Title

Design, Synthesis, and Characterization of Vegetable Oil Macromonomers in Auto-Oxidative Crosslinking Latexes

Date of Award

2005

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Polymers and High Performance Materials

First Advisor

Shelby F. Thames

Advisor Department

Polymers and High Performance Materials

Abstract

This research focuses on designing and synthesizing vegetable oil macromonomers to evaluate their auto-oxidative crosslink capabilities in latex polymers. Unsaturated fatty acids are extensively employed in various types of polymers due to their ability to improve chemical and mechanical properties via crosslinking. This chemistry has not been fully exploited in environmentally friendly emulsion polymers partly due to the colloidal and polymeric characteristics of latexes that imparts numerous technical challenges. Several methodologies have been applied to synthesize these hybrid polymers, and the Thames Research Group has focused on copolymerizing acrylate-modified vegetable oil adducts, i.e., vegetable oil macromonomers, with slightly water-soluble monomers that are routinely employed in latex polymerizations. The copolymerization behavior of saturated, lipophilic macromonomers with the conventional monomers was used to model their behavior in an aqueous environment. The results indicated that hydrophobic macromonomers do not efficiently copolymerize with the slightly water-soluble monomers using the macroemulsion technique. A nonuniform distribution of crosslinker between polymer particles has adverse effects on the film's ability to form interparticle crosslinks. Efforts to improve the degree of copolymerization between the lipophilic macromonomers and conventional monomers were unsuccessful using the macroemulsion technique. Unfortunately, the minimemulsion technique has limitations that reduce its industrial utility because this process can enhance the reaction between the model and conventional monomers. In light of these findings, the research focus was shifted to developing VOMMs with enhanced hydrophilicity to improve the copolymer's chemical distribution uniformity. An optimal VOMM was designed with ethylene oxide moieties to increase hydrophilicity via hydrogen bonding. The timing and composition of the monomer feed(s) in macroemulsion polymerizations primarily controls the resulting particle morphology. Ethoxylated vegetable oil-based macromonomers were synthesized and introduced into the polymerization during a second-stage monomer feed, promoting interparticle networking from increased crosslinker concentration near the particle's periphery. This method was employed to synthesize latex polymers, and these films were evaluated for their ability to improve performance properties. After curing at ambient conditions, these films displayed significant increases in solvent resistance, and this property was found to increase as a function cure schedule and cobalt drier concentration, indicating an auto-oxidative mechanism was active. Complementary NMR analysis also revealed the polymer chain's mobility was reduced after curing from network formation.