Master of Sciences (Engineering), Case Western Reserve University, 2020, Macromolecular Science and Engineering

A novel approach to develop well-defined hyperbranched star polymers is presented herein. The unique three-dimensional structures were synthesized by an arm-first star polymerization route, coupled with an A2 + B3 approach that utilized the copper-catalyzed azide-alkyne cycloaddition (CuAAC). The synthesis of these new materials is relatively straight-forward, and the size of the resultant stars can be easily tuned by varying the reaction conditions. Because the synthesis is tolerant of various different functional groups, there is potential to achieve access to a large library of distinctive star polymers with differing chemical properties. In this vein, the method was used to create stars from polystyrene and polyacrylonitrile starting materials. Moving forward, the unique properties of the materials–highly soluble polymers with both peripheral functional groups and many interior "pockets" offering potential spaces for site isolation– can be used to gain a better understanding of polymer-supported catalysis. Furthermore, it is the hope that these materials are the next step in bridging the gap between the catalytic ability and functional breadth of enzymes as compared to synthetic catalysts.

Committee: Valentin Rodionov (Committee Chair) Subjects: Organic Chemistry; Polymer Chemistry

Doctor of Philosophy, University of Akron, 2011, Polymer Science

A variety of methods were used to make polymers with different architecture and functionalities. The linking chemistry of vinyldimethylchlorosilane (VDMCS) with poly(styryl)lithium (Mn = 1,700-3,000 g/mol) was studied. The average degree of branching varied from 7.5 to 9.4 with an increase in concentration of VDMCS (1.2 to 5.2 eq). The intrinsic viscosities and melt viscosities (at 160 °C) of the star polymers were found to be less than half of that of the corresponding linear polystyrenes. α-Pyrrolidine-functionalized polystyrene (Mn = 2,700 g/mol, Mw/Mn = 1.03, 92.5%) was successfully synthesized from α-chloromethyldimethylsilane-functionalized polystyrene(Mn = 2,600 g/mol, Mw/Mn = 1.02) based on NMR spectroscopy, MALDI-TOF and ESI mass spectrometry. The stability of silyl hydride groups under atom transfer radical polymerization conditions was proven by copolymerizing methyl methacrylate and (4-vinylphenyl)dimethylsilane (VPDS). Tapered block copolymers of isoprene, VPDS, and styrene with narrow molecular weight distributions (1.04 and 1.05) were synthesized via anionic polymerization. Evidence regarding the topology of cyclic polybutadienes was obtained by Atomic Force Microscopy of grafted polymers obtained by grafting an excess of silyl hydride functionalized polystyrene (Mn = 8,300 g/mol, Mw/Mn =1.01) onto cyclic polybutadiene(Mn=88,000 g/mol, Mw/Mn = 2.0). The reactivity of polyisobutylene carbocations was compared with respect to competitive electrophilic addition to a vinyl group versus silyl hydride transfer by investigating the reaction with VPDS. Based on GPC results, and 1H and 13C NMR spectroscopy, no evidence for any vinyl group addition was observed. A successful attempt was made to prepare electrospun fibers from fluorofunctionalized styrene-butadiene elastomers. The water contact angle of these surfaces was found to be 162.8o ± 3.8o for the fibrous mat of the fluorinated polymers as compared to 151.2o ± 2.4o for the analogous fibrous (open full item for complete abstract)

Committee: Roderic Quirk Dr. (Advisor); Mark Foster Dr. (Committee Chair); Judit Puskas Dr. (Committee Member); Chrys Wesdemiotis Dr. (Committee Member); Kevin Cavicchi Dr. (Committee Member) Subjects: Polymers

Doctor of Philosophy, University of Akron, 2007, Polymer Science

Novel methods for the synthesis of chain-end and in-chain functionalized polymers, as well as star polymers, were developed using anionic polymerization techniques. A new mechanism for the reaction of polymeric organolithium compounds with thiiranes has been found. The reaction of poly(styryl)lithium and poly(butadienyl)lithium with propylene sulfide and ethylene sulfide was investigated in hydrocarbon solution for the preparation of thiol-functional polymers. It was found by MALDI-TOF mass spectral analysis of the reaction products that the reaction proceeded by attack of the anion on the methylene carbon atom of the thiirane ring followed by ring opening to form the thiol-functionalized polymer. The reaction of poly(styryl)lithium with trimethylene sulfide did not produce the corresponding thiol-functionalized polymer; the resulting methyl-terminated polymer was formed by attack of the anion on the sulfur atom followed by ring opening to form a primary carbanion. A new method for synthesis of alkoxysilyl-functionalized polymers was developed. Using a general functionalization methodology based on the hydrosilation of vinyltrimethoxysilane with w-silyl hydride-functionalized polystyrene, alkoxysilyl-functionalized polystyrene was obtained in high yield (83 %). The main side product was vinylsilane-functionalized polymer. A small amount of dimer (approximately 2 %) was formed from the hydrosilation reaction of silyl hydride-functionalized polymer and vinylsilane-functionalized polymer. Star polymers with an average number of 6.8 arms were obtained by reacting poly(styryl)lithium with 6.6 equivalents of vinyldimethylchlorosilane in benzene at 30 C. It was found that, in benzene at 30 C, vinyldimethylchlorosilane is an efficient linking agent for the preparation of well-defined star-branched polymers. In contrast, the reaction of poly(styryl)lithium with 5 equivalents of vinyldimethylchlorosilane in THF at -78 C produced vinylsilane-functionalized polymer in high yiel (open full item for complete abstract)

Committee: Roderic Quirk (Advisor) Subjects: Chemistry, Polymer

Doctor of Philosophy, Miami University, 2022, Chemistry and Biochemistry

Polymers are everywhere and they are made up of a series of repeating units chained together. With increased demand for polymers with tailored applications, methods such as atom transfer radical polymerization (ATRP) and reversible addition-fragmentation chain transfer (RAFT) were created in order to gain control of the growing chains. These methods provide a way to synthesize chains with known molecular weights and low dispersity. This work was designed to explore polymerization methods at its core. The analysis of the reaction rates is based on retardation, reaction conditions, and chain transfer reagent composition in order to help better understand the RAFT reaction mechanism. Looking at quintessential RAFT, many assumptions have been made about every aspect of the reaction; from choosing a chain transfer reagent all the way to the solvent choice. Many of these preconceived notions have not been thoroughly tested in parallel to each other. Here, we analyzed reaction rate along with chain length and dispersity to see how the growing polymers responded to variations from the literature standard. Rate retardation is the decrease in reaction rate as the concentration of chain transfer reagent increases. In our study, we analyzed beyond traditional dithiobenzoate chain transfer reagents in order to understand the universality of rate retardation within RAFT. RAFT also allows for complex architecture with unique physical properties, such as star polymers, blocks, and gradients. Within this dissertation, these complex architectures are studied by looking at the unique physical properties as well as the kinetics and composition of the polymer. This was important when analyzing the folding of the ortho-phenylene core of a star polymer and understanding how R group affects the control of synthesizing gradient polymers by RAFT.

Committee: Dominik Konkolewicz (Advisor); C. Scott Hartley (Advisor); Suzanne Harper (Committee Member); Richard Page (Committee Member); David Tierney (Committee Chair) Subjects: Chemistry

PhD, University of Cincinnati, 0, Engineering and Applied Science: Materials Science

A recent method to quantify molecular topologies of various materials using small-angle scattering has been used to quantify fractal systems like polymer solutions and ramified aggregate structures. Small angle x-ray and neutron scattering has been used to characterize ceramic aggregates and polymer systems respectively. Ramified aggregates are formed in many dynamic processes such as in flames. Such structures are disordered and present a challenge to quantification. The topological quantification of such nanostructured materials is important to understand their growth processes. Small-angle X-ray scattering (SAXS) is widely used to characterize such nanoparticle aggregates. The details in ceramic aggregates like branch fraction, number of segments in an aggregate and the short circuit path, coordination number and the number of end groups are extracted. In order to explicitly determine the nature of chain scaling, related to topology or solvent quality, as well as to quantifying the thermodynamic interactions, the coupling of the unified scattering function with the Random Phase Approximation (RPA) equation and inter-arm interactions based on Benoit's approach is proposed to enable analytical quantification of these effects using a scaling model. The scattering function places structural constraints from the model to limit the Unified Fit Function for hierarchal scattering. A detailed topological quantification of star polymer systems has been able to describe both, good and theta solvent conditions along with effect of functionalities, as well as resolve deviations in chain conformations due to steric interactions between star arms. An investigation on different solvent conditions for 6-arm polyurethane star polymers was done and the scaling parameters were extrapolation to zero entropy collapsed and extended chain states to understand the possible topological variations in the system. Polyisoprene star polymers under good solvent condition were used (open full item for complete abstract)

Committee: Gregory Beaucage Ph.D. (Committee Chair); Jude Iroh Ph.D. (Committee Member); Vikram Kuppa Ph.D. (Committee Member); Vesselin Shanov Ph.D. (Committee Member) Subjects: Materials Science

Doctor of Philosophy, Case Western Reserve University, 1990, Chemistry

The objective of this research was to prepare star-block polymers which have potential surface activity. The basic method was ring-opening polymerization of 2-substituted oxazolines of differing polarities. In a preliminary phase, homo-, di- and tri- blocks were synthesized using a one-ended initiator. Triblocks were also prepared using several two-ended initiators, resulting in molecular weight distributions that were unacceptably broad. It was determined through a kinetic study that the reason for the broad distributions is that the initiation step is slower than the propagation step. The same problem was encountered when attempting to produce a three-armed star-block polymer starting with a trifunctional nosylate initiator. For this reason, it was decided to abandon the "core-first" approach and to proceed with an "arms-first" approach, in which one-ended living poly(N-benzoylethyleneimine) chains are reacted with an anchoring moiety containing one or two primary amine groups. First the poly(N-benzoylethyleneimine) polymers were synthesized, and their molecular weight distributions characterized by Gel Permeation Chromatography (GPC) and by Secondary Ion Mass Spectroscopy (TOF-SIMS). Using a monoarmine anchor, it was found that one or two chains could be attached at will, depending upon the ratio of arms to anchors. Using a diamine anchor with a four-to-one arm to anchor ratio, a star-block polymer mixture was obtained in which the desired four-armed star predominated. Confirming GPC data are presented, accompanied by TOF-SIMS and 1H NMR spectra.

Committee: Irvin Krieger (Advisor) Subjects: Chemistry, Polymer