Interpenetrating polymer networks (IPNs) of polystyrene-polybutadiene-polystyrene (SBS) block copolymers and polystyrene (PS) were prepared using sequential network formation with the polybutadiene (PB) of the SBS crosslinked thermally and the styrene network formed thermally or by ??-radiation. The use of ??-radiation to cure the added PS network at room temperature successfully avoided thermal degradation of the butadiene segments within the SBS which had been observed in earlier studies. Both linear SBS and radial SB4 IPNs were studied to compare the influence of linear or branched block copolymers on the IPN morphology. The molecular morphology was examined using a suite of techniques including thermal analysis (DSC and DMA), transmission electron microscopy (TEM), atomic force microscopy (AFM) and smallangle X-ray and neutron scattering (SAXS and SANS). The primary SBS/SB4 network morphology was found to dominate the IPN morphology with the secondary styrene network limited to selectively swelling the PS domains. The linear SBS IPNs displayed a more ordered morphology than the radial SB4 IPNs, and this morphology was investigated in pseudo three-dimensions by sectioning samples in two perpendicular directions. The morphology was found to be consistent with thermally formed systems prepared in previous studies, and contained styrenic domains of 20-50 nm within a continuous butadiene matrix. The weight of evidence suggested that the lamella structure dominated the linear SBS IPNs and a cylindrical structure for the radial SB4 IPNs. Maximum values of tensile strength and elongation at break (20 MPa and 140% respectively) were observed in samples with a styrene cure ??-radiation dose of 200 kGy. The SANS analysis of these polymer systems was expanded to investigate the thermal formation of the added PS network in real time. Time-resolved SANS allowed the development of nanostructures in the bulk samples to be measured, and compared to previous time-independent TEM studies on thin sections. The formation of the styrene network was most noticeably observed in a linear SBS IPN system, in which an increase in long-range order was observed and attributed to movement of styrene monomer into the styrenic domains and sharpening of the phase boundaries between the PS and the PB regions.

Dissertation (Ph.D.)--Auburn University, / Abstract. Includes bibliographic references (p.187-189).

Thesis advisor: Dunwei Wang / As an inedible component of biomass, lignin features rich functional groups that are desired for chemical syntheses. How to effectively depolymerize lignin without compromising the more valuable cellulose and hemicellulose has been a significant challenge. Existing biomass processing procedures either induce extensive condensation in lignin that greatly hinders its chemical utilization or focus on fully depolymerizing lignin to produce monomers that are difficult to separate for subsequent chemical synthesis. Here, we report a new approach to selective partial depolymerization, which produces oligomers that can be readily converted to chemically recyclable polymer networks. The process takes advantage of the high selectivity of photocatalytic activation of the β-O-4 bond in lignin by decatungstate catalysts (DT). In the photocatalytic system, DT works as both catalyst and oxidant, leading to two different reaction pathways, slow and steady bond cleavage pathway, and fast but limited oxidation pathway. The availability of exogenous electron mediators or external oxidants promotes cleavage or oxidation of this bond, respectively, enabling high degrees of control over the depolymerization and the stoichiometry of a key functional group, C═O, in the products. The resulting oligomers can then be readily utilized for the synthesis of polymer networks through reactions between C═O and branched −NH2 as a dynamic covalent cross-linker. Importantly, the resulting polymer network can be recycled to enable a circular economy of materials directly derived from biomass. / Thesis (PhD) — Boston College, 2024. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Chemistry.

Thesis (M. S.)--Materials Science and Engineering, Georgia Institute of Technology, 2008. / Committee Chair: Kenneth Gall; Committee Member: David Bucknall; Committee Member: Karl Jacob.

Thesis (Ph. D.)--Drexel University, 2005. / Includes abstract and vita. Includes bibliographical references (leaf 221).

Thesis (Ph. D.)--Drexel University, 2005. / Includes abstract and vita. Includes bibliographical references.

Microwave processing of polymeric adhesives and composites offers great potential for future materials development. However, basic considerations need to be established which will allow the processing of polymeric systems, both as reactive thermosetting systems and as nonreactive thermoplastics. Fundamental studies relating epoxy network generation to processing conditions have been investigated in a tunable, single-mode microwave cavity at a frequency of 2.45 GHz. These studies demonstrate that in as little as ten minutes fully cured networks with good mechanical properties can be generated. Furthermore, toughened epoxy systems which utilize carefully designed amine-terminated poly (arylene ether sulfone) thermoplastics as reactive oligomers have novel phase-separated morphologies. In fact, it has been demonstrated that the morphology in these multiphase systems may actually be controlled by utilizing microwave processing. In addition to epoxy resins, the microwave processing of functionalized poly(arylene ether ketone)s (PEK) has also been demonstrated. PEK's are typically classified as high performance thermoplastics; however, with the appropriate terminal functionalities these ductile thermoplastics may also be transformed into tough, solvent resistant networks. In the current investigation amine-, maleimide- and nadimide-terminated PEK's of controlled molecular weights were synthesized and crosslinked by both electromagnetic radiation (EMR) processing and classical thermal treatments. EMR processing resulted in network formation at rates as high as 20 times faster than conventional thermal treatments at the same isothermal cure temperature. Relationships among processing conditions, curing rates and endgroup functionality were investigated. Novel poly (arylene ether ketone)/poly(aryl imide) homo- and poly (dimethylsiloxane) segmented copolymer blend systems have been investigated to determine the influence of chemical structure on miscibility and physical property behavior. Melt processing results demonstrate that the glass transition temperature of PEEK™ blends increase monotonically with polyimide content. Indeed, T_g'S as high as 240°C have been achieved for certain blend compositions, while still retaining adequate crystallization to provide solvent resistance. The experimental T_g results are in good agreement with the theoretical values predicted by the Fox equation. Lastly, electromagnetic processing was applied to PEEK™/Ultem™ blends to demonstrate the principles of "microwave calorimetry". / Ph. D.

Several novel characterization techniques were developed to gain a molecular-level understanding of the effects of exposure intensity and exposure time on photopolymer network formation. These techniques enable detailed characterization of photopolymer behavior in real-time and post-exposure. In situ dynamic mechanical analysis was performed to observe the changes in composite modulus during photopolymerization of thin acrylate films supported on stainless steel grid sheets. Vitrification phase transformations were monitored in real-time via remote sensing dielectric spectroscopy. The relationship between exposure intensity and vitrification time revealed the exposure conditions necessary to shift the crosslinking rate from reaction kinetics controlled to diffusion kinetics controlled. The effect of exposure intensity and exposure time on chemical conversion was ascertained via Fourier transform infrared microspectroscopy mapping experiments. The relationship between exposure intensity and time at a given conversion level revealed an increased occurrence of radical isolation at higher conversions. Furthermore, the exposure necessary to maintain a fixed conversion indicated greater reciprocity failure at lower conversions, indicative of classical radical termination kinetics. / Ph. D.

Thesis (MSc)--Stellenbosch University, 2003. / ENGLISH ABSTRACT: In this thesis the formation and properties of a polymer gel on and at a surface are investigated. The gel under investigation is defined as a three-dimensional network of macromolecules that form permanent links with one another and also with confining planar surfaces. The precise location of the crosslinks on the wall or on another macromolecule is not known prior to linking, and will differ from sample to sample. However, once the crosslinks are formed, they are assumed to be permanent. This random linking is the source of the disorder in the system, over which a quenched average has to be taken. An existing model [9] of network formation, with polymer-polymer crosslinks, is extended to incorporate a surface and polymersurface crosslinks. Within the framework of replica theory, statistical averages and physical properties of the system are calculated by means of a variational approach. Macroscopic information, in terms of the free energy of deformation, is obtained by using two different potentials to simulate the erosslinks mathematically. / AFRIKAANSE OPSOMMING: In hierdie tesis word die vorming en eienskappe van 'n polimeergel, wat teen 'n oppervlak gevorm word, ondersoek. Die gel word gedefinieer as 'n drie-dimensionele netwerk van makromolekules wat permanente bindings met mekaar, maar ook met twee inperkende, platvlakke, vorm. Die presiese ligging van die bindings op die muur en op ander makromolekules is nie vooraf bekend nie, en sal verskil van een gel-monster tot die volgende. Sodra die konneksies egter gevorm is, word aanvaar dat hulle permanent is. Die lukrake bindingsproses is die oorsprong van wanorde in die sisteem, waaroor 'n wanorde-gemiddelde bereken moet word. 'n Bestaande model [9]van netwerkvorming, met polimeer-polimeer bindings, word uitgebrei om 'n oppervlakte en polimeer-oppervlak bindings in te sluit. Statistiese fisika gemiddeldes en fisiese eienskappe van die sisteem word binne die raamwerk van replika-teorie en 'n variasie benadering bereken. Makroskopiese inligting, in terme van die vrye energie van vervorming, word verkry deur twee verskillende potensiale te gebruik om die konneksies wiskundig voor te stel.

published_or_final_version / abstract / Dentistry / Doctoral / Doctor of Philosophy