TRANSIENT AND MECHANICAL PROPERTIES OF POLY(PHTHALALDEHYDE) AND THE VARIABLE FREQUENCY MICROWAVE CURING OF HIGH-PERFORMANCE THERMOSETS
Warner, Matthew J.
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Research presented in this thesis is split into two parts. The first section involves tuning the transient and mechanical properties of poly(phthaldehyde) to form a flexible, liquefiable transient material that can depolymerize upon the flick of a metaphorical switch. Such materials can be useful for devices designed to vanish into their surroundings once used. This application-based research required further understanding of how plasticizer additives work to not only make flexible films in an efficient manner, but how they can also serve to decrease the freezing point of o-phthalaldehyde, poly(phthaldehyde)’s monomer unit, upon degradation such that said devices can effectively disappear. Chapter 1 section 1.1 introduces how poly(phthalaldehyde) works as a transient material, and Chapter 1 section 1.2 describes some important fundamental concepts pertaining to how plasticizers can efficiently provide flexibility to polymers and how they work to reduce poly(phthaldehyde)’s freezing point upon depolymerization. Chapter 2 describes an initial approach used to successfully make flexible poly(phthaldehyde) films, and Chapter 3 describes an improved approach utilizing fundamental principles discussed in Chapter 1 section 1.2. Lastly, challenges regarding flexible poly(phthaldehyde)’s low strength are discussed. The second section involves studying the variable frequency microwave curing of epoxy and cyanate ester resins. Such resins are used for a broad range of applications, including microelectronic packaging, circuit board substrates, lightweighting, high- temperature performance parts, etc. Regardless of the application some thermosets, particularly those that possess a high glass transition temperature, require elevated temperatures above 100°C and cure times above 2 hours for complete cure. Variable frequency microwave heating as an alternative to conventional, thermal heating has been proposed as a method for reducing cure times and temperatures. However, proposed and sometimes conflicting microwave heating phenomena described by scientists and engineers are still not very well understood. Thus, the overarching goal of this section is to better understand and use microwave-heating mechanisms that can be useful in reducing thermoset cure times. This involves using a microwave field’s ability selectively heat reactive species (i.e. a catalyst) at the microscopic level, which can occur when two different materials of dissimilar dielectric parameters are mixed. Chapter 4 briefly summarizes important fundamentals of matter-interactions with microwave electromagnetic fields, and how it pertains to selective heating phenomena. Chapter 5 and 6 describe the microwave curing of high glass transition temperature, homogeneous epoxy and cyanate esters respectively. Chapter 7 describes microwave enhanced curing of cyanate ester resin upon the addition of graphene and reduced graphene oxide, two microwave-absorbing, catalytic fillers. Finally, the problems regarding quantifying selective heating phenomena and dielectric property characterization are described.