Academic literature on the topic 'Polymer backbone'

xxii, 143 p. ; ill. (some col.) A print copy of this title is available through the UO Libraries. Search the library catalog for the location and call number.<br>There are compelling economic and environmental reasons for using degradable plastics in selected applications and considerable research is now devoted to devising new photodegradable polymers with improved performance. Controlling the degradation of these materials in a prescribed fashion is still a difficult problem because the parameters that influence degradation rates are not completely understood. In order to predict polymer lifetimes, to manipulate when a polymer starts to degrade, and to control the rate of degradation, it is necessary to identify the experimental parameters that affect polymer degradation rates and to understand how these parameters affect degradation. This dissertation describes the results of experiments designed to gain fundamental insight into the factors that affect the rate of polymer photodegradation. The key experimental strategy employed was the incorporation of organometallic dimers into the backbone of the polymer chains, specifically, [CpRMo(CO) 3 ] 2 (CpR = a substituted cyclopentadienyl (· 5 -C 5 H 4 R)). Incorporating these organometallic units into a polymer chain make the polymer photodegradable because the metal-metal bond can be cleaved with visible light. The photogenerated metal radicals can then be trapped by O 2 or chlorine, resulting in degradation of the polymer. Another benefit from incorporating this chromophore into the polymer backbone is that it provides the experimentalist with a convenient spectroscopic handle to monitor degradation rates. Using these model polymers, several experimental factors that can affect polymer photodegradation rates have been explored. For example, experiments showed that radical trap concentration affects degradation rates below, but not above, the polymer glass transition temperature. In addition, degradation rates as a function of irradiation temperature, tensile stress, and time-dependent morphology changes were explored for various polymers. The results of these studies suggest that the ability of the photogenerated radicals to escape the radical cage is the dominant factor in determining photodegradation efficiencies. This dissertation includes previously published and unpublished co-authored material.<br>Adviser: David R. Tyler

Una delle principali applicazioni in cui i polimeri elastomerici trovano impiego è come componente strutturale nella formulazione di mescole per pneumatici. Tuttavia, affinché il prodotto finale possa soddisfare gli standard di prestazione richiesti, è necessario introdurre nella matrice polimerica dei componenti (filler) inorganici (Silice e Carbon Black). Sotto questo profilo, la compatibilità tra la fase polimerica e inorganica è dunque un aspetto di cruciale importanza. In questo contesto si colloca il presente progetto di dottorato, che ha come obiettivo quello di sviluppare un’innovativa strategia per migliorare il composito finale attraverso l’introduzione di gruppi funzionali sulla matrice polimerica in grado di interagire con le componenti inorganiche presenti in una mescola. Come prima cosa sono state scandagliate le opportunità che la letteratura offriva per trovare una reattività in grado di interessare i legami insaturi presenti nella matrice polimerica. In particolare, sono state identificate tre possibili alternative:cicloaddizione 1,3-dipolare, reazioni di tipo Tiol-Ene e reazioni di tipo Alder-Ene. Dopo aver verificato pregi e difetti di ciascuna reattività, la più promettente si è rivelata essere quella basata su una reazione di tipo Alder-Ene, che prevede l’interazione tra un’olefina, recante idrogeni in posizione allilica, ed un enofilo elettron-povero. Il composto enofilo da noi utilizzato e studiato come sistema modello è stato il 4-phenyl-1,2,4-triazoline-3,5-dione (PhTAD). Questo sistema, una volta ancorato sul polimero, presenta un gruppo ammidico secondario libero, in grado di modificare localmente la polarità della matrice e, contemporaneamente, di interagire tramite legami ad idrogeno con i filler inorganici come la silice. L’attività di ricerca è stata dunque concentrata sulla modifica chimica, con PhTAD, di olefine commerciali. Tali polimeri modificati, con diverse quantità di funzionalizzante, sono stati quindi caratterizzati tramite un approccio multitecnica (DSC, TGA, FTIR e prove di swelling) ed in seguito introdotti in mescola. Le proprietà reologiche delle mescole ottenute sono state valutate sia con un reometro a disco oscillante (ODR) sia tramite analisi dinamico meccaniche a temperatura variabile (DMTA) ed analizzandone le curve di stress-strain. Si è quindi tentato di risolvere le criticità emerse nell’utilizzo di PhTAD come agente di funzionalizzazione. Innanzitutto, è stato necessario ottimizzarne la quantità introdotta in mescola arrivando, nel migliore dei casi, ad ottenere compositi in cui i valori di G’ fossero comparabili con gli standard di rifermento industriali, che si basano sull’utilizzo di agenti compatibilizzanti come il TESPT, con un contestuale leggero peggioramento dei valori come il tanδ o l’effetto Payne, indice di un’effettiva interazione tra la matrice polimerica funzionalizzata con le cariche di silice, seppur non ottimale. Inoltre, uno dei maggiori problemi intrinseci da risolvere nell’utilizzo di una molecola come il PhTAD, risiede nella sua alta reattività che rende impossibile operare in massa, direttamente sul polimero pristino. L’ultima parte del progetto è stata quindi dedicata alla sintesi di funzionalizzanti di natura simile, a base diazenica, ma meno reattivi, allo scopo di far avvenire la reazione sul polimero direttamente in fase di formulazione, alle temperature a cui vengono processate le mescole (≈140°C), svincolandosi così dalla difficoltà derivanti dell’operare in soluzione. In particolare,l’avvenuta funzionalizzazione di un sistema oligomerico modello con ethyl(anilinocarbonyl)diazenecarboxylate ha permesso di dimostrare la validità dell’idea di una funzionalizzazione in massa termicamente stimolata, aprendo alla possibilità di impiego di altri sistemi molecolari, modificabili appositamente per assolvere una funzione specifica all’interno della mescola.<br>One of the main applications in which elastomeric polymers are used is as a structural component in the formulation of tire compounds. However, to match the required performance standards for the final product, it is necessary to introduce inorganic components (fillers) (Silica and Carbon Black) into the polymer matrix. From this point of view, the compatibility between the polymeric and inorganic phases is, therefore, an aspect of crucial importance. In this context the present PhD project is set up, which aims to develop an innovative strategy to improve the final composite through the introduction of functional groups on the polymer matrix able to interact with the inorganic components present in a compound. First, the opportunities offered by the literature to find a reactivity able to affect the unsaturated bonds present in the polymer matrix were explored. In particular, three possible alternatives have been identified: 1) 1,3-dipolar cycloaddition 2) Tiol-Ene type reactions 3) Alder-Ene type reactions After having verified the strengths and weaknesses of each reactivity, the most promising one has been to be based on an Alder-Ene reaction, which involves the interaction between an olefin (bearing hydrogen in an allyl position) and an electron-poor enophile. The enophilic compound we studied as a model system was 4-phenyl-1,2,4-triazoline-3,5-dione (PhTAD). This system, once anchored on the polymer, has a secondary amide group, able to modify locally the polarity of the matrix and, at the same time, able to interact through hydrogen bonds with inorganic fillers such as silica. The research activity has been focused on the chemical modification, with PhTAD, of commercial unsaturated polymers. These modified polymers, with different amounts of functionalizer, were then characterized by a multitechnical approach (DSC, TGA, FT-IR and swelling tests) and subsequently introduced into the mixture. The rheological properties of the compounds obtained were evaluated both with an oscillating disk rheometer (ODR), and by dynamic mechanical analysis at variable temperatures (DMTA) and by analyzing stress-strain curves. Preliminary attempts have been performed to resolve the critical issues that emerged when using PhTAD as a functionalization agent. First, it was necessary to optimize the amount introduced into the mixture, arriving, at best, to obtain composites in which the values of the G' module were comparable with the industrial reference standards, which are based on the use of compatibilizing agents such as TESPT, with a slight contextual deterioration of the values such as tanδ or the Payne effect, indicating an effective interaction between the polymer matrix functionalized with silica fillers, even if not yet optimally. Moreover, one of the major intrinsic problems to be solved in the use of a molecule such as PhTAD lies in its high reactivity which makes it impossible to operate in bulk, directly on the pristine polymer. The last part of the project was then dedicated to the synthesis of functionalizers of a similar nature, based on diazenics, but less reactive, in order to make the reaction occur on the polymer directly in the formulation phase, at the temperatures normally used to process compounds (≈140 °C), thus avoiding the difficulty due to operating in solution. The successful functionalization of a model oligomeric system with ethyl (anilinocarbonyl) diazenecarboxylate has allowed to demonstrate the validity of the idea of a thermally stimulated mass functionalization, opening to the possibility of using other molecular systems, that can be tuned specifically to perform a specific function within the compound.

There are two general ways to introduce functionalities into a polymeric structure: functionalization of the monomeric units before polymerization and postfunctionalization of the preformed polymer. Building libraries of polymers with different functionalities can be completed with significantly less effort by the second method, as each postfunctionalization of a single batch of polymeric backbone can involve as little as one synthetic step. One method of building a polymeric backbone for postfunctionalization involves the synthesis of hyperbranched conjugated polymers (HCPs) from AB2 monomeric units. A polymer formed from n AB2 monomeric units should contain n reactive B groups, which act as sites of functionalization. Utilizing this principle, two different hyperbranched poly(phenylene vinylene-phenylene ethynylene) scaffolds were synthesized and studied in both their inherent properties and functionalization. The first HCP synthesized was compared against a monomeric cruciform model and a linear polymer with a similar structure. The hyperbranched polymer has red-shifted absorption and emission in comparison to the cruciform model and linear polymer. The HCP quenches paraquat more efficiently than the linear polymer by a factor of about two, suggesting a greater rate of energy transfer. The functionalization of HCPs was studied; iodine groups decorating the HCPs were replaced with terminal alkynes by Pd-catalyzed coupling, providing a library of 24 differently functionalized HCPs. Elemental analyses of the postfunctionalized polymers show nearly complete substitution of the iodine groups. The postfunctionalized polymers show increased fluorescence compared to the original iodine decorated polymers, due to the loss of the heavy atom effect inducing iodine groups. The emissions of the postfunctionalized polymers in solution show a strong dependence on the groups attached to the conjugated structures, with emission maxima ranging from 505 nm to 602 nm; quantum yields range from 0.7% to 25%. Solid-state emission studies show stronger and more red-shifted spectra compared to emissions observed in solution.

Thesis (Ph. D.)--Southern Illinois University Carbondale, 2007.<br>"Department of Chemistry and Biochemistry." Keywords: Polysilane, Silicon backbone polymers, PC-12 cell growth, Nerve cell growth, Fibronectin, Polymers, Nerve growth substrates. Includes bibliographical references (p. 131-142). Also available online.

Polycarbynes ( poly(hydridocarbyne), poly(methylcarbyne) and poly(phenylcarbyne) ) are a class of network polymers which are primarily composed of tetrahedrally hybridizated carbon atoms which have hydrogen, methyl or phenyl pendant group linked via three carbon-carbon single bonds to form a three dimensional network of fixed rings. This backbone oers unusual properties on the polymer including thermal decomposition to form diamond and diamondlike carbon. In this thesis, polycarbynes were synthesized by electrolytical reduction of trihaloorganocompounds, namely chloroform, hexachloroethane, 1,1,1-trichloroethane and 1,1,1-trichlorotoluene. Poly(hydridocarbyne) was synthesized using chloroform and hexachloroethane. Poly(methylcarbyne) was synthesized from 1,1,1-trichloroethane. Poly(phenylcarbyne) was synthesized from 1,1,1-trichlorotoluene. Polycarbynes were characterized by UV/Vis spectroscopy, 1H and 13C NMR spectroscopy, FTIR and GPC. All results are found to be consistent with literature<br>and thus a single step cheap, safe and easy method was introduced to scientists and manufacturers in diamond science. The resulting polymers were heated upon 1000oC under nitrogen atmosphere for 24 hours yielding in the formation of diamond and diamond-like carbon. Results indicated that both diamond films and powders were successfully produced from polycarbynes. Diamonds formed from the polymers were characterized via optical microscope, SEM, X-ray and Raman spectroscopy. All results shown in thesis are completely consistent with studies previously done for polycarbynes and diamond.

Click chemistry is one of the growing areas of research which is applied in the design and synthesis of a wide range of polymeric architectures. This investigation focuses on the synthesis of fluorescent coumarin based polymers by “click” A-B step growth polymerization process and evaluation of their photophysical properties. Non-fluorescent azide-alkyne functionalized coumarin-based monomers were synthesized in multiple steps from 2,4-dihydroxybenzaldehyde in reasonable yields. Polymers with coumarin backbone were synthesized from azide-alkyne functionalized coumarin monomers via the Cu(I) catalyzed 1,3-dipolar cycloaddition reaction between azides and alkynes, a typical click reaction, to form polymers whose repeating units are connected by a 1,2,3-triazole ring. The structures of the synthesized polymers were confirmed by NMR and FT-IR spectroscopy. Finally, the photophysical properties of the synthesized monomers and polymers were evaluated in DMF. All coumarin based monomers showed reduced fluorescent properties due to the quenching effect from the azido group. Although all polymers absorbed at maximum wavelength of 340 nm, a characteristic for coumarin chromophore, the homo-polymers emitted at a shorter wavelength of 413 nm as compared to the co-polymers which emitted at 421 nm.