Show simple item record

dc.contributor.authorChen, Mingtaoen_US
dc.date.accessioned2018-08-09T08:00:56Z
dc.date.available2018-08-09T08:00:56Z
dc.date.issued2018-08-08
dc.identifier.othervt_gsexam:16669en_US
dc.identifier.urihttp://hdl.handle.net/10919/84525
dc.description.abstractAnionic polymerization and controlled radical polymerization enabled the synthesis of novel block copolymers with non-covalent interactions (electrostatic interaction and/or hydrogen bonding) to examine the relationships between mesoscale phenomenon and macroscopic physical properties. Non-covalent interactions offer extra intra- and inter-molecular interactions to achieve stimuli-responsive materials in various applications, such as artificial muscles, thermoplastic elastomers, and reversible biomacromolecule binding. The relationship between non-covalent interaction promoted mesoscale phenomenon (such as morphology) and consequent macroscopic physical properties is the key to optimize material design and improve end-use performance for emerging applications. Pendant hydrogen bonding in ABA block copolymers promoted microphase separation and delayed the order-disorder transition, resulting in tunable morphologies (through composition changes) and extended rubbery plateaus. Reversible addition-fragmentation chain transfer (RAFT) polymerization afforded a facile synthesis of ABA triblock copolymers with hydrogen bonding (urea sites) and electrostatic interactions (pyridinium groups). Pyridine groups facilitated hydrogen bonding through a preorganization effect, leading to highly ordered, long-range lamellar morphology and a significant increase of flow temperature (Tf) 80 °C above the hard block Tg. After quaternization of pyridine groups, electrostatic interaction, as a second physical crosslinking mechanism, disrupted ordered lamellar morphology and decreased Tf. Yet, extra physical crosslinking from electrostatic interactions pertained ordered hydrogen bonding at high temperature and exhibited improved stress-relaxation properties. Both conventional free radical polymerization and RAFT polymerization generated a library of poly(ionic liquid) (PIL) homopolymers with imidazolium groups as bond charge moieties. A long chain alkyl spacer between imidazolium groups and the polymer backbones ensured a low glass transition temperature (Tg), which is beneficial to ion conductivity. Four different counter anions enabled readily tunable Tgs all below room temperature and showed promising ion conductivities as high as 2.45 × 10⁻⁵ S/cm at 30 °C. For the first time, the influence of counter anions on radical polymerization kinetics was observed and investigated thoroughly using in situ FTIR, NMR diffusometry, and simulation. Monomer diffusion and aggregation barely contributed to the kinetic differences, and the Marcus theory was applied to explain the polymerization kinetic differences which showed promising simulation results. RAFT polymerization readily prepared AB diblock, ABA triblock and (AB)3 3-arm diblock copolymers using the ionic liquid (IL) monomers discussed above and deuterated/hydrogenated styrene. We demonstrated the first example of in situ morphology studies during an actuation process, and counter anions with varied electrostatic interactions showed different mesoscale mechanisms, which accounted for macroscopic actuation. The long chain alkyl spacer between imidazolium groups and polymer backbones decoupled ion dynamics and structural relaxation. For the first time, composition changes of block copolymers achieved tunable viscoelastic properties without altering ion conductivity, which provided an ideal example for actuation materials, solid electrolytes, and ion exchange membranes.en_US
dc.format.mediumETDen_US
dc.publisherVirginia Techen_US
dc.rightsThis item is protected by copyright and/or related rights. Some uses of this item may be deemed fair and permitted by law even without permission from the rights holder(s), or the rights holder(s) may have licensed the work for use under certain conditions. For other uses you need to obtain permission from the rights holder(s).en_US
dc.subjectpoly(ionic liquid)sen_US
dc.subjectelectrostatic interactionsen_US
dc.subjectblock copolymersen_US
dc.subjecthydrogen bondingen_US
dc.subjectRAFT polymerizationen_US
dc.subjectanionic polymerizationen_US
dc.titleBridging Mesoscale Phenomena and Macroscopic Properties in Block Copolymers Containing Ionic Interactions and Hydrogen Bondingen_US
dc.typeDissertationen_US
dc.contributor.departmentChemistryen_US
dc.description.degreePh. D.en_US
thesis.degree.namePh. D.en_US
thesis.degree.leveldoctoralen_US
thesis.degree.grantorVirginia Polytechnic Institute and State Universityen_US
thesis.degree.disciplineChemistryen_US
dc.contributor.committeechairLong, Timothy E.en_US
dc.contributor.committeememberSchulz, Michaelen_US
dc.contributor.committeememberMoore, Robert Bowenen_US
dc.contributor.committeememberCheng, Shengfengen_US


Files in this item

Thumbnail
Thumbnail

This item appears in the following Collection(s)

Show simple item record