A family of C2-symmetric catalysts was designed and synthesized with the intent to polymerize propylene. The catalyst was designed to be C2-symmetric for the specific goal that the catalyst would have two identical sites for the propagation of the polymer and therefore eliminate some of the stereoerrors that occur in the propagation of the polymer chain. This catalyst would also operate under simple enantiomorphic site control and therefore the insertion of the monomer would be governed by the ligand surrounding the active site. The ligands were synthesized with increasing degrees of steric bulk with the intention to determine if a catalyst system could generate elastomeric polypropylene. Enantiomorphic site control polypropylene utilizes statistical methods to determine the Si and Re content of a given polymer chain as a function of the variable E. Polypropylene samples generated by the catalyst family were analyzed using high temperature pentad analysis of the methyl region to calculate the E value. The goal was to observe E to be equal to 0.78 provided that the number molecular weight of the polymer was 100,000. The catalyst systems generated polymers with values higher and lower than the desired 0.78, indicating too high or too low enantioselectivity of the catalyst systems respectively at Tp = 0°C.

A family of C2-symmetric catalysts was designed and synthesized with the intent to polymerize propylene. The catalyst was designed to be C2-symmetric for the specific goal that the catalyst would have two identical sites for the propagation of the polymer and therefore eliminate some of the stereoerrors that occur in the propagation of the polymer chain. This catalyst would also operate under simple enantiomorphic site control and therefore the insertion of the monomer would be governed by the ligand surrounding the active site. The ligands were synthesized with increasing degrees of steric bulk with the intention to determine if a catalyst system could generate elastomeric polypropylene. Enantiomorphic site control polypropylene utilizes statistical methods to determine the Si and Re content of a given polymer chain as a function of the variable E. Polypropylene samples generated by the catalyst family were analyzed using high temperature pentad analysis of the methyl region to calculate the E value. The goal was to observe E to be equal to 0.78 provided that the number molecular weight of the polymer was 100,000. The catalyst systems generated polymers with values higher and lower than the desired 0.78, indicating too high or too low enantioselectivity of the catalyst systems respectively at Tp = 0°C.

No description available.

A series of stereoregular polymers including atactic, syndiotactic and isotactic poly 4(N, N-diphenyl)styrene (PNNDPS) and poly 4(N, N-ethylphenyl)styrene (PNNEPS) were synthesized to exam the tacticity effect on the photoluminescence (PL) behavior. Also, different degrees of the regularity as well as the chemical modification of the fluorophor were explored in the stereoregular polymers. Because of the increase of the steric hindrance among the bulky triphenylamine pendants in the polymer chains, a red shift of the PL emission with an accompanying increase in the emissive intensity was found in contrast to the weakened emission of triphenylamine monomers. In solution state, the PL spectra of these stereoregular polymers reveal multiple PL emissive bands including monomeric and aggregation emissions as evidenced by the time-resolved lifetime measurement. Because of the huge triphenylamine pendants, the triphenylamine pendants attached on the iPNNDPS17 (mmmmmm~50%) might encounter higher steric hindrance than that in the sPNNDPS23 (rrrrrr~59%) due to the stereoregularity evidenced by simulation. Accordingly, the iPNNDPS17 (mmmmmm~50%) exhibits more emissive intensity than the sPNNDPS23 (rrrrrr~59%) due to the effective blockage of the intramolecular rotation of the phenyl blade i.e., the restriction of intramolecular rotation (RIR). Accordingly, the RIR-active PNNDPS is highly sensitive to the temperature variations. The chemical modification of the fluorophor was carried out to examine the effect of the chemical structure. By comparison, the sPNNDPS2 (rrrrrr~70%) with high regularity exhibits much higher emissive intensity than the sPNNDPS23 (rrrrrr~59%) with low regularity due to the less solubility. However, more intense PL emission can be found in the sPNNEPS17 than aPNNEPS8 due to the ethyl substitution of the fluorophor. In aggregation solution, with the increase of the poor water contents, the PL emission decreases significantly in the sPNNDPS23 (rrrrrr~59%) and sPNNDPS2 (rrrrrr~70%) due to the formation of H-aggregate in which extra energetic loss is conducted. By contrast, the PL spectra display that the emissive intensity decreases first as fw=0.1~0.5 and then intensifies later as fw=0.6~0.9. This might be resulted from the competition between the £k-£k interaction and RIR effect. Interestingly, the PL emissive intensity drops down significantly in the sPNNEPS, whereas the PL emissive intensity is almost unchanged in the aPNNEPS8 with the increase of the poor water contents. We suggest that because the aPNNEPS8 might contain both syndiotactic and isotactic configurations, the isotactic configurations having the ethyl group pointing out of the plane may prevent the formation of the £k-stacking between the fluorophors. The PL behavior in thin film is also explored for these stereoregular polymers. After slow cooling from melt, the crystalline sPNNDPS2 (rrrrrr~70%) thin film exhibits very strong emission in comparison with the thin film after quenching from melt, indicating the crystallization-induced emission enhancement. Although the iPNNDPS17 (mmmmmm~50%) is noncrystallizable as evidenced by differential scanning calorimetry (DSC) and polarized light microscope (PLM), the PL emissive intensity of the iPNNDPS17 (mmmmmm~50%) thin film is significantly stronger after slow cooling from melt than that after quenching from melt. We suggest that this might be attributed to the free volume effect varied with the thermal history associated with the steric hindrance. Notably, this enhanced PL emission in the iPNNDPS17 (mmmmmm~50%) thin film is extremely larger than that in the sPNNDPS23 (rrrrrr~59%) and aPNNDPS8, indicating the stereoregularity effect associated with the RIR effect. By contrast, this free volume effect is not significant in the PNNEPS thin film due to the flexible ethyl substitutions. As a result, the stereoregular polymers with different tacticities and regularities indeed exhibit distinct PL behavior in solution and thin film.

Thesis advisor: Jeffery A. Byers / This dissertation focuses on the development of iron-based polymerization catalysts for use in the production of high commodity polymers, polyethylene and poly(lactic acid). Chapter one establishes the current landscape of the plastic market and outlines the advantages to developing iron-based catalysts. Chapter two then explores the use of bis(pyridinylimino)isoindolate-ligated iron complexes as a family of ethylene polymerization catalysts possessing distinctive mechanistic behavior. Chapter three moves to focus on the polymerization of stereoregular poly(lactic acid) from an achiral bis(imino)pyridine-ligated iron precatalyst. The mechanism for the desymmetrization of the catalyst is further detailed, and new avenues for enhancing the behavior of the reaction are discussed. Chapter four details the development of conditions for the rapid chain transfer polymerization of lactide and cyclohexene oxide, offering another tool by which value and complexity may be added to polymerization reactions carried out by this family of bis(imino)pyridine-ligated iron complexes. Finally, chapter five leverages the known redox-switchable features of bis(imino)pyridine-ligated iron complexes to develop reaction conditions for the controlled branching of poly(lactic acid) in a one-pot polymerization reaction. / Thesis (PhD) — Boston College, 2019. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Chemistry.

L’utilisation de séquences RMN de diffusion permet d’étudier les échanges dynamiques du PEO en tant que petite molécule qui diffuse à travers les parois de nanocapsules creuses de PMMA afin de maîtriser son relargage en fonction du milieu. Ces objets nanostructurés étant élaborés via la formation de stéréocomplexe entre les PMMA isotactique et syndiotactique dans l’acétonitrile, une étude préliminaire a été consacrée à l’influence d’interactions PMMA/PEO sur la morphologie des nanocapsules creuses.Dans un premier temps, nous avons étudié les interactions stéréospécifiques au sein des systèmes binaires PMMA stéréorégulier/PEO dans le chloroforme, solvant non complexant, puis dans l’acétonitrile. L’utilisation de la méthode RMN DOSY nous a donc permis de mettre en évidence la formation d’une double distribution de nanoagrégats de tailles et de composition contrôlés. Le PEO étant présent dans une des populations de nanoagrégats, sa présence induit et stabilise les agrégats de PMMA. Les interactions PMMA/PEO dépendantes de la tacticité du PMMA sont responsables de ces nanostructures. Elles sont non seulement contrôlées par la tacticité du PMMA mais également par la concentration et la masse molaire du PEO. Dans le chloroforme, un modèle d’interaction en trois étapes en fonction de la concentration en PEO, en a été déduit soulignant l’effet prépondérant de la conformation des polymères sur ces interactions. De plus, une généralisation dans plusieurs solvants de ce modèle d’interactions stéréospécifiques a permis de mettre en évidence la corrélation entre la longueur des séquences isotactiques ou syndiotactiques, leurs conformations et la masse molaire du PEO. Dans un second temps, nous avons pu en déduire une corrélation avec la diminution du phénomène de stéréocomplexation dans les systèmes stéréocomplexe du PMMA/PEO/CD3CN sur la base des interactions observées entre les deux polymères en solution dans l’acétonitrile. Le PEO perturbe en partie la formation du stéréocomplexe, permettant ainsi de mettre en évidence l’influence de la présence de PEO sur la structure des nanocapsules creuses de PMMA et son effet désintégrant.Ces études ont montré que les mécanismes de diffusion à travers les parois utilisés dans les systèmes à relargage contrôlé ne peuvent faire l’impasse sur l’analyse préalable des interactions potentielles entre les molécules sondes et la structure des parois polymériques. En effet, ces interactions peuvent fortement modifiés la structure de ces containers et les mécanismes de diffusion doivent prendre quantitativement en compte ces effets pour être efficients.Ces travaux laissent entrevoir la démarche scientifique à suivre pour le développement de modèle de libération contrôlée de molécules actives à travers les membranes des nanocapsules, elles-mêmes incluses dans des systèmes polymériques. / Use of NMR pulse sequences to measure diffusion permits to study the dynamic exchange of PEO as a small molecule that diffuses through hollow PMMA nanocapsules walls in order to control its release according to the environment. These nanostructured objects being composed of stereocomplex between isotactic and syndiotactic PMMA in acetonitrile, a preliminary study was devoted to the influence of PMMA/PEO interactions on the morphology of hollow nanocapsules.Firstly, we studied stereospecific interactions in binary systems stereoregular PMMA/PEO in chloroform, non-complexing solvent, and acetonitrile. The use of the DOSY NMR method allowed us to demonstrate the formation of a double distribution of nanoaggregates of controlled size and composition. PEO is present in a population of nanoaggregates inducing and stabilizing the PMMA aggregates. PMMA/PEO interactions dependent of tacticity PMMA are responsible for these nanostructures. They are not only controlled by PMMA tacticity but also by concentration and molecular weight of PEO. In chloroform, an interaction model in three stages depending on PEO concentration has been deducted highlighting predominant effect of polymer conformation on these interactions. In addition, a generalization of this stereospecific interactions model in several solvents has highlighted the correlation between the length of isotactic or syndiotactic sequences, their conformations and PEO molecular weight. In a second step, we were able to deduce a correlation with the decrease of stereocomplexation phenomenon in the systems PMMA stereocomplex/PEO/CD3CN based on interactions observed between the two polymers in solution in acetonitrile. PEO partly disrupts stereocomplex formation, thus highlighting the influence of PEO presence on hollow PMMA nanocapsules structure and its disintegrating effect. These studies have shown that diffusion mechanisms through the walls used in controlled release systems cannot ignore preliminary analysis of potential interactions between probe molecules and polymer walls structure. Indeed, these interactions can significantly change the structure of these containers and delivery mechanisms must take these effects into account quantitatively to be efficient.These studies suggest scientific approach to follow the development of controlled release model of active molecules through nanocapsules membranes, which are included in polymeric systems.

Ce travail s'inscrit dans le cadre d'un projet soutenu par la Région wallonne et a été réalisé en collaboration entre les unités de Chimie Organique et Médicinale (CHOM), de Chimie Structurale et des Mécanismes Réactionnels (CSTR), et de Chimie et Physique des Hauts Polymères (POLY). Il concerne la modification des propriétés du polypropylène (PP) isotactique par mise en œuvre réactive, et plus particulièrement le contrôle de sa cristallinité par l'action d'un composé bromé (N-bromosuccinimide) en présence d'un initiateur de radicaux libres à haute température (entre 180 et 260°C). L'objectif principal de cette étude est de parvenir à identifier et à contrôler les modifications induites au sein des produits, ce qui implique une compréhension fine des mécanismes chimiques intervenant lors de la mise en œuvre réactive du PP. Ces connaissances permettraient en outre de substituer la N-bromosuccinimide (qui génère des sous-produits toxiques et polluants) par un autre additif en vue d'une meilleure valorisation du procédé et des produits. La stratégie repose sur une double approche, basée d'une part sur une étude des divers paramètres qui influencent la réaction sur polymère, et d'autre part sur la synthèse d'un composé modèle du PP : le 2,4,6,8,10-pentaméthylundécane (PMU). Par extrusion réactive du polymère, nous avons obtenu des PP à cristallinité contrôlée (PPCC ; de semi-cristallin à amorphe), dont certains présentent un caractère élastomère marqué. Des études effectuées principalement par analyse thermique et par résonance magnétique nucléaire ont permis de corréler ces propriétés macroscopiques à une microstructure à stéréoblocs isotactiques/atactiques (épimérisation des carbones tertiaires du PP), combinée à la présence de branchements longs (recombinaison de macroradicaux). Par ailleurs, nous avons mis en évidence les différents paramètres susceptibles d'influencer la réaction d'épimérisation du PP. Bien que les informations découlant de ces études nous aient permis de proposer les principaux mécanismes qui entrent en jeu lors de la réaction, seule une étude sur composé modèle peut néanmoins donner accès aux méthodes d'analyses nécessaires à la confirmation de ces mécanismes. Nous avons par conséquent entrepris la synthèse d'un oligomère de propylène pour permettre cette étude sur composé modèle. La synthèse du PMU telle que rapportée dans la littérature s'est avérée plus difficile que prévu, principalement du fait d'un manque de reproductibilité au niveau de l'étape clé. Nous avons donc établi une voie de synthèse originale permettant l'obtention du PMU (mélange de stéréoisomères) avec un rendement global de 45% sur 7 étapes (à l'échelle de plusieurs grammes de produit). En outre, cette voie nous a donné accès au 6-hydroxyméthyl-2,4,8,10-tétraméthylundécane et au 6-p-toluènesulfonyloxyméthyl-2,4,8,10-tétraméthylundécane, pour lesquels des techniques chromatographiques ont permi une séparation des diastéréoisomères. La transposition de ces expériences à plus grande échelle permettra d'envisager l'obtention du (4R,6s,8S)-PMU, en vue de futures études mécanistiques relatives à l'épimérisation du PP de configuration initialement isotactique. / This work is part of a project supported by the Walloon Region, and it was performed in collaboration between the Chimie Organique et Médicinale (CHOM), Chimie Structurale et des Mécanismes Réactionnels (CSTR), and Chimie et Physique des Hauts Polymères (POLY) laboratories. Its object is the modification of the isotactic polypropylene (PP) properties by reactive processing, and more especially the control of PP crystallinity by means of a brominated additive (N-bromosuccinimide) in presence of a free radical initiator at high temperatures (between 180 and 260°C). The main objective of this study is to identify and to control the modifications induced in the products, which implies a fine understanding of the chemical mechanisms occuring during the PP reactive processing. This knowledge would allow us, subsequently, to substitute another additive for the N-bromosuccinimide (which yields toxic and polluting by-products), in order to achieve a better applicability of both the process and the products. The strategy relies on a double approach : on one side, on a study of the various parameters affecting the reaction on the polymer, and on the other side on the synthesis of a model compound of PP : 2,4,6,8,10-pentamethylundecane (PMU). By means of reactive extrusion of the polymer, we obtained controlled crystallinity PP's (from semi-crystalline to amorphous), including some with an elastomeric behaviour. Studies carried out mainly by thermal analysis and nuclear magnetic resonance allowed us to correlate these macroscopic properties to an isotactic/atactic stereoblock microstructure (epimerization of the PP tertiary carbons), combined with the presence of long chain branchings (recombination of macroradicals). Moreover, we highlighted the various parameters that are able to influence the yield of the epimerization reaction. Even if the informations arising from these studies allowed us to propose the main mechanisms involved in the PP modification, only a mechanistic study carried out on a model compound would give us access to the characterization methods required for the confirmation of these mechanisms. We undertook, subsequently, the synthesis of a propene oligomer. The PMU synthesis, as stated in the litterature, revealed itself more difficult than initially foreseen, mainly due to a lack of reproducibility concerning the key step. Therefore we established a new synthesis pathway for the PMU (as a mixture of stereoisomers) with a global yield of 45% over 7 steps (multigram scale). Moreover, this pathway gave us access to 6-hydroxymethyl-2,4,8,10-tetramethylundecane and 6-p-toluenesulfonyloxymethyl-2,4,8,10-tetramethylundecane, for which chromatographic techniques allowed a separation of the diastereoisomers. The transposition of these experiments on a larger scale would allow us to obtain the (4R,6s,8S)-PMU for future mechanistic studies relative to the epimerization reaction of initially isotactic PP.

Le poly(acide lactique) (PLA), un polyester bio-ressourcé et biodégradable, est un candidat majeur pour la substitution des polymères issus de ressources fossiles. Le contrôle méticuleux de sa microstructure permet de modifier ses propriétés physiques. Dans ce contexte, ce manuscrit rapporte le design de complexes originaux de métaux trivalents et leur utilisation pour la polymérisation par ouverture de cycle (ROP) stéréosélective du lactide racémique (rac-LA). Ainsi, (i) les complexes M-Salen chiraux (M = Al, Ga, In, Salen = (1,2-diphényléthane)bis(phénoxyimine)) ont permis de confirmer l’aptitude des précatalyseurs aluminiques à être isosélectifs (Pm = 0.90) pour la ROP du rac-LA dénotant toutefois de leur faible activité. L’utilisation du gallium et de l’indium dans le but d’augmenter l’activité des systèmes catalytiques correspondants n’a pas permis de conserver la stéréosélectivité. Des études cinétiques et microstructurales ont permis d’établir les mécanismes de ROP et de stéréocontrôle ; (ii) les nouveaux ligands Salan rigidifiés par un cœur hydropyrimidine ((hydropyrimidine)bis(méthylène))diphénol), ont révélé une activation Csp3-H intramoléculaire inattendue avec le gallium et l’indium menant à des entités zwitterioniques originales. Les études mécanistiques par RMN, GC et calculs DFT ont permis de décrire le mécanisme alors mis en œuvre ; (iii) un précatalyseur hétéro-bimétallique yttrium/lithium et basé sur un ligand chiral dérivé de la binaphthylamine, a permis d’engendrer un PLA quasiment parfaitement hétérotactique (Pr = 0.99) ; (iv) finalement, de nouveaux ligands chiraux à base de proline pourront permettre de s’orienter vers l’utilisation de métaux divalents (Zn, SnII…), dans le but d’accéder à des systèmes stéréosélectifs faisant preuve d’une meilleure activité catalytique. / Poly(lactic acid) (PLA) is one of the most promising bio-resourced and biodegradable polymers and may constitute a viable alternative to petroleum-based materials. Its physical properties can be tuned by an accurate control of his microstructure. In this context, this manuscript relates the design of original complexes of trivalent metals and their further use for the stereoselective ring-opening polymerisation (ROP) of racemic lactide (rac-LA). Hence, (i) the chiral M-Salen complexes (M = Al, Ga, In, Salen = (1,2-diphenyl-ethane)bis(phenoxyimine)) have confirmed the isoselectivity exhibited by aluminium precatalysts for the ROP of rac-LA (Pm = 0.90) but also their limited activity. The gallium and indium congeners were prepared to enhance the catalytic activity, but resulted on substantial loss of stereoselectivity. The ROP and stereocontrol mechanisms were both investigated by kinetic monitoring and by microstructural analysis of the polymer; (ii) novel Salan ligands rigidified by a hydropyrimidine core ((hydropyrimidine)bis(methylene))-diphenol) have led to unexpected intramolecular Csp3–H activation with gallium and indium, affording unusual zwitterionic complexes. NMR and GC studies as DFT computations have been implemented to understand the mechanism for this process; (iii) a hetero-bimetallic yttrium/lithium precatalysts based on a chiral binaphthylamine backbone has led to highly heterotactic PLA (Pr = 0.99); (iv) finally, new chiral ligands should afford complexes of divalent metals (Zn, SnII…) that should yield access to stereoselective catalytic systems featuring increased activity.