Acrylic resins used as polymeric binders in automotive coatings are complex copolymers containing reactive functional (often hydroxyl) groups. A better understanding of the copolymerization kinetics of these monomers is required in order to ensure uniform distribution of the functional groups among the polymer chains over the course of production. Free radical copolymerization propagation kinetics of styrene (ST) with 2-hydroxyethyl methacrylate (HEMA) and 2-hydroxyethyl acrylate (HEA) have been investigated both in bulk and solution, using pulsed-laser polymerization (PLP) combined with size exclusion chromatography (SEC) and proton NMR. All of the solvents examined (n-butanol, toluene and DMF) affect ST/HEMA copolymer composition relative to bulk polymerization, while the effects on propagation rates suggest that hydrogen bonding interactions need to be explicitly considered. Semibatch reactions of ST/HEMA, butyl acrylate (BA)/HEMA and butyl methacrylate (BMA)/HEMA have been carried out in xylene, DMF and 1-pentanol at 110 and 138 °C. The variation in monomer composition for the three solvents agrees with the kinetic studies. It was found that polymer molecular weight is strongly affected by solvent choice and operating conditions, partially due to branching reactions caused by impurities from commercial HEMA monomers. PLP and 13C-NMR analysis indicate that no backbiting occurred during polymerization of HEA, and it is shown that H-bonding disrupts the backbiting mechanism found for other acrylates. Thus, semibatch production in n-butanol can reduce branching and increase molecular weight of BA homopolymers by a factor of five compared to polymerization in xylene. / Thesis (Ph.D, Chemical Engineering) -- Queen's University, 2013-02-27 16:44:03.871

Homo- and co-polymers of acrylamide (AAm) and acrylic acid (or acrylate salt) (AA) or methacrylic acid (MAA)) are important classes of water-soluble polymers due to their numerous applications in fields such as super absorbents, additives in cosmetics, membrane technology, waste-water treatment and oil field operations. These polymers are generally made by free radical polymerization. For copolymerization reactions it is extremely important to know the details of reaction kinetics in order to ascertain the kinetic effects of different reaction parameters, which ultimately dictate final copolymer composition, microstructure and properties. The reactivity ratios for copolymerization of AAm and AA have been shown to be dependent on pH and they also change with reaction solvent. The present experimental investigation has been performed to study the kinetics of copolymerization of these monomers in aqueous and alcoholic media by considering factors such as type of initiator and solvent, and pH, in order to determine how they affect the reactivity ratios of these monomers. Reactivity ratios were determined by non-linear least squares (NLLS) and the error-in-variables-model (EVM) techniques and full conversion range kinetic investigations were carried out to confirm these values.

Homo- and co-polymers of acrylamide (AAm) and acrylic acid (or acrylate salt) (AA) or methacrylic acid (MAA)) are important classes of water-soluble polymers due to their numerous applications in fields such as super absorbents, additives in cosmetics, membrane technology, waste-water treatment and oil field operations. These polymers are generally made by free radical polymerization. For copolymerization reactions it is extremely important to know the details of reaction kinetics in order to ascertain the kinetic effects of different reaction parameters, which ultimately dictate final copolymer composition, microstructure and properties. The reactivity ratios for copolymerization of AAm and AA have been shown to be dependent on pH and they also change with reaction solvent. The present experimental investigation has been performed to study the kinetics of copolymerization of these monomers in aqueous and alcoholic media by considering factors such as type of initiator and solvent, and pH, in order to determine how they affect the reactivity ratios of these monomers. Reactivity ratios were determined by non-linear least squares (NLLS) and the error-in-variables-model (EVM) techniques and full conversion range kinetic investigations were carried out to confirm these values.

No description available.

Orientador: Liliane Maria Ferrareso Lona / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Quimica / Made available in DSpace on 2018-08-12T09:02:38Z (GMT). No. of bitstreams: 1 Nogueira_TelmaRegina_M.pdf: 1480628 bytes, checksum: 14c76a07ef8f486a5b1e73854f5c7634 (MD5) Previous issue date: 2008 / Resumo: Polimerização via radical livre controlada, também conhecida como "pseudoliving radical polymerization" tem recebido cada vez mais atenção como uma técnica para produção de polímeros com micro estrutura altamente controlada. Em particular, distribuições de pesos moleculares estreitas são obtidas, com polidispersidade muito próxima de um. Rotas convencionais para polímeros como estes têm sido polimerizações iônicas, no entanto, elas são extremamente sensíveis a impurezas e ao tipo de solvente. Processos de polimerização via radical livre, que são muito mais versáteis e robustos a impurezas, para a produção de polímeros com estruturas controladas via processo "controlado" ou "pseudo-living", têm se tornado uma importante alternativa. Como desvantagem do processo controlado aponta-se a baixa velocidade de reação quando comparada à polimerização convencional. A maioria dos trabalhos publicados sobre polimerização controlada via radicais nitróxido é feita considerando o estudo da homopolimerização de estireno. Neste projeto de pesquisa, é investigada, em nível experimental, a co-polimerização de estireno e divinilbenzeno (DVB) via polimerização controlada por nitróxidos (NMRP) usando 2,2,6,6- tetrametil-1-piperidinoxil (TEMPO) como controlador e tert-butilperóxido-2-etilhexil carbonato (TBEC) como iniciador. O DVB funciona como gerador de ramificações na cadeia polimérica, melhorando as propriedades do estireno como resistência a solvente e ao impacto. O TBEC foi utilizado em substituição a iniciadores mais convencionais como o 2,2-azo-bis-iso-butironitrila (AIBN) e peróxido de benzoíla (BPO), com o objetivo de acelerar a velocidade de reação, tentando manter o sistema controlado. Todos os experimentos foram feitos em ampolas. Para um melhor entendimento deste sistema, muitos experimentos foram realizados a diferentes temperaturas, concentrações de divinilbenzeno, concentrações de iniciador e razões molares entre as concentrações de controlador e iniciador. A conversão do monômero foi obtida por gravimetria e o polímero foi caracterizado através de Cromatografia de Permeação em Gel (GPC). Foi demonstrado que o TBEC foi capaz de aumentar a velocidade de reação em relação ao BPO e, em algumas condições operacionais utilizadas, polidispersidades próximas da unidade foram obtidas. / Abstract: Living free radical polymerization, also known as "pseudo-living radical polymerization" has received more and more attention as a technique for the production of polymers with micro structure highly controlled (narrow molecular weights distributions and polydispersity index close to one). Conventional routes to obtain polymer like this have been ionic polymerizations, however, they are extremely sensitive to impurities and solvents. Free radical polymerizations, which are more versatile and robust to impurities, for the production of polymers with controlled structures by "controlled" or "pseudo-living" process, have become an important alternative. As a disadvantage of the controlled process can be pointed the low reaction rate when compared to the conventional process. Most of the published papers about nitroxide mediated living free radical polymerization consider the homopolymerization of styrene as case study. In this research, the co-polymerization of styrene and divinylbenzene (DVB) by living free radical polymerization (NMRP) is investigated in experimental level. The stable radical used was 2,2,6,6-tetramethyl-1-piperidinoxyl (TEMPO). The initiators used in this work were tertbutylperoxy- 2-ethylhexyl carbonate (TBEC) and benzoyl peroxide (BPO). DVB acts as a branching generator, improving the properties of the styrene as the solvent and impact resistance. TBEC was used in substitution to conventional initiators as 2, 2-Azo-bisisobutyronitrile (AIBN) and BPO, with the aim of accelerating the reaction rate, trying to keep a controlled/living system. All the experiments were performed in ampoules. To better understand this system, many experiments were performed at different temperatures, divinylbenzene concentrations, initiator concentrations and molar ratios between controller and initiator. Conversion was obtained by gravimetric method and the polymer was characterized by Gel Permeation Chromatograph (GPC). It was observed that, at certain operating conditions, the TBEC initiator was able to produce copolymers with polydispersity close to unity in a much faster velocity when compared to BPO. / Mestrado / Processos Quimicos / Mestre em Engenharia Química

El objetivo de este trabajo se centró en la síntesis de nuevos catalizadores homogéneos de paladio para la reacción de copolimerización de monóxido de carbono con estireno. El interés de esta reacción catalítica radica en las propiedades de los copolímeros a que da lugar, que son termoplásticos bio- y fotodegradables. La ventaja de usar catalizadores homogéneos para la copolimerización, respecto a la polimerización radicalaria, es que en los copolímeros obtenidos las moléculas de monóxido de carbono y estireno se encuentran insertadas de una manera perfectamente alternada y regular. Para ello la utilización de precursores organometálicos de paladio(II) que posean un ligando quelato, ha sido descrita como la mejor forma de obtener sistemas activos.La influencia de la naturaleza del ligando quelato en la actividad del precursor catalítico, en especial la de sus átomos dadores, ha llevado a la elección de ligandos bidentados nitrógeno- y azufre-dadores para la realización de este trabajo. Así se ha escogido una serie de ligandos ditioéter, previamente utilizados en otros procesos catalíticos, así como ligandos piridina-pirazol y pirimidina-pirazol para estudiar su efecto sobre el metal y sobre la actividad del catalizador en la reacción de copolimerización. Además con el objeto de hacer un estudio sistemático de la influencia del ligando se ha diseñado y sintetizado una nueva familia de ligandos nitrógeno-dadores piridina-imidazolina de simetría C1. Estos nuevos ligandos piridina-imidazolina poseen la ventaja de ser fácilmente modificables, dando lugar a series de ligandos con variaciones estructurales sistemáticas.La coordinación de todos estos ligandos a paladio ha dado lugar a nuevos complejos neutros de fórmula [PdClMe(L-L)] y catiónicos de fórmula [PdMe(NCMe)(L-L)][X]. El análisis de la estereoquímica de los nuevos complejos sintetizados se realizó por RMN, observándose claras diferencias en función de ligando utilizado. Asimismo en algunos de los casos la obtención de monocristales ha hecho posible el análisis de la estructura en estado sólido de algunos de estos complejos, mediante difracción de rayos-X. La utilización de los complejos catiónicos de fórmula [PdMe(NCMe)(L-L)][BAr'4] como precursores de catalizador para la reacción de copolimerización ha dado lugar a la obtención de sistemas activos, de los que pueden extraerse las siguientes conclusiones:Los complejos de paladio que contienen ligandos ditioéteres son activos como precursores de catalizador para la reacción de copolimerización de 4-tert-butilestireno con monóxido de carbono, como se explica en el Capítulo 3. Sin embargo, los complejos son poco estables en atmósfera de CO, reduciéndose a paladio metálico. Los copolímeros obtenidos con estos catalizadores presentan microestructuras muy variables dependiendo del ligando azufre-dador utilizado. Se han podido obtener copolímeros isotácticos escogiendo el ligando ditioéter con la rigidez del esqueleto y con el tamaño de quelato apropiados, concretamente con el ligando (-)-deguspri.El Capítulo 4 describe la síntesis de nuevos complejos catiónicos de Pd(II) que contienen ligandos nitrógeno-dadores derivados del pirazol. La utilización de estos ligandos planos lleva a la obtención de complejos muy activos en la reacción de copolimerización, debido a sus propiedades estéricas y electrónicas. El estudio de la actividad de los precursores catalíticos y del peso molecular de los copolímeros obtenidos, en función del tiempo de reacción ponen de manifiesto que se trata de sistemas de polimerización "living". Los polímeros obtenidos son, en todos los casos, de elevado peso molecular y sindiotácticos.La síntesis de los nuevos ligandos nitrógeno-dadores derivados de la imidazolina, que poseen variaciones estructurales sistemáticas, se presenta en el Capítulo 5. La coordinación de estos ligandos a paladio ha dado lugar a complejos neutros [PdClMe(N-N')] que presentan la misma estereoquímica independientemente del ligando utilizado. Algunos de estos complejos han sido analizados en estado sólido por difracción de rayos-X.Se han observado diferencias en las distancias de coordinación del ligando al metal, en función del substituyente que posea la imidazolina en el nitrógeno amínico. Los complejos catiónicos sintetizados presentan, en disolución, notables diferencias estereoquímicas en función de la basicidad de los ligandos nitrógeno-dador utilizados. Así pues se han obtenido selectivamente estereoisómeros en función del ligando utilizado. La actividad de estos complejos catiónicos como precursores catalíticos para la reacción de copolimerización se ha observado que depende,fundamentalmente, de la basicidad del ligando, siendo más activos los catalizadores que poseen coordinados los ligandos menos básicos. En función del precursor utilizado es posible la síntesis de copolímeros con distinto grado de estereoregularidad. Así, precursores que poseen ligandos con substituyentes en el nitrógeno amínico que retiran densidad electrónica dan lugar a copolímeros sindiotácticos. En el caso de que los ligandos posean substituyentes dadores de densidad electrónica no se ha podido establecer una relación directa entre el precursor y la tacticidad del polímero. El estudio de la reactividad de los precursores catalíticos con CO ha sido realizada "in-situ" por RMN y ha puesto de manifiesto que los complejos formados son acilos-carbonilos de paladio de fórmula [Pd(COMe)(CO)(N-N')][X].Los precursores de catalizador que contienen ligandos nitrógenodadores,derivados tanto del pirazol como de la imidazolina, han resultado ser activos en la reacción de terpolimerización de tert-butilestireno y etileno con monóxido de carbono. Las diferencias estructurales de los ligandos utilizados tienen una marcada influencia en la reactividad de los complejos de paladio con los distintos alquenos. Ésto ha llevado a la obtención de terpolímeros con diferente concentración de monómeros en función de las propiedades estructurales del ligando nitrogenado utilizado. / The development and study of new palladium catalysts for the copolymerization of 4-tert-butylstyrene with carbon monoxide was the main objective in the present thesis. The role played by the chelating ligands and in particular by their donating atoms is known to be fundamental in this catalytic process and therefore sulfur and nitrogen-donating ligands were studied. As a result from this study, the following conclusions can be drawn:The new palladium(II) neutral and cationic complexes containing bis(thio)ethers as chelating ligands, synthesized in Chapter 3, show different behavior in solution depending on the rigidity of the ligand. The cationic complexes are precursors for the copolymerization of CO/4-tertbutylstyrene although they are quite unstable under carbon monoxide pressure and get reduced to inactive palladium metal. By choosing chiral bis-(thio)ethers with the appropriate backbone rigidity, good stereocontrol of the styrene insertion in the polyketone chain may be obtained.In Chapter 4 the coordination of a family of Cs-symmetrical pyrazolcontaining bisnitrogen ligands to palladium-methyl cationic complexes leads to different stereoisomers depending on the steric hindrance of the bisnitrogen ligand. They behave as active precursors for the copolymerization reaction and allow the synthesis of syndiotactic polyketones, irrespectively of the stereochemistry of the precatalyst. Under mild copolymerization conditions the pyrazol-containing catalysts are an example of living copolymerization catalysts.Chapter 5 deals with the synthesis of new chiral N1-substituted imidazolines which allow tuning the electronic properties of the metal to which they are coordinated. The differently substituted C1-symmetrical pyridine-imidazolines may lead to the selective synthesis of palladium cationic stereoisomers depending on the basicity of the ligand. Similarly under carbon monoxide atmosphere, palladium-acyl stereoisomers may be selectively obtained. When the different stereoisomers are used as precatalysts for the copolymerization of CO and 4-tert-butylstyrene, polyketones with different degrees of stereoregularity may be obtained.The combination of a pyridine or pyrimidine ring with a 5-membered nitrogen containing heterocycle (pyrazol or imidazoline) leads to effective achiral or chiral ligands, respectively, for the CO/4-tertbutylstyrene copolymerization and also CO/ethene/4-tert-butylstyrene terpolymerization reactions, as shown in Chapter 6. The palladium precatalysts with pyrazol-containing ligands are more stable under co- and terpolymerization conditions than the imidazoline-derived ones. The steric hindrance caused by the chiral imidazoline ligands may be responsible for the low reactivity of the palladium species towards 4-tert-butylstyrene,while the insertion of ethylene is more favored. This reactivity is reversed when less steric hindered nitrogen ligands are used.

Current industrial processes for the production of polycarbonates, a thermoplastic valued for commercial applications, leave much to be desired from an environmental viewpoint. Research into alternative methods for production of polycarbonates has focused on the copolymerization of carbon dioxide and epoxides for the benefits of eliminating phosgene as a reagent, and for the economic impact of incorporating CO2 as a low cost C1 feedstock. Early work in this field focused on the use of zinc-derived catalysts, but recent studies indicate that chromium complexes of the salen (N,N-bis-(salicylidene)-1,2-ethylene diimine) family of ligands are far superior to the zinc complexes in terms of reactivity and diminishing the formation of unwanted byproducts. Concomitant to the studies of chromium salen complexes, investigations of main-group salen metal complexes were carried out. Aluminum complexes were able to produce polycarbonate in the presence of tetrabutyl ammonium salts and neutral Lewis bases. Gallium complexes were essentially inactive for generating any product. Tin(IV) complexes were active for the production of polyether, the result of homopolymerization of epoxide without CO2 insertion. Tin(II) complexes generated the monomeric cyclic carbonate product but no copolymer. An additional aspect of research relative to this field of study is the development of polymeric materials from several different epoxide monomers. The complex [hydrotris(3-phenyl-pyrazol-1-yl)borate]Cd(II) acetate was used to study the thermodynamics of the binding of a series of potential epoxide monomers to a metal center via 113Cd NMR. Activation of the epoxide by a metal center was found to not play a significant role in the ability of the complex to be subsequently ring-opened for polymerization. A final relevant area of study involved the synthesis of cadmium analogues of Fe/Zn double metal cyanide (DMC) complexes. Heterogeneous DMCs are well known in patent literature as excellent catalysts for the production of polycarbonates and cyclic carbonates from CO2 and epoxides. Previous studies on homogeneous Fe/Zn DMCs have only provided cyclic carbonate. Cd analogues of these species provide a convenient NMR handle for studies on the activity of the metal centers in presence of an epoxide and by changes to the DMC structure.

The ability to utilize cheaper starting materials in the synthesis of commercially important materials has been a goal of scientists since the advent of the chemical industry. The ideal situation would be one in which by combining the correct proportions of hydrogen, nitrogen, carbon and oxygen that virtually anything from simple sugars to complex polymers could be produced. Unfortunately, such processes are flights of fancy often reserved for movies and television shows. On a more realistic level, the utilization of simple molecules and a transition metal catalyst has been a process that industry has exploited for many years. The most easily identifiable process is that for polyolefin production, that employs homopolymerization of simple monomers such as ethylene and catalysts ranging from Ziegler-Natta to metallocene type catalysts. On a more difficult level copolymerization reactions require a delicate balance between two competing reactions and as a result these reactions have been much less successful. For over a decade now the Darensbourg Research Laboratories have focused on utilizing another simple molecule: carbon dioxide. Carbon dioxide is a cheap, inert, nontoxic starting material that appears to be an ideal monomer. Although simplistic, CO2 is also very stable and its utilization in polymerization reactions have proven to be quite complex. In order for us to facilitate these reactions we employ both a transition metal catalyst and a comonomer. Epoxides act as an effective comonomer because the thermodynamic energy gained from breaking the strained three membered epoxide ring overcomes the stability of CO2 and allows the copolymerization reaction to occur. We have demonstrated a great deal of success with this process, most of which will be mentioned throughout this report. The majority of this dissertation will detail our use of salen complexes to optimize this copolymerization process, in order to further the use of CO2 as a viable source of C1 feedstock. Herein, I will illustrate how we have obtained more than a 100 fold increase in the rate of polymer formation as well as detailed mechanistic data that will provide a basis for future catalyst design studies.

Solvent-free peroxide-initiated polymer modifications are widely used to improve the physical and/or chemical properties of commodity plastics and elastomers. Although the reactions that underlie polymer grafting are known, our understanding of H-atom transfer reactions in this context is incomplete. Fundamental questions remain unanswered, such as the difference in reactivity between different polymers (polyethylene versus polypropylene and polyisobutylene) and differences in the regiochemical outcomes of grafting reactions upon them. Herein, experimental data pertaining to the H-atom transfers involved in polyolefin graft modifications were obtained to improve our fundamental understanding of these reactions by using radical-trapping techniques and quantum chemical calculations. In this project, experimental measurements of the efficiency of H-atom abstraction by t-butoxyl radicals from polyolefins, and suitable model compounds such as pentane, 2,4-dimethylpentane and 2,2,4,4-tetramethylpentane were determined. Insight is gained from alkyl-trapping experiments to quantify the relative reactivities of the primary, secondary and tertiary positions of the model compounds. Experimental data were compared to quantum chemical calculations, which revealed that entropic effects dictate the regioselectivity and preclude abstraction at the secondary position in favour of the less enthalpically-favourable primary abstraction site. MP2 and CBS-QB3 level calculations were able to reproduce experimental trends in model compound reactivity, while the highly common B3LYP density functional, used in other investigations on the subject, could not. / Thesis (Master, Chemical Engineering) -- Queen's University, 2011-10-20 16:48:38.083

Vinyl ester oligomers diluted with styrene are important matrix resins for thermosetting polymer composites. A major objective of this work has been to study the chemistry and kinetics of the cure reactions of vinyl ester resins at elevated curing temperatures, which are consistent with typical composite processing conditions. The crosslinking reaction of vinyl ester resins was studied by FTIR and the loss of the carbon-carbon double bonds of the methacrylate (943 cm-1) and styrene (910 cm-1) were followed independently. A small background absorbance overlapping the absorbance at 943 cm-1 was subtracted from all spectra collected as a function of reaction time to quantify conversions. Copolymerization reactivity ratios of styrene and terminal methacrylates on vinyl ester oligomers were calculated to be rs = 0.36 ± 0.05 and rm = 0.24 ± 0.1 from early conversion data obtained at 140°C on a series of resins with systematically increasing levels of styrene. The composition data were analyzed using the integrated form of the copolymerization equation and assuming a terminal reactivity model to predict copolymer compositions throughout the reactions. These curves agreed well with the experimental data even at high conversion levels. Another important part of this research was to study structure-property relationships of vinyl ester resins. Characteristics of vinyl ester resins and networks such as shrinkage, viscosity, crosslink density, glass transition temperature, gel swelling, and toughness have been studied. The shrinkage of vinyl ester resins during cure was calculated according to density measurements to be 4% - 10% depending on styrene content. It was found that the chain length of vinyl ester oligomers strongly affects the properties of the networks. For vinyl ester resins with longer lengths (Mn = 1000 g/mol), crosslinked networks have higher fracture toughness values and lower Tg's. Finally, the synthesis, cure reactions and toughness of a new low viscosity vinyl ester resin were also investigated in this work. The new oligomer has a structure with which the hydroxyl groups on the backbone are replaced by methyl groups. They could be processed without a diluent. The cure reactions of the new resin were studied by FTIR, DSC and 13C-NMR. / Ph. D.