480579 Molecular Weight Distributions in Five Monomer Series

Monday, November 14, 2016
Grand Ballroom B (Hilton San Francisco Union Square)
Katherine Giles, Chemical and Biochemical Engineering, University of Iowa, Iowa City, IA, Nicole Kloepfer, University of Iowa and Julie L. P. Jessop, Chemical and Biochemical Engineering, The University of Iowa, Iowa City, IA

Changes in a polymer’s physical and mechanical properties can greatly impact performance. For example, small changes in the molecular weight distribution can drastically affect polymer strength and shrinkage. Understanding how processing conditions and monomer chemistry influence molecular weight distribution is critical to producing polymers with desired properties. These polymers can then be used as end-products with known behavior in industrial applications such as coatings, adhesives, and fibers. In this study, a series of five commercially available acrylate monomers were cured using ultraviolet light to initiate free-radical polymerization. The light intensity and exposure time were varied in order to determine how dose and dose rate influence the molecular weight distribution of each polymer. The chain growth and branching demonstrated in free radical polymerization varies according to the dose rate. After the samples were cured under ultraviolet light, they were dissolved in the solvent tetrahydrofuran (THF). The linear polymer chains (sol) were able to dissolve in the solvent and the highly cross-linked chains (gel) were filtered out using gravity filtration. Sol-gel is the ratio of the gel fraction to the sol fraction. The linear portion was then used to determine the sample’s molecular weight. To do so, gel permeation chromatography (GPC) was used to determine both the number average and weight average molecular weight. GPC separates polymers by size; smaller polymers move slowly through the column while larger particles have a shorter residence time. This size separation allows for the determination of molecular weight distribution. Preliminary data suggests dose and dose rate influence molecular weight distribution, but at this time only single trials have been performed for each of the five monomers. To confirm this trend, future work will focus on calculating sol-gel and determining molecular weight distribution for the five monomer series in triplicate. Additionally, this process could be extended to monomers outside the five monomer series to determine if other polymers follow the same trends.

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