Title

Preparation of Initiator-Core Microcapsules and Their Use in Frontal Polymerization

Date of Award

2005

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemistry and Biochemistry

First Advisor

John Pojman

Advisor Department

Chemistry and Biochemistry

Abstract

Free-radical frontal polymerization is a method of converting monomer into polymer via a localized reaction zone that propagates through the monomer system. A significant issue for applying frontal polymerization to real-world applications is the issue of pot life, i.e., how long can the initiator-monomer solution remain at room temperature before reacting homogeneously. We sought to address this issue by microencapsulating a free-radical initiator, cumene hydroperoxide (CHP), and dispersing the capsules throughout a mixture of monomer and silica gel. Because the initiator would be sequestered from the monomer, theoretically it could not initiate polymerization until the capsules burst open upon heating. An investigation into the effectiveness of different microencapsulation techniques for the encapsulation of CHP was conducted. Techniques such as in situ polymerization, complex coacervation, and interfacial polymerization were attempted with varying degrees of success, with interfacial polymerization of a polyurea shell proving the most successful. Capsules produced were analyzed for size, shape, composition, and thermal properties. The CHP-core capsules that were produced were tested in a variety of free-radical frontal polymerization systems. It was observed that the microcapsules could be used successfully in a number of systems, and comparisons were made with typical frontal polymerization systems. The effect of encapsulation of CHP on the pot life was tested in a variety of systems, and it was observed that systems containing microcapsules underwent a dramatic increase in pot life. Polymer samples that were produced from 1,6 hexanediol diacrylate (HDDA) systems with and without microcapsules were tested for modulus and toughness. It was observed that the use of CHP-microcapsules resulted in an increase in the modulus and toughness of polymer samples. It was also observed that in systems stored over time, the mechanical properties of the polymers produced suffer as the capsules slowly leak CHP.