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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

d-Limonene, a Renewable Component for Polymer Synthesis

Ren, Shanshan January 2017 (has links)
d-Limonene (Lim) was used in various polymer formulations to achieve a more sustainable polymerization. Lim is a renewable and essentially non-toxic compound, derived from citrus fruit peels, that may replace some of the many toxic and fossil-based chemicals used in polymer synthesis. Bulk free-radical polymerizations of n-butyl acrylate (BA) with Lim were performed to investigate Lim co-polymerization kinetics and estimate the monomer reactivity ratios, important parameters in the prediction of copolymer composition. Kinetic modeling of the BA/Lim copolymerization was performed with PREDICI simulation software. The model supports the presence of a significant degradative chain transfer reaction due to Lim. This reaction mechanism is due to the presence of allylic hydrogen in Lim. Nonetheless, relatively high molecular weight polymers were produced. It was concluded that Lim behaves more like a chain transfer agent than a co-monomer. Terpolymerizations of BA, butyl methacrylate (BMA) with Lim were then performed. In order to predict the terpolymer composition, the monomer reactivity ratios for BA/BMA were estimated. By applying the three pairs of co-monomer reactivity ratios to the integrated Mayo-Lewis equation, terpolymer compositions were ably predicted up to high monomer conversion levels. Lim was then used as a chain transfer agent to prepare core-shell latex-based pressure sensitive adhesives (PSA) comprising BA and styrene via seeded semi-batch emulsion polymerization. By varying the concentration of Lim and divinylbenzene crosslinker, the core polymer microstructure was modified to yield different molecular weights and degrees of crosslinking. The core latex was then used as a seed to prepare core-shell latexes. By changing the Lim concentration during the shell-stage polymerization, the molecular weight of shell polymer was also modified. The latexes were characterized for their microstructure and were cast as films for PSA performance evaluation. The PSA performance was shown to be highly related to the polymer microstructure. Tack and peel strength showed a decrease with increasing Lim concentration. Shear strength went through a maximum with a core Lim concentration increase from 0 to 5 phm.
2

Evaluation of instantaneous and cumulative models for reactivity ratio estimation with multiresponse scenarios

Zhou, Xiaoqin January 2004 (has links)
Estimating reactivity ratios in multicomponent polymerizations is becoming increasingly important. At the same time, using cumulative models is becoming imperative, as some multicomponent systems are inherently so fast that instantaneous "approximate" models can not be used. In the first part of the thesis, triad fractions (sequence length characteristics) are employed in a multiresponse scenario, investigating different error structures and levels. A comparison is given between instantaneous triad fraction models and instantaneous composition model, which represent the current state-of-the-art. In the second part of the thesis, extensions are discussed with cumulative composition and triad fraction models over the whole conversion range, thus relating the problem of reactivity ratio estimation to the optimal design of experiments (i. e. optimal sampling) over polymerization time and conversion. The performance of cumulative multiresponse models is superior to that of their instantaneous counterparts, which can be explained from an information content point of view. As a side-project, the existence of azeotropic points is investigated in terpolymer (Alfrey-Goldfinger equation) and tetrapolymer (Walling-Briggs equation) systems.
3

Evaluation of instantaneous and cumulative models for reactivity ratio estimation with multiresponse scenarios

Zhou, Xiaoqin January 2004 (has links)
Estimating reactivity ratios in multicomponent polymerizations is becoming increasingly important. At the same time, using cumulative models is becoming imperative, as some multicomponent systems are inherently so fast that instantaneous "approximate" models can not be used. In the first part of the thesis, triad fractions (sequence length characteristics) are employed in a multiresponse scenario, investigating different error structures and levels. A comparison is given between instantaneous triad fraction models and instantaneous composition model, which represent the current state-of-the-art. In the second part of the thesis, extensions are discussed with cumulative composition and triad fraction models over the whole conversion range, thus relating the problem of reactivity ratio estimation to the optimal design of experiments (i. e. optimal sampling) over polymerization time and conversion. The performance of cumulative multiresponse models is superior to that of their instantaneous counterparts, which can be explained from an information content point of view. As a side-project, the existence of azeotropic points is investigated in terpolymer (Alfrey-Goldfinger equation) and tetrapolymer (Walling-Briggs equation) systems.
4

Nonlinear Parameter Estimation for Multiple Site-Type Polyolefin Catalysts Using an Integrated Microstructure Deconvolution Methodology

Al-Saleh, Mohammad A. 16 March 2011 (has links)
The microstructure of polyolefins determines their macroscopic properties. Consequently, it is essential to predict how polymerization conditions will affect polyolefin microstructure. The most important microstructural distributions of ethylene/alfa-olefin copolymers made with coordination catalysts are their molecular weight (MWD), chemical composition (CCD), and comonomer sequence length (CSLD). Several mathematical models have been developed to predict these microstructural distributions; reliable techniques to estimate parameters for these models, however, are still poorly developed, especially for catalysts that have multiple site types, such as heterogeneous Ziegler-Natta complexes. Most commercial polyolefins are made with heterogeneous Ziegler-Natta catalysts, which make polyolefins with broad MWD, CCD, and CSLD. This behavior is attributed to the presence of several active site types, leading to a final product that can be seen as a blend of polymers made on the different catalyst site types. The main objective of this project is to develop a methodology to estimate the most important parameters needed to describe the microstructure of ethylene/alfa-olefin copolymers made with these multiple site-type catalysts. To accomplish this objective, we developed the Integrated Deconvolution Estimation Model (IDEM). IDEM estimates ethylene/alf-olefin reactivity ratios for each site type in two-steps. In the first step, the copolymer MWD, measured by high-temperature gel permeation chromatography, is deconvoluted into several Flory’s most probable distributions to determine the number of site types and the weight fractions of copolymer made on each of them. In the second estimation step, the model uses the MWD deconvolution information to fit the copolymer triad distributions measured by 13C NMR and estimate the reactivity ratios per site type. This is the first time that MWD and triad distribution information is integrated to estimate the reactivity ratio per site type of multiple site-type catalysts used to make ethylene/alfa-olefin copolymers. IDEM was applied to two sets of ethylene-co-1-butene copolymers made with a commercial Ziegler-Natta catalyst, covering a wide range of 1-butene fractions. In the first set of samples (EBH), hydrogen was used as a chain transfer agent, whereas it was absent in the second set (EB). Comparison of the reactivity ratio estimates for the sets of samples permitted the quantification of the hydrogen effect on the reactivity ratios of the different site types present in the Ziegler-Natta catalyst used in this thesis. Since 13C NMR it is an essential analytical step in IDEM, triad distributions for the EB and EBH copolymers were measured in two different laboratories (Department of Chemistry at the University of Waterloo, and Dow Chemical Research Center at Freeport, Texas). IDEM was applied to both set of triad measurements to find out the effect of interlaboratory 13C NMR analysis on reactivity ratio estimation.
5

Nonlinear Parameter Estimation for Multiple Site-Type Polyolefin Catalysts Using an Integrated Microstructure Deconvolution Methodology

Al-Saleh, Mohammad A. 16 March 2011 (has links)
The microstructure of polyolefins determines their macroscopic properties. Consequently, it is essential to predict how polymerization conditions will affect polyolefin microstructure. The most important microstructural distributions of ethylene/alfa-olefin copolymers made with coordination catalysts are their molecular weight (MWD), chemical composition (CCD), and comonomer sequence length (CSLD). Several mathematical models have been developed to predict these microstructural distributions; reliable techniques to estimate parameters for these models, however, are still poorly developed, especially for catalysts that have multiple site types, such as heterogeneous Ziegler-Natta complexes. Most commercial polyolefins are made with heterogeneous Ziegler-Natta catalysts, which make polyolefins with broad MWD, CCD, and CSLD. This behavior is attributed to the presence of several active site types, leading to a final product that can be seen as a blend of polymers made on the different catalyst site types. The main objective of this project is to develop a methodology to estimate the most important parameters needed to describe the microstructure of ethylene/alfa-olefin copolymers made with these multiple site-type catalysts. To accomplish this objective, we developed the Integrated Deconvolution Estimation Model (IDEM). IDEM estimates ethylene/alf-olefin reactivity ratios for each site type in two-steps. In the first step, the copolymer MWD, measured by high-temperature gel permeation chromatography, is deconvoluted into several Flory’s most probable distributions to determine the number of site types and the weight fractions of copolymer made on each of them. In the second estimation step, the model uses the MWD deconvolution information to fit the copolymer triad distributions measured by 13C NMR and estimate the reactivity ratios per site type. This is the first time that MWD and triad distribution information is integrated to estimate the reactivity ratio per site type of multiple site-type catalysts used to make ethylene/alfa-olefin copolymers. IDEM was applied to two sets of ethylene-co-1-butene copolymers made with a commercial Ziegler-Natta catalyst, covering a wide range of 1-butene fractions. In the first set of samples (EBH), hydrogen was used as a chain transfer agent, whereas it was absent in the second set (EB). Comparison of the reactivity ratio estimates for the sets of samples permitted the quantification of the hydrogen effect on the reactivity ratios of the different site types present in the Ziegler-Natta catalyst used in this thesis. Since 13C NMR it is an essential analytical step in IDEM, triad distributions for the EB and EBH copolymers were measured in two different laboratories (Department of Chemistry at the University of Waterloo, and Dow Chemical Research Center at Freeport, Texas). IDEM was applied to both set of triad measurements to find out the effect of interlaboratory 13C NMR analysis on reactivity ratio estimation.
6

REACTIVITY RATIO CONTROLLED POLYCONDENSATION AS A ROUTE TO SYNTHESIZE FUNCTIONAL POLY(ARYLENE ETHER)S

Boakye, Godfred January 2014 (has links)
No description available.
7

Investigations into the Propagation and Termination Kinetics of the Radical Polymerization of Polar Monomers in Aqueous Solution

Schrooten, Jens 24 October 2012 (has links)
Propagations- und Terminierungsgeschwindigkeitskoeffizienten radikalischer Polymerisationen in w&auml;ssriger L&ouml;sung wurden durch Pulslaser-induzierte Polymerisationen und durch chemisch initiierte Polymerisationen bestimmt. Pulslaser-induzierte Polymerisationen wurden von <i>N</i>,2&#8209;Dimethylprop&#8209;2&#8209;enamid, <i>N</i>,<i>N</i>&#8209;Dimethylprop&#8209;2&#8209;enamid, 2&#8209;Methylprop&#8209;2&#8209;enamid und Prop&#8209;2&#8209;enamid durchgef&uuml;hrt. Anschlie&szlig;ende Analyse der Produkte mittels Gr&ouml;&szlig;enausschlusschromatographie erm&ouml;glichte die Bestimmung der Propagationsgeschwindigkeitskoeffizienten. Die beobachtete &Auml;nderung des Propagationsgeschwindigkeitskoeffizienten mit der Monomerkonzentration kann durch die St&auml;rke, mit der innere Rotationen und Vibrationen im &Uuml;bergangszustand des Propagationsschritts gehindert sind, erkl&auml;rt werden. Die Abh&auml;ngigkeit der St&auml;rke der Hinderung von der Monomerkonzentration l&auml;sst sich zur&uuml;ckf&uuml;hren auf sich mit steigendem Monomeranteil verst&auml;rkende intermolekulare Wechselwirkungen der &Uuml;bergangszustandsstruktur mit solvatisierenden Molek&uuml;len. Zur Bestimmung der Aktivierungsvolumina und der Arrhenius-Aktivierungsenergien der Propagation wurden Druck und Temperatur von Umgebungsdruck bis 2&nbsp;000&nbsp;bar beziehungsweise von 10&nbsp;&deg;C bis 80&nbsp;&deg;C variiert. Sowohl die Aktivierungsenergie als auch der Betrag des Aktivierungsvolumens sind im Fall von 2&#8209;Methylprop&#8209;2&#8209;enamid gr&ouml;&szlig;er verglichen mit <i>N</i>,<i>N</i>&#8209;Dimethylprop&#8209;2&#8209;enamid. Diese Beobachtung kann dem Umstand, dass <i>N</i>,<i>N</i>&#8209;Dimethylprop&#8209;2&#8209;enamid keine &alpha;&#8209;Methylgruppe aufweist, zugeschrieben werden. Beide Aktivierungsparameter sind im Fall von <i>N</i>,2&#8209;Dimethylprop&#8209;2&#8209;enamid denen des <i>N</i>,<i>N</i>&#8209;Dimethylprop&#8209;2&#8209;enamid &auml;hnlich. Dies ist unerwartet, da <i>N</i>,2&#8209;Dimethylprop&#8209;2&#8209;enamid eine &alpha;&#8209;Methylgruppe aufweist. Unterschiede zwischen beiden Monomeren hinsichtlich der Konformation der Kohlenstoff&ndash;Kohlenstoff-Doppelbindung relativ zur Kohlenstoff&ndash;Sauerstoff-Doppelbindung k&ouml;nnten diese Beobachtung erkl&auml;ren.<br> Zur Bestimmung von Terminierungsgeschwindigkeitskoeffizienten wurde die Polymerisation durch einen einzelnen Laserpuls initiiert und der Monomer-zu-Polymer-Umsatz anschlie&szlig;end mittels zeitaufgel&ouml;ster Nahinfrarotspektroskopie verfolgt. Die Zeitaufl&ouml;sung ist auf 0.33&nbsp;&mu;s verbessert worden. Wiederholte Einstrahlung von Laserpulsen in Kombination mit nahinfrarotspektroskopischer Analyse liefert Terminierungsgeschwindigkeitskoeffizienten als Funktion des Grades des Monomerumsatzes. Untersuchungen der Terminierungskinetik von Prop&#8209;2&#8209;enamid, 2&#8209;Methylprop&#8209;2&#8209;enamid, <i>N</i>,2&#8209;Dimethylprop&#8209;2&#8209;enamid, <i>N</i>,<i>N</i>&#8209;Dimethylprop&#8209;2&#8209;enamid und 1&#8209;Vinylpyrrolidin&#8209;2&#8209;on wurden, aufgrund des besseren Signal-Rausch-Verh&auml;ltnisses bei hohen Dr&uuml;cken, bei 2&nbsp;000&nbsp;bar durchgef&uuml;hrt. Weitere Messungen wurden im Fall der meisten Prop&#8209;2&#8209;enamide bei Dr&uuml;cken von 500&nbsp;bar, 1&nbsp;000&nbsp;bar und 1&nbsp;500&nbsp;bar durchgef&uuml;hrt. Die dadurch erhaltenen Aktivierungsvolumina k&ouml;nnen zur Absch&auml;tzung des Terminierungsgeschwindigkeitskoeffizienten bei Umgebungsdruck verwendet werden. Die Aktivierungsvolumina der Terminierungsgeschwindigkeitskoeffizienten von <i>N</i>,2&#8209;Dimethylprop&#8209;2&#8209;enamid und von Prop&#8209;2&#8209;enamid belaufen sich auf 12.4&nbsp;cm<sup>3</sup>&middot;mol<sup>&minus;1</sup> beziehungsweise 14.3&nbsp;cm<sup>3</sup>&middot;mol<sup>&minus;1</sup>. Das Aktivierungsvolumen im Fall von <i>N</i>,<i>N</i>&#8209;Dimethylprop&#8209;2&#8209;enamid (4.9&nbsp;cm<sup>3</sup>&middot;mol<sup>&minus;1</sup>) ist kleiner als erwartet. Terminierungsgeschwindigkeitskoeffizienten von 1&#8209;Vinylpyrrolidin&#8209;2&#8209;on konnten f&uuml;r einen gro&szlig;en Bereich der Anfangsmonomerkonzentration und des Grades des Monomerumsatzes erhalten werden. Diese Daten erm&ouml;glichen eine detaillierte Analyse der Parameter, die zur Beschreibung der Monomerumsatzabh&auml;ngigkeit des Terminierungsgeschwindigkeitskoeffizienten verwendet werden. Es wird angenommen, dass der Terminierungsgeschwindigkeitskoeffizient innerhalb des untersuchten Monomerumsatzbereichs durch Segment-, Translations- und Reaktionsdiffusion kontrolliert ist.<br> Im Fall von <i>N</i>,<i>N</i>&#8209;Dimethylprop&#8209;2&#8209;enamid und 1&#8209;Vinylpyrrolidin&#8209;2&#8209;on wurden dynamische Viskosit&auml;ten von Monomer&ndash;Wasser-Gemischen bei Umgebungsdruck bestimmt, um das Verst&auml;ndnis der Terminierungskinetik zu erleichtern. F&uuml;r diese beiden Monomere wurde durch Pulslaser-induzierte Polymerisation eine gro&szlig;e Anzahl von Terminierungsgeschwindigkeitskoeffizienten in Abh&auml;ngigkeit von der Anfangsmonomerkonzentration erhalten.<br> Zur Bestimmung des Terminierungsgeschwindigkeitskoeffizienten von Prop&#8209;2&#8209;enamid in Abh&auml;ngigkeit vom Monomerumsatz wurden chemisch initiierte Polymerisationen bei Umgebungsdruck durchgef&uuml;hrt. Die erhaltenen Werte stimmen gut mit Daten &uuml;berein, die mit Hilfe von Pulslaser-induzierten Polymerisationen ermittelt wurden.<br> Untersuchungen der bin&auml;ren Copolymerisation von 1&#8209;Vinylpyrrolidin&#8209;2&#8209;on und Natriumacrylat zeigten einen ausgepr&auml;gten Einbau von Natriumacrylat in das gebildete Copolymer. Dies wurde mittels Kernspinresonanzspektroskopie gemessen. Die Monomerreaktivit&auml;tsverh&auml;ltnisse wurden mit Hilfe der Lewis&ndash;Mayo-Gleichung bestimmt.
8

SYNTHESIS AND VISCOELASTIC PROPERTIES OF GELS OBTAINED FROM LINEAR AND BRANCHED POLYMERS

Debnath, Dibyendu, Debnath 24 May 2018 (has links)
No description available.
9

SYNTHESIS AND VISCOELASTIC PROPERTIES OF GELS OBTAINED FROM LINEAR AND BRANCHED POLYMERS

Debnath, Dibyendu 24 May 2018 (has links)
No description available.

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