1,135 research outputs found
The synthesis and properties of some well-defined fluorinated polymers
No full textThis thesis describes studies directed to the ring opening metathesis polymerisation (ROMP) of some fluorinated compounds using a range of well-defined initiators. Chapter 1 reviews some general aspects of olefin metathesis and ring opening metathesis polymerisation of relevance to the work described in this thesis. Topics such as piezo- and pyro-electricity and optical and electrical properties of conjugated polymers are introduced and these receive more detailed attention later in the thesis. Chapter 2 describes the synthesis, characterisation and properties of . poly(bis(trifluororaethyl)norbomadiene) in detail. The use of various initiating systems that have been used previously and the effect they have on the tacticity of the resulting polymer raicrostructure are discussed. The latter part of this chapter reviews some of the current thinking concerning the detailed mechanistic aspects of this polymerisation. Chapter 3 reviews attempts directed to an improvement in tacticity control in the synthesis of poly(bis(trifluoromethyl)norbomadiene). The synthesis and activity of the new well-defined initiators used in these studies are reported. It is shown that varying the nature of the ancillary Ligands surrounding the metal centre can have a dramatic influence on the tacticity of the resulting polymer. Chapter 4 reports studies directed to an examination of the limits of the well controlled synthesis of poly(bis(trifluoromethyl)norbornadiene). The syntheses of high trans and high cis, highly tactic poly(bis(trifluoromethyl)norbornadiene samples using well-defined initiating systems are described. It is shown that by varying the monomerinitiator ratio, samples with a wide range of molecular weights can be achieved and these are reported. Chapter 5 describes experiments concerning the ROMP of fluorinated monomers containing six membered rings. In particular ROMP studies of the monomers, 2,3-bis(trifluoromethyl)bicyclo[2.2.2]octa-2,5-diene . and 2,3- (tetrafluorobenzo)bicyclo[2.2.2]octatriene are described finally, Chapter 6 provides a summary of the work reported and outlines some ideas for future studies
Thin aligned organic polymer films for liquid crystal devices
No full textThis project was designed to investigate the possibility of producing alignment layers for liquid crystal devices by cross-linking thin films containing anisotropic polymer bound chromophores via irradiation with polarised ultra violet light. Photocross-linkable polymers find use in microelectronics, liquid crystal displays, printing and UV curable lacquers and inks; so there is an increasing incentive for the development of new varieties of photopolymers in general. The synthesis and characterisation of two new photopolymers that are suitable as potential alignment layers for liquid crystal devices are reported in this thesis. The first polymer contains the anthracene chromophore attached via a spacer unit to a methacrylate backbone and the second used a similarly attached aryl azide group. Copolymers of the new monomers with methyl methacrylate were investigated to establish reactivity ratios in order to understand composition drift during polymerisation
Electroactive polymers from β-substituted thiophenes
No full textThe work reported in this thesis can be broken down into three main areas. The first describes the synthesis of a series of β-substituted thiophenes bearing long, lipophilic chains (either ether, polyether or amido in nature). Cyclic voltammetry studies on the monomers revealed their oxidation potential but did not prove to be a successful method of electropolymerisation. This was achieved using constant current electrolysis and further studies involving FTIR, ESCA and SEM were carried out on the most highly conducting polymer. This polymer was also solution processible in its conducting form. The second area also describes the synthesis of a series of β-substituted thiophenes, but this time the pendant side group consists of bulky phenoxy moieties (liquid crystals, phenol ethers and aminophenol ethers). In this case the cyclic voltammetry studies carried out did appear to provide a successful means of generating polymers. Finally, the synthesis of a series of β-substituted thiophenes bearing pendant macrocyclic substituents (an N-0-5 cycle, an oxo-cyclam and a 14-0-4 cycle) are described. Their cyclic voltammetry behaviour is reported in detail and the results of experiments to determine metal ion selectivity is also described, in the case of the 14-0-4 cycle
Synthesis and cell adhesion studies of linear and hyperbranched poly(butyl methacrylate) and poly(t-butyl acrylate)
No full textA library of polymers/oligomers with three different architectures was synthesised. Short chain, linear oligomers were produced by performing oxidative cleavage on a poly(butyl methacrylate-co-butadiene) polymer. Although butadiene is a gaseous monomer, it was found that careful control over the reaction conditions led to successful copolymerisation in an unpressurised reactor. Hyperbranched polymers of n-butyl methacrylate and t-butyl acrylate
were synthesised by RAFT polymerisation with 4-vinylbenzyl-pyrrolecarbodithioate (CTA1) and 4-vinylbenzyl dithiobenzoate (CTA2). A variety of analytical techniques, such as elemental analysis and NMR, were used to characterise the polymers and confirm the hyperbranched structure. Some variation in monomer conversion and CTA uptake was seen under different polymerisation conditions.
After synthesis and characterisation, it was found that the polymer end groups could be modified through work up with diamine or 4.4‘-azobiscyanovaleric acid. Linear oligomers of
butyl methacrylate were functionalised with amines whilst hyperbranched polymers were given acid functional end groups. FT-IR and elemental analysis were used to monitor the success of the end group reactions. As the polymers could be applied as films, they were assessed as cell culture substrates using Human dermal fibroblasts (HDF) and Human renal epithelial cells (HREp). A linear butyl
methacrylate-co-4-vinyl benzoic acid copolymer was also assessed in comparison to the hyperbranched structures. It was observed that the two cell types had different responses to each of the polymers. Fibroblast cells showed better rates of adhesion and proliferation on
acid-functionalised polymers, whilst epithelial cells performed best on the aminefunctionalised moieties.
This work provides useful information for the synthesis and preparation of new biomaterials. It has been found that polymer functionality must be considered when compatibility with a specific cell type is desired, and polymers with the potential to be incorporated into future biomaterials are highlighted
Síntese de materiais poliméricos assistida por ultrassom
No full textDissertação (mestrado) - Universidade Federal de Santa Catarina, Centro Tecnológico, Programa de Pós-Graduação em Engenharia Química. Florianópolis, 2014.No presente trabalho avaliou-se a síntese de diferentes polímeros como poli(adipato de isosorbila), poli(metracrilato de metila) e poli(uréia-uretano) em banho termostático convencional e em banho de ultrassom. Os polímeros foram sintetizados via diferentes técnicas de polimerização como polimerização em massa, miniemulsão e solução, seguindo diferentes mecanismos de reação: em cadeia, etapas e em etapas catalisada por enzimas. Adicionalmente foi avaliado o efeito de diferentes potências do banho de ultrassom (52,8; 92,5 e 132 watts) na síntese dos polímeros. Na polimerização do isosorbídeo e do adipato de dietila em massa e em miniemulsão verificou-se que o banho de ultrassom não afetou a cinética reacional quando comparada com as reações em banho convencional e na polimerização em solução as massas molares apresentaram um leve aumento para as condições de 85°C com 92,5 W e 85°C e 132 W de potência, respectivamente, utilizando um sistema ciclohexano:benzeno como solventes. O mesmo comportamento foi observado na síntese do poli(metracrilato de metila) em massa e em miniemulsão com o uso do banho de ultrassom, sendo que o uso deste não afetou a velocidade de reação e ocasionou uma ligeira redução nas massas molares do poli(metracrilato de metila) obtido via miniemulsão em banho de ultrassom a 132 W de potência. Os estudos para a obtenção de nanopartículas de poli(uréia-uretano) via polimerização em miniemulsão em banho termostático e em banho de ultrassom revelaram que diferentes temperaturas de reação na faixa entre 60°C e 80°C no banho de ultrassom influenciaram diretamente nas massas molares dos polímeros e no aumento da taxa de reação do monômero, enquanto que a variação da potência máxima do ultrassom na faixa estudada (92,5 a 132 W) alterou a taxa de reação, mas não afetou as massas molares, sendo alcançadas massas molares ponderais médias em torno de 20000 g/mol nas reações realizadas a 70°C em banho de ultrassom.Abstract: This work presents the synthesis of various polymeric materials such as poly(isosorbide adipate), poly(methyl methacrylate) and poly(urea-urethane) in conventional thermostatic and ultrasound bath. The polymers were synthesized by bulk, solution and miniemulsion polymerizations, following different reaction mechanisms: chain polymerization, step polymerization and enzimatically catalized step polymerization. Aditionally the effect of power of the ultrasound bath (52.8, 92.5 and 132 watts) was evaluated. In the polymerization of the poly (isosorbide adipate) in mass and in solution it was found that the ultrasound bath does not affect the reaction kinetics when compared with conventional bath. In the solution polymerization, the molar mass increased slightly for the conditions of 85°C at 92.5W and 85°C at 132 W power, respectively, using a ciclohexane:benzene system as solvent. The same behavior was observed in the synthesis of poly (methyl methacrylate) in mass and miniemulsion using the ultrasound bath, and the use of the latter does not affect the reaction kinetics, but lead to a slight reduction in the molecular weight of poly(methyl methacrylate) obtained in miniemulsion via ultrasound bath at 132 W of power. Studies for obtaining nanoparticles of poly(urea-urethane) by miniemulsion polymerization with thermostatic bath, and ultrasound bath revealed that different reaction temperatures in the range between 60°C and 80°C in the ultrasound bath directly influence the molar mass of the polymers and increase the reaction rate of the monomer, while the variation of the maximum power of the ultrasound in the studied range (92.5 to 132 W) affected the reaction rate but did not influence the molar mass. The weight awerage molar mass was around 20000 g/mol for reactions conducted at 70°C in the ultrasound bath
The Water Uptake of Experimental Soft Lining Materials
No full textPhDIn order to develop a successful soft lining material various factors have to be
considered; physical strength, adhesion to the denture base ( or prosthetic) and the
durability of the material's properties when in the mouth. It has been recognised that in
order to fulfil these criteria the material must be stable and have a low water uptake from
the aqueous environments of the mouth.
In the dental field comparatively little work has focused on how soft lining materials
behave in water where as water in polymers has received a considerable amount of
interest, with many different types of behaviour being observed and explained. It has
been realised by previous authors that the water uptake of elastomers is primarily driven
by soluble impurities, these form solution droplets within the material. The nature of the
growth is somewhat more debatable, with both Fickian and dual sorption kinetics being
reported.
Two basic types of materials were used in the study; silicone polymers and elastomer /
methacrylate materials. Silicone polymers are characterised by a low water uptake and
form the basis of perhaps the most successful soft lining material ('Molloplast B'). The
elastomer / methacrylate materials were based on those developed by Parker (1982),
Parker and Braden (1990) which showed considerable promise but suffered from an
extensive protracted uptake. Water uptake at 370C in conjunction with the tensile
strength were used to evaluate the materials produced as these simple tests enabled the
behaviour of the material in service to estimated.
Three different types of silicone polymers were used during the study classified by the
curing mechanism (condensation, peroxide and hydrosilanised), various fillers and
additives (such as calcium stearate) were incorporated into the materials and different
uptakes observed. The condensation silicones demonstrated large weight losses (up to
20 wt%) in water which is attributed to hydrolytic instability of the siloxane bridge in the
presence of an organo tin compound leading to a leaching of siloxane. The pure
peroxide and hydrosilanised materials both demonstrated a low water uptake but when
doped they form solution droplets in a similar way to that described in the literature.
Other additives showed different behaviour with the formation of cracks within the
silicone due to failure of the material around the droplets, the action of hydrophilic but
insoluble fillers also promotes the uptake. The hydrosilanised silicone polymers showed
considerable promise as soft lining materials with low water uptake and good tensile
strength.
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The elastomer / methacrylate materials were based initially on butadiene styrene
copolymer and a higher methacrylate monomer which formed a gel this was then free
radically cured. The water uptake of these materials was attributed to soluble separating
agent added to the butadiene styrene (to prevent particle agglomeration) during the
production of the powdered elastomer. The extent of the uptake could be controlled by
improving the strength of the material but the overall uptake remained too high. When
the material was placed in an osmotic solution (Na CI or glucose) the water uptake was
significantly reduced and the behaviour could be described by a modified (for small
strains) version of the Thomas and Muniandy (1987) theory for the growth of water
droplets in a elastomer.
In order to reduce the water uptake of the elastomer / methacrylate materials butadiene
styrene copolymers without separating agent was used. The emulsion polymerised
material contained soluble impurities from the polymerisation (i.e. soap)which acted to
drive the water uptake. Solution polymerised butadiene styrene also demonstrated a high
uptake but this is attributed to a clustering behaviour of carboxylic and hydroxyl groups
which formed post production. Similar behaviour is also seen for a solution polymerised
isoprene styrene elastomer. The role of crosslinking the material in restraining the
growth of the droplets is also investigated with dramatic reductions in the uptake being
observed as the crosslink density increased. The employment of a reinforcing silica filler
proved more effective than simply using a dimethacrylate. Oxidation is another problem
(characterised by an upturn in the absorption), although not observed in every case it was
a problem for all of the unsaturated elastomers and was found to be promoted by ions
present within saliva. Saturated butyl based (including chloro and bromo butyl)
elastomers were used instead and did not show any tendency for oxidation but they still
showed an uptake of approximately 3 to 4 wt%. Their stability however and reasonable
strength makes them suitable for further development as soft lining materials.
Theoretical considerations were investigated by HI NMR imaging with the formation of
droplets being observed, the profiles seen indicating the absorption to be two stage
rather than Fickian. The role of creep or stress relaxation is also identified as a
mechanism for extending the uptake by reducing the restraining force. Further reasoning
on all the data presented here concluded the role of chemical potential change associated
with the water into the matrix or the droplets will determine the nature of the uptake
observed
One‐Pot Structure‐Controlled Synthesis of Hyperbranched Polymers by a “Latent” Inimer Strategy Based on Diels–Alder Chemistry
No full textAn efficient “one-pot” strategy for the structure-controlled synthesis of hyperbranched polymers (HBPs) based on a "latent" inimer (LI-Br), containing a furan-protected maleimide monomer and a haloalkane initiator, is presented. At high temperatures, the "latent" inimer is converted to a "real" inimer after releasing maleimide (MI) via a retro-Diels-Alder (r-DA) reaction and then copolymerized with methyl methacrylate by self-condensing vinyl copolymerization. Due to the dynamic characteristic of the r-DA reaction, the release of naked MI and the subsequent copolymerization can be regulated by the temperature or stereochemistry of Diels-Alder (DA) adducts. Thus, the “one-pot” structure-controlled synthesis of HBPs with various degrees of branching was achieved. By further implementation of a programmable temperature change, some valuable hyperbranched topologies such as star-shaped and long-chain hyperbranched polymers can be constructed avoiding sophisticated synthetic routes.We gratefully acknowledge financial support from the National Natural Science Foundation of China (52103016, 51873233), Innovation Group of National Ethnic Affairs Commission of China (MZR20006), and the South-Central Minzu University (YZZ19002). N.H. acknowledges the support of KAUST
The surface chemistry of polymeric bioseparation materials
No full textThe aim of this thesis was to test existing theories concerning biocompatibility of polymeric materials, and in the process to try and identify the major factors which pertain to their use as bioseparation matrices. The surface chemistry of cellulose and poly(tetrafluoroethyIene) based bioseparation materials have been examined. We have been able to demonstrate a direct link in the case of the cellulose materials between the crystallinity and the accessibility of the hydroxyl groups which are the primary sites of functionalization. In addition, the effect of processing conditions on the pore structure of an amorphous cellulose matrix was demonstrated and this has been shown to have a direct consequence for the protein binding characteristics of the material. The functionalisation of PTFE has been achieved by reaction with sodium naphthalenide, which lead to the defluorination of the PTFE surface and the formation of a unsaturated carbonised layer containing oxygenated functionalities. The reaction has also been shown to alter the morphology of PTFE membranes as evidenced by AFM analysis. In the case of powdered PTFE we observed the formation of a microporous layer, however this was found to revert back to a fluorinated layer with gentle heating. A novel insight in to the defluorination reaction was obtained using the bombardment of PTFE and PVDF with a Na atom beam under ultra-high vacuum conditions. This demonstrated the single valence electron mechanism of the reaction and also showed the formation of NaF at the surface of the polymer. The formation of CF(_3) groups was attributed to the nucleophilic attack of fluoride ions from molecular NaF species formed at the initial stages of the reaction
Desenvolvimento de polímeros híbridos orgânico-inorgânicos para aplicação como revestimentos protetores
No full textTese (doutorado) - Universidade Federal de Santa Catarina, Centro Tecnológico, Programa de Pós-Graduação em Engenharia Química, Florianópolis, 2014.O PMMA é um polímero orgânico muito utilizado na formulação de revestimentos e adesivos devido à boa adesão em diversos substratos e à facilidade em produzir recobrimentos poliméricos. Por outro lado, o PMMA é hidrofílico, possui baixa resistência térmica e baixa resistência aos fenômenos de corrosão. Uma forma adequada de melhorar as propriedades desse material é através da combinação com compostos inorgânicos, formando polímeros híbridos orgânico-inorgânicos. Neste contexto, foram desenvolvidos polímeros híbridos de PMMA/polissilazano com o objetivo de melhorar as propriedades do componente orgânico visando aplicação como revestimento protetor. Todavia, o oligossilazano selecionado neste trabalho, HTT1800, quando em contato com a umidade e oxigênio, forma reticulações que produzem um polímero termofixo e insolúvel, impossibilitando a aplicação como revestimento. Sendo assim, a polimerização em solução com atmosfera de argônio foi a técnica selecionada para a síntese dos materiais híbridos, pois impede o contato dos componentes de partida com ar e umidade. Os polímeros e os revestimentos híbridos desenvolvidos foram caracterizados para avaliar a influência do HTT1800 nas propriedades finais desses materiais em relação ao PMMA puro. A partir dos resultados da extração soxhlet, observou-se que os polímeros híbridos sintetizados com até 25% em massa de HTT1800 apresentaram baixo grau de reticulação e, por isso, deram origem a soluções poliméricas adequadas para deposição nos substratos metálicos. Adicionalmente, as curvas de TGA e DTA evidenciaram que a inclusão do HTT1800 aumentou a estabilidade térmica do PMMA e, a partir dos resultados de GPC, observou-se a diminuição das massas molares dos materiais híbridos em relação ao PMMA puro. Além disso, o oligossilazano melhorou a adesão dos revestimentos no substrato metálico e conferiu hidrofobicidade aos revestimentos produzidos. Os testes de corrosão comprovaram a eficiência de proteção dos revestimentos híbridos em comparação com o substrato sem revestimento e com o PMMA puro. Desta forma, o desenvolvimento dos polímeros híbridos orgânico-inorgânicos de PMMA/HTT1800 permitiu a obtenção de revestimentos protetores com propriedades superiores às observadas em revestimentos de PMMA puro.PMMA is an organic polymer that has increasingly been used as coatings and adhesives due to its good adhesion in different types of substrates and excellent film-forming performance. However, PMMA is hydrophilic and shows low thermal and corrosion resistance. A suitable way to enhance the properties of this material is the combination with inorganic compounds to form organic-inorganic hybrid polymers. In this work, hybrid polymers of PMMA/polysilazane were synthesized aiming the improvement of the organic component properties for application as protective coatings. However, the selected oligosilazane, HTT1800, is a very reactive compound, which undergoes cross-linking if in contact with water and/or oxygen. The cross-linking leads to a thermoset and insoluble polymer and hinders the application as coating. Therefore, the solution polymerization in argon atmosphere was the chosen technique for the synthesis, preventing the contact with air and humidity. Different characterizations were carried out to evaluate the influence of the HTT1800 in the final properties of the developed hybrid polymers and of the coatings in comparison to the pure PMMA. Soxhlet extraction results showed that a low cross-linking degree is obtained when HTT1800 content in the initial mixture do not exceed 25 wt%, producing polymeric solutions with adequate characteristics for the formation of hybrid films on the metal substrate. Additionally, TG and DTA analyses indicated that the addition of HTT1800 increased the thermal stability of the PMMA and the GPC analysis results showed a decrease of the hybrid polymer´s molecular weight in comparison to the pure PMMA. Furthermore, the oligosilazane improved the adhesion of the coatings on the metal substrate and the hydrophobicity of the developed films. The corrosion tests showed that the hybrid coatings had better anticorrosive performance in comparison to the uncoated substrate and to the pure PMMA. Thus, the development of organic-inorganic hybrid polymers of PMMA/HTT1800 enabled the production of protective coatings with enhanced properties if compared to pure PMMA
POLYMER MODIFIED ASPHALT NANOCOMPOSITES
No full textAsphalt one of the versatile materials of antique, inspite of its compositional
variations and complexities, widely employed in various applications like water
proofing, paving etc. Due to the complex physical and chemical nature, Asphalt
seldom performs well, without any modification. Amidst other materials, polymers
found to be most suitable for modifying asphalt to suit the application demands.
Nanomaterials, particularly invention of nanoclays, have enhanced the properties
of polymers manifold when introduced in polymer. Polymer Nanocomposites thus
obtained emerge with innovative properties which are not available with existing
polymers. Similar to the effect of nanoclay in polymer, polymers improve the
properties of asphalt. The hypothesis behind this work is to combine the
advantages of nanoclay in polymer and polymer in asphalt by introducing, polymer
and nanoclay in asphalt. Two different nanoclays, Cloisite 20A and Dellite 43B,
were introduced along with EVA by different methods such as Physical Mixing and
Melt Blending. This gave rise to Polymer Modified Asphalt Nanocomposites
(PMAN) a new class of material. Thermal, morphological, structural and
rheological properties were studied. Based on the above studies, fuel resistance
PMAN with EMA, EVA and SBS developed. Also, flammability of PMAN was
studied by developing new test method using Limiting Oxygen Index equipment.
From this research work, new class of materials (PMAN) based on polymer and
nanoclay with improved rheological and performance properties, fuel resistance
were developed
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