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Author ORCID Identifier

https://orcid.org/0000-0001-9203-2779

AccessType

Open Access Dissertation

Document Type

dissertation

Degree Name

Doctor of Philosophy (PhD)

Degree Program

Polymer Science and Engineering

Year Degree Awarded

2019

Month Degree Awarded

May

First Advisor

Alan J. Lesser

Subject Categories

Polymer and Organic Materials | Polymer Chemistry | Polymer Science

Abstract

This dissertation presents work focused on producing materials in non-equilibrium states by taking advantage of novel processing techniques. First, epoxy-based resins which can undergo radically promoted, cationic, thermal, frontal polymerization are investigated for their potential use as adhesives. These resins are found to be capable of sustaining propagating polymerization fronts between several different substrate materials, resulting in high levels of adhesion in some cases. In addition, a similar frontal resin was developed that can undergo sequential gelation and frontal polymerization. The gels are formed by radically crosslinking acrylate monomers within the epoxy resin. These gels can then be manipulated, and subsequently frontally polymerized into cross-linked glassy materials. This resin system shows a high degree of stability at room temperature in both the liquid and gelled state. A model was developed to describe the temperature and propagation rate of the front. The resin was also used to produce gelled carbon fiber composites which can be crosslinked with global heating, or frontal polymerization, forming cured composites. Supercritical CO2 (scCO2) was investigated to produce double-network materials from polyamide 6 (PA6) substrates. The scCO2 was used, in combination with methanol, as a solvent to diffuse and polymerize styrene within the amorphous regions of PA6. These PA6/Polystyrene double-network materials are found to have significantly different mechanical and sintering properties compared to PA6. It was also found that the PA6 and Polystyrene are not just trapped via molecular entanglements, but are covalently bound, as demonstrated by changes in solubility of the double-network material with varying polystyrene content. Finally, the same scCO2 method was used to diffuse and polymerize mixtures of blocked isocyanate and hydroxy functional methacrylate monomers within PA6. This was performed in an attempt to create a blend with latent functionality that could crosslink under sintering conditions used in selective laser sintering (SLS). It was found that, while deblocking of the isocyanates is evident at temperatures below the melting temperature of the double-network materials, no crosslinking is evident. However, when the material was held above its melting temperature, an increase in modulus and temperature at failure suggest that some degree of crosslinking may have occurred.

DOI

https://doi.org/10.7275/14220932

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