Date of Award

Spring 2024

Project Type

Dissertation

Program or Major

Chemistry

Degree Name

Doctor of Philosophy

First Advisor

John G Tsavalas

Second Advisor

Erik Berda

Third Advisor

Aylin Aykanat

Abstract

Environmental regulations on volatile organic compounds implemented in the European Union have highlighted the strengths of waterborne coatings and adhesives. Emulsion polymerization is a heterophase reaction in which an aqueous medium suspends polymer particles. Polymer colloids have diverse applications ranging from paper coatings, cosmetics, food additives, and pressure-sensitive adhesives, just to name a few. With such a wide range of applications, each latex requires a unique set of mechanical and chemical properties. One method used to control various mechanical properties is crosslinking, in which an insoluble “gel” is produced. Previous research by the Tsavalas group has revealed that alterations to the monomer feeding profile can aid in understanding cross-linking mechanisms. While symmetric crosslinkers have been extensively studied, a significant number cross-linkers are asymmetric, often containing a terminal allyl moiety for late incorporation into the polymeric network. These asymmetric crosslinkers are often far less studied in the open literature. Allyl methacrylate (ALMA) is a common crosslinker in various industrial products, yet little is known about its crosslinking mechanism. Bulk polymerization studies have shown ALMA to be an effective crosslinker, albeit without the expected kinetic acceleration due to the Trommsdorff–Norrish effect. This is attributed to the production of stabilized midchain radicals by ALMA, leading to kinetic retardation. Surprisingly, ALMA showed no sensitivity to changes in the monomer feeding profile as expected based on previous work with ethylene glycol dimethacrylate. However, it demonstrated sensitivity to hydrogen abstraction, evidenced by the comparison of the reaction kinetics at 40˚C where chain transfer is unfavored vs 70˚C where chain transfer is more pronounced. Quantum calculations were employed to better understand persulfate and hydroxyl radical attacks on ALMA and n-butyl methacrylate, shedding light on its unique crosslinking mechanism, which has not been reported in the literature to the level of detail discussed in this dissertation. Terminal allyls offer not only crosslinking benefits but also a solution to the coating industry's challenge of surfactant migration. During the drying process, the local concentration of surfactant, such as sodium dodecyl sulfate, is known to change specifically as surfactant leaves the surface of the latex particle and migrates to the air-water interface during water evaporation. This migration causes coating defects and is especially problematic when it leads to film delamination and water uptake, which can lead to the corrosion of metal substrates. To mitigate this issue, surfmers—surfactants covalently incorporated into the polymer—have been investigated. A library of five biobased surfmers was prepared and tested to determine their critical micelle concentration and their ability to act as colloidal stabilizers. Two surfmers demonstrated crosslinking capabilities, leading to a higher gel fraction, indicating their incorporation into the growing polymer chains. All five surfmers effectively stabilized polymer colloids without significantly affecting reaction kinetics. Among these, only the succinic-based surfmer showed improved stability, which can be explained by the ability of the sulfate group to diffuse to the polymer-water interface.

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