chain length and compositions.

In the following chapter, we investigated the application of matrix-free polymer nanocomposites in the gas separation area. Polymer membranes have wide applications in gas separation. Poly(methyl acrylate) (PMA) and poly(methyl methacrylate) (PMMA) grafted silica NPs were synthesized by surface initiated RAFT polymerization. A versatile protocol was developed to remove ungrafted PMA from PMA grafted silica NPs from RAFT polymerization, which was implemented in place of a traditional ultracentrifuge procedure. The membranes from neat polymer grafted silica NPs exhibited an enhanced gas permeability over neat polymers, which was related to the increased free volume. The permeability can also be tuned by the grafted polymer molecular weight, which showed a “volcano plot” in permeability versus molecular weight. There was no aging effect on the membranes from polymer grafted NPs in the experimental measurement time line, which is important for practical applications in designing stable gas separation membranes.

Finally, the synthesis and applications of matrix free polymer grafted silica nanoplatelets as photonic crystals were investigated. One-dimensional photonic crystals can be formed by self-assembly of block copolymers, which typically need large molecular weight polymers. A new strategy for two different photonic crystals was constructed with different solvent responses and reflecting colors from the films of a single block copolymer. Initially, films made from poly(3-(triethoxysilyl)propyl methacrylate)-block-poly(stearyl methacrylate) with moderate molecular weight (PTEPM666-b-PSMA553 film) were responsive to alcohol with an observed stop band change from 365 nm (dry film) to 458 nm (film in ethanol), displaying a blue color. After conversion of the PTEPM domain to form SiO2 nanoplatelets, the PSMA553-g-SiO2 nanoplatelet film showed a larger stop band change from 365 nm (dry film) to 591 nm (film in THF), which reflected a bright orange color.

Available for download on Thursday, August 15, 2019

Included in

Chemistry Commons

Share

COinS