Advances in the Modeling of Synthesis, Design and Properties of Polymers

Abstract

Atomistic simulations can be an integral part of the development and exploration of polymers and provide useful insight to help guide experimental discovery. This dissertation in particular reveals computational insights into the synthesis and properties of emerging polymeric materials. In the smallest cases the utilization of quantum chemical methods provides insight into the chemical reactivities of catalyzed reactions. In the largest, the use of molecular mechanics predicts the macroscopic surface interactions between adhesives and contact surfaces.

At the level of chemical reactions existing computational methods can be sufficient to predict chemical pathways. Chapter 2 utilizes Density Functional Theory to describe the catalytic behavior of a living, enantioselective propylene oxide polymerization catalyst with an extended incubation period. The results of the analysis found that adventitious water, as hydroxide, through ring opening reaction with propylene oxide to form 1,2-hydroxypropanol, created a low energy trap state. Additionally, 1,2-hydroxypropanol can form from a chain transfer agent, 1,2-propandiol, which was correlated to extended incubation periods in experimentation. This understanding of the trap state led to rigorous drying conditions and alternative chain transfer agents, which eliminated the incubation period.

Chemical reactivities are not always well-described by existing computational methods. Chapter 3 develops and applies relativistic quantum mechanical methods to elucidate the mechanism of palladium aerobic oxidation. The catalyst analyzed was found to react slowly at room temperature and in the presence of air, key mechanistic steps were unable to be resolved experimentally due to their short lived nature. Additionally, the intersystem crossing of O2, facilitated by the catalyst, is expected to be strongly influenced by relativistic effects. Relativistic electronic structure studies resolved the key intermediates, transition states and minimum energy crossing points for the two literature suggested mechanisms. The barrier to reactivity was found to be O2 insertion into a Pd-H bond after which spin degeneracy and spin-orbit coupling allow for intersystem crossing. Moreover, the rate limiting step in the catalytic pathway was found to align with experimental observations of catalyst reactivity.

Expanding system size to the level of polymeric property prediction requires the application of molecular mechanics, rather than quantum chemical methods. In Chapters 4 and 5 molecular mechanics are used to predict the adhesive ability of adhesives, both existing and novel compositions, in aqueous environments. Chapter 4 targets adhesive selectivity in pure water environments towards common microplastic surfaces through manipulation of monomeric composition of polyacrylate adhesives. The result of this analysis is that thermodynamic selectivity can be achieved by reducing adhesive surface energy below the interfacial energy to a specific polymer, driving interfacial formation. Furthermore, physical principles leading to lowering surface energies are assessed to guide future investigations. Importantly, these computational results are compared against experimental analysis and found to agree with the predicted selectivities. Chapter 5 expands the scope of the aqueous environment to account for in situ contamination found in laundry effluents, a common site of microplastic generation. Through the construction of concentration response curves, estimates of adhesion at concentrations consistent with laundry effluents can be determined. It was found that even at the lower concentrations of effluents, contaminants can have a measurable impact on the strength of adhesives binding microplastics. Moreover, morphological changes, such as adsorption and fiber formation, due to contaminant interaction were found. These morphological modifications provide insight into the long-term environmental changes of both adhesives and microplastics.