Title

Reactivity of Vegetable Oil Macromonomers in Thiol-ene, Cationic, and Emulsion Polymerizations

Date of Award

2007

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Polymers and High Performance Materials

First Advisor

James W. Rawlins

Advisor Department

Polymers and High Performance Materials

Abstract

Vegetable oils were, and continue, to be a mainstay in unsaturated polyester ("alkyd") technology. Our endeavor is to use vegetable oil-based polymers in environmentally-friendly coatings. The role of vegetable oil cis -unsaturation has not been fully explored in polymers. To that end, vegetable oil macromonomers (VOMMs) in three different systems were investigated to determine the involvement of cis -unsaturation in chain transfer, auto-oxidation, and copolymerization reactions. VOMMs were incorporated into UV curable thiol-ene coatings, UV cationic coatings, and acrylic solution copolymers and fundamental studies were conducted to determine how and to what extent cis -unsaturation contributes to film performance properties. In thiol-ene UV curable coatings, cis -unsaturation was involved in the initial curing reaction and to lesser degrees, in postcure crosslinking. Its behavior was determined to be dependent on the ene component. Thiol-ene photopolymerization yielded homogeneous networks but formulations containing VOMMs exhibited greater heterogeneity due to non-uniformity in the VOMM chemical structures, and the concurrent reactions occurring during thiol-ene photopolymerization and "dark cure". Partially epoxidized soybean oil was synthesized to contain varying levels of residual cis -unsaturation. Cationic photopolymerization of partially epoxidized soybean oil yielded lightly crosslinked films, but the influence of free radical decomposition byproducts has not been fully investigated. The low involvement of the cis -unsaturation in photopolymerization was attributed to its low reactivity and/or radical combination with antioxidants and molecular oxygen dissolved in the films. When used in emulsion polymerization, VOMMs lower the minimum filming temperature during coalescence and increase the Tg after application via auto-oxidation. Free radical polymerization of VOMMs is accompanied by chain transfer reactions between polymer radicals and VOMMs that reduces molecular weight and the auto-oxidation potential of the film. Retardation in polymerization rate correlated directly with increase in amount of unsaturation and conjugated unsaturation. Vegetable oils containing significant amounts of fatty acids with bisallylic hydrogen atoms were found to be more reactive towards chain transfer than fatty acids containing monoallylic hydrogen atoms. Model polymers were produced by functionalizing methacrylic copolymers through a mild reaction pathway in the absence of radicals. Copolymers with large quantities of bisallylic hydrogen atoms showed increased auto-oxidation reactivity as evidenced by greater consumption of cis -unsaturation and higher gel fractions.