Browsing by Author "Holmberg, Angela L."
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Item Bottom-up designs and syntheses of sustainable block polymers(University of Delaware, 2016) Holmberg, Angela L.In response to global environmental concerns, an immediate need for practical, eco-friendly, and non-hazardous plastics has irrupted, yet such materials are challenging to invent. Various sustainability issues associated with commodity plastics are addressed in this dissertation via bottom-up design strategies. The main targets are block polymers (BPs), architecturally unique macromolecules that are widely employed in thermoplastic elastomers (TPEs), pressure-sensitive adhesives (PSA), and coatings. For potential TPE and PSA applications, a library of monomers is developed using model components of inexpensive, abundant, non-food (lignin and waste vegetable oil) biomasses. The corresponding polymers have properties comparable to polystyrene (PS), a common petroleum-based plastic, so these new macromolecules could become sustainable alternatives to PS. An innovative strategy for polymerizing chemically distinct biobased monomers together also is investigated as a means for tuning and enhancing material properties at reduced costs. The approach involves the a priori prediction of kinetic parameters and polymer properties based on feedstock composition and monomer structure. For coatings applications, sustainability challenges associated with polymeric surfaces that repel both water and oil are addressed. Novel triblock terpolymers are synthesized, and their surface properties are characterized to show the design strategy’s potential effectiveness toward an aim of minimizing unsustainable fluorine content while maintaining repellency. Altogether, the reported approaches and similar de novo design strategies have the potential to revolutionize material sustainability.Item RAFT polymerization and associated reactivity ratios of methacrylate-functionalized mixed bio-oil constituents(Royal Society of Chemsitry, 2015-04-22) Holmberg, Angela L.; Karavolias, Michael G.; Epps, Thomas H. III; Angela L. Holmberg, Michael G. Karavolias and Thomas H. Epps, III; Holmberg, Angela L.; Karavolias, Michael G.; Epps, Thomas H. IIIThis work features a new suite of correlations for estimating kinetic parameters from multicomponent reversible addition–fragmentation chain-transfer (RAFT) polymerizations and an improved methodology for determining reactivity ratios in the pursuit of cost-effective and renewable plastics prepared from moderately processed bio-oils. Select monomers representing possible derivatives of compounds found in renewable bio-oils, such as pyrolyzed Kraft lignin and vegetable oils, were polymerized to investigate the consequences of structural diversity on the kinetics of RAFT polymerization. To facilitate predictions of heteropolymer dispersities and molecular weights, apparent chain-transfer coefficients (Capptr's) and propagation rate constants (kappp's) from homopolymerizations were correlated to kinetic parameters associated with the polymerization of bio-oil mixtures. Capptr depended on the reactivity ratios of the bio-oil components and the composition of the bio-oil feed, whereas kappp was related to only the composition of the bio-oil feed. A modified approach for analyzing Mayo–Lewis plots resulted in more accurate reactivity ratios and with greater precision in comparison to conventional nonlinear fitting procedures and traditional linearization fitting methods, respectively. The measured compositional data readily mapped onto the predicted monomer distribution profiles in multicomponent polymers, confirming the validity of the improved method described herein to determine reactivity ratios. Altogether, this manuscript offers a strategy for improving the viability of biobased polymers, addressing two key factors: minimizing separations costs by polymerizing bio-oil mixtures and preventing batch-to-batch inconsistencies in polymer properties by applying a priori knowledge about the bio-oil constituents’ individual kinetic parameters.