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Yes / We have studied the tensile behaviour of polycarbonate at large strains below the glass transition temperature. Experiments have been carried out at a series of constant temperatures and also under conditions of falling temperature. The specimens neck with a natural draw ratio of ~2, and the study focuses mainly on the necked material. Isothermal experiments reveal an elastic mechanism that initiates beyond the natural draw ratio. A model consisting of an Eyring process and two Gaussian elastic mechanisms is shown to be applicable to both the isothermal and anisothermal stress relaxation and stress-strain results. The same model also produces reasonable estimates of the stresses generated during the necking process. In addition, a simple relationship between isothermal and anisothermal stress relaxation is demonstrated.

La photopolymérisation est un procédé en plein essor qui permet d’accéder à des matériaux polymères, notamment sous la forme de films ou de revêtements. Néanmoins, celle-ci est majoritairement basée sur un mécanisme de polymérisation radicalaire qui proscrit l’obtention de matériaux totalement biodégradables. Aussi, au cours de cette thèse, nous nous sommes intéressés à la photopolymérisation par ouverture de cycle (photoROP) d’esters et de carbonates cycliques à l’aide de deux grandes familles de photogénérateurs de bases (PBGs). Tout d’abord, des PBGs, pouvant libérer des superbases de type amidine et guanidine cycliques ont été employées pour mener efficacement la photoROP du L-LA et du TMC en solution. Puis, nous nous sommes attachés à développer, sur le modèle des photobases précédentes, de nouveaux PBGs qui libèrent sous irradiation UV des carbènes N-hétérocycliques (NHCs). La libération des NHCs à partir de ces « NHCs photolatents » a été prouvée par RMN 1H et par la formation d’adduits NHC.CS2. De même, ces PBGs se sont révélés actifs pour la photoROP du L-LA et du TMC en solution, mais avec une plus faible efficacité que les PBGs précédents. En effet, les cinétiques de polymérisation sont lentes du fait de la présence de CO2 dans le milieu (libéré lors de l’irradiation UV) qui conduit à la formation d’adduit NHC.CO2 inactif en ROP. Ainsi, la photobase la plus performante, libérant du TBD, a été employée afin d’effectuer la photoROP en masse d’esters cycliques liquides (ε-CL, δ-VL et un mélange innovant L-LA/TMC). Finalement, des réseaux ont été formés par incorporation dans le milieu réactionnel d’un monomère bifonctionnel, permettant d’obtenir sur demande (contrôle temporel) des matériaux réticulés potentiellement entièrement biodégradables. / Photopolymerization is a growing process allowing preparing polymer materials, notably in the form of films or coatings. Nevertheless, it is mostly based on a radical polymerization mechanism that prevents obtaining fully biodegradable materials. The goal of this PhD work was thus to develop the photopolymerization of cyclic esters and carbonates by using two families of photobase generators (PBGs). First, already described PBGs, releasing cyclic amidine and guanidine-type superbases, were effectively employed to carry out the photopolymerization of L-LA and TMC in solution. Then, taking previous PBGs as models, we developed new PBGs able to release N-heterocyclic carbenes (NHCs) under UV irradiation. The release of NHCs from these “photolatent NHCs” was proven both by 1H NMR and by the formation of NHC.CS2 adducts. These PBGs also proved to be active for the ROP of L-LA and TMC in solution, but to a lesser extent than previous photobases. Indeed, slower kinetics of polymerization were observed, which was attributed to the presence of CO2 in the reaction medium (CO2 released by photodegradation of the PBG) that leads to the formation of NHC.CO2 adduct (inactive for ROP). Thus, the most efficient photobase (releasing TBD) was employed to carry out the bulk photopolymerizations of liquid cyclic esters (ε-CL, δ-VL and even an innovative L-LA / TMC mixture). Finally, polymer networks have been formed by incorporating a bifunctional monomer into the reaction medium, allowing the preparation “on demand” (temporal control) of potentially fully biodegradable materials in a one-pot process.

Dissertation (Ph. D.)--University of Akron, Dept. of Polymer Engineering, 2009. / "May, 2009." Title from electronic dissertation title page (viewed 11/27/2009) Advisor, Avraam I. Isayev; Committee members, James L. White, Thein Kyu, Kevin Kreider, Shi-Qing Wang; Department Chair, Sadhan C. Jana; Dean of the College, Stephen Cheng; Dean of the Graduate School, George R. Newkome. Includes bibliographical references.

Polycarbonates are found in a variety of common products in daily life due to their favorable mechanical and electrical properties. In addition, they are widely used in biomedical areas due to their stability and biological inertness. Therefore, the production of polycarbonates became an important industrial process in the past decades. However, the current industrial process usually requires toxic phosgene gas as a starting material. Thus, the environmentally benign route by using metal catalyzed couplings of epoxides and CO_(2) to produce polycarbonates has received attention from researchers. In this dissertation, metal catalyzed CO_(2)/cyclic ether copolymerization, depolymerization of polycarbonates, and the equilibria between polycarbonate and corresponding six-membered cyclic carbonate will be investigated. First, the Co(III) catalyzed copolymerizations of CO_(2) and various epoxides with electron-withdrawing substituents to afford polycarbonates are examined. Comparative kinetic studies were performed via in situ infrared measurements as a function of temperature to assess the activation barriers for the production of cyclic carbonate versus copolymer involving electronically different epoxides: styrene oxide, epichlorohydrin, and propylene oxide. Thermodynamically stable cyclic carbonate byproducts are produced during the course of the reaction from the degradations of propagating polymer chains. The depolymerization reactions of several polycarbonates produced from the completely alternating copolymerization of styrene oxide, epichlorohydrin, propylene oxide, cyclohexene oxide, indene oxide, and cyclopentene oxide with carbon dioxide have been investigated. Various reaction pathways can be found under different reaction conditions, including process involving chain-end backbiting and radical intermediates. Temperature-dependent kinetic studies have provided energy of activation barriers for cyclic carbonate formation. In addition, the generated monomeric materials from the degradation of select polycarbonates show the possibility of chemical recycling of plastic waste. For the copolymers made from CO_(2) and oxetane derivatives, this study focuses on the influence of steric hindrance in the 3-position of the monomer oxetane. The (salen)CrCl/onium salt catalyzed coupling reactions of these oxetane derivatives and carbon dioxide are reported. Depolymerizations of copolymers to their corresponding cyclic carbonates were also studied. In addition, several six-membered cyclic carbonates were synthesized to examine their equilibria between monomeric cyclic carbonates and their corresponding polycarbonates.

Thesis (M.S.)--Oregon State University, 2008. / Printout. Includes bibliographical references. Also available on the World Wide Web.

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The use of waste gas such as carbon dioxide (CO2) to prepare useful and valuable polymers benefits both the economy and the environment. Various strategies have been developed to reduce CO2 emission as well as to transfer CO2 into high-value products. CO2/epoxide copolymerization is one of the most promising methods of not only reducing the CO2 emission from the atmosphere but also producing biodegradable CO2-based materials that are CO2 as source-abundant, renewable, cheap, non-flammable and non-toxic. However, the activation of CO2 is one of several problems associated with the polymerization of CO2 due to its stability as a thermodynamic end product. Herein, my dissertation describes the effectiveness of new lithium/phosphazene complexes to generate highly active species for CO2/epoxide copolymerization and to capture/activate CO2 molecules for the nucleophilic attack of the active species. Well-defined polycarbonates and polycarbonate-based block copolymers are produced that have control of molecular weights, unimodal distributions and narrow molecular weight distributions (Chapter 3 and 4). Besides, these complexes provide access to prepare CO2-based triblock copolymers that are powerful candidates to serve as the next generation of thermoplastic elastomers (Chapter 4). Additionally, these complexes are applied for the anionic polymerization of petrochemical-based sources such as styrene and dienes producing polymers in faster rate of polymerization with control of molecular characteristics (Chapter 2). A general introduction of polymers and their classification based on composition, chemical structure, mechanical properties, degradability, source, applications, and preparative methods, is covered in Chapter 1

Cette thèse porte sur la valorisation de dérivés d’acides gras dans l’objectif d’élaborer des matériaux polycarbonates aliphatiques (PCAs) bio-sourcés originaux. Dans cette optique, deux plateformes de carbonates cycliques à 6 chaînons (6CCs) ont été synthétisés en utilisant des voies d’accès impliquant soit la formation d’un intermédiaire de type malonate ou un couplage entre un acide gras et le 2-amino-1,3-propanediol. La polymérisation par ouverture de cycle de ces monomères a été étudiée. La première plateforme de 6CCs a été polymérisée en présence de Sn(Oct)2 comme catalyseur, donnant accès à des polycarbonates de faible Tg allant de -61°C jusqu’à-26°C du fait de longues chaines latérales pendantes. La polymérisation de la seconde plateforme de6CCs a été effectuée de manière contrôlée en utilisant un système catalytique composé de la DBU et d’une thio-urée. Tirant profit de ces polycarbonates aliphatiques bio-sourcés linéaires porteurs d’insaturations, des matériaux originaux réticulés ont été synthétisés. Plusieurs méthodes de réticulation ont été testées telles que le couplage thiol-ène irréversible, la réaction de Diels-Alder thermo-réversible et la cyclo-addition photo-réversible [2+2] entre deux groupements cinnamate.Ainsi, des PCAs réticulés issus d’acides gras ont été synthétisés et caractérisés; ces derniers possèdent des propriétés physico-chimiques modulables selon la nature des monomères de départ etla densité de réticulation des réseaux. / Fatty acids were derivatized with the objective to design bio-based aliphatic polycarbonate(APC) materials. To that purpose, two platforms of lipidic 6-membered cyclic carbonates were prepared following synthetic routes either involving the ring-closure of a malonate intermediate or the coupling reaction between a fatty acid and 2-amino-1,3-propanediol. The ring-openingpolymerization (ROP) of these cyclic carbonates was next investigated. The first platform of 6CCswas polymerized in the presence of Sn(Oct)2 as catalyst, yielding low Tg aliphatic polycarbonates ranging from -61°C to -26°C with respect to the size of the pendant aliphatic side chains. The polymerization of the second lipidic 6CC platform was performed in a controlled fashion using DBU/Schreiner thiourea as catalytic system. Taking advantage of the presence of unsaturation functions on the linear bio-based APCs, cross-linked polycarbonate materials were then prepared.Several cross-linking methods were tested such as the irreversible thiol-ene coupling, the thermoreversible Diels-Alder reaction and the photo-reversible [2+2] cyclo-addition reaction between two cinnamate moieties. Fatty acid-based cross-linked APCs were thus designed and characterized; the latter exhibit tunable physico-chemical properties as a function of the monomer structure and the cross-linking density.