Synthesis and Applications of Depolymerizable, Phthalaldehyde-Based Polymers

The field of depolymerizable polymers is rapidly expanding as scientists and engineers discover new materials and applications for their use. The ability of a polymer to revert back to its intrinsic monomers with minimal activation energy and without the need for solvents is highly attractive from a chemical recycling perspective. Polymers with these attributes have also found critical roles for niche applications in semiconductor manufacturing and so-called “transient technology”, where materials and devices must be able to degrade and vanish into their local environment after its pre-determined lifetime. Polyaldehydes are one class of materials that have the ability to depolymerize from solid state polymers in response to certain stimuli. The vast majority of polyaldehydes are only metastable at ambient temperatures, and breaking a covalent bond along the backbone of the polymer initiates spontaneous depolymerization because the monomer state possesses a lower thermodynamic energy. Although polyaldehydes were thoroughly studied in the 1970’s and 1980’s, their instability at ambient conditions prevented commercialization, and interest in the materials waned. The past decade has seen a resurgence in the study of polyaldehydes, largely with applications focused on their ability to depolymerize under mild conditions. In particular, poly(phthalaldehyde) has been extensively studied in both fundamental and applied investigations. The overarching goals of the research presented in this dissertation is to better understand the thermodynamics and mechanisms governing o-phthalaldehyde polymerizations so that advanced materials can be better designed for engineering applications. The first two projects described herein explore synthesis of materials. First, a microflow reactor is used to investigate the kinetics and polymer chain growth mechanism of cationically polymerized poly(phthalaldehyde) to determine the rate limiting step in creating large polymers. The second explores fundamental thermodynamics for the copolymerization of o-phthalaldehyde with aliphatic aldehydes that can help change the physical and chemical functionalities of the resulting polymers. The last three studies described focus on semiconductor manufacturing applications using these materials. First, polyaldehydes are used as dry-develop resists for optical lithography to print micron-sized features and delineates various development processes. These polymers are then investigated to their use as sacrificial barrier materials that can be removed via thermolysis to leave behind pristine substrates. Finally, the synthesis of silicon-containing polyaldehydes are described and characterized as to their use as a resist for thermal scanning probe lithography with improved resistance to oxygen-based plasma etching.

Date

2020-11-24

Resource Type

Text

Resource Subtype

Dissertation

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