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Mechanistic studies of unusual Miruta-Baylis-Hillman reactionsNyoni, Dubekile January 2012 (has links)
This study has focussed on the application of synthetic, kinetic and exploratory theoretical methods in elucidating the reaction mechanisms of four Morita-Baylis-Hillman (MBH) type reactions, viz, i) the reactions of the disulfide 2,2'-dithiodibenzaldehyde with various activated alkenes in the presence of DBU and Ph₃P, ii) the reactions of chromone-3-carbaldehydes with MVK, iii) the reactions of chromone-2-carbaldehydes with acrylonitrile and iv) with methyl acrylate. Attention has also been given to the origin of the observed regioselectivity in Michaelis-Arbuzov reactions of 3-(halomethyl)coumarins. Cleavage of the sulfur-sulfur bond of aryl and heteroaryl disulfides by the nitrogen nucleophile DBU has been demonstrated, and a dramatic increase in the rate of tandem MBH and disulfide cleavage reactions of 2,2'-dithiodibenzaldehyde with the activated alkenes, MVK, EVK, acrylonitrile, methyl acrylate and tert-butyl acrylate has been achieved through the use of the dual organo-catalyst system, DBU-Ph₃P – an improvement accompanied by an increase in the yields of the isolated products. Detailed NMR-based kinetic studies have been conducted on the DBU-catalysed reactions of 2,2'-dithiodibenzaldehyde with MVK and methyl acrylate, and a theoretical kinetic model has been developed and complementary computational studies using Gaussian 03, at the DFT-B3LYP/6-31G(d) level of theory have provided valuable insights into the mechanism of these complex transformations. Reactions of chromone-3-carbaldehydes with MVK to afford chromone dimers and tricyclic products have been repeated, and a novel, intermediate MBH adduct has been isolated. The mechanisms of the competing pathways have been elucidated by DFT calculations and the development of a detailed theoretical kinetic model has ensued. Unusual transformations in MBH-type reactions of chromone-2-carbaldehydes with acrylonitrile and methyl acrylate have been explored and the structures of the unexpected products have been established using 1- and 2-D NMR, HRMS and X-ray crystallographic techniques. Attention has also been given to the synthesis of 3-(halomethyl)coumarins via the MBH reaction, and their subsequent Michaelis-Arbuzov reactions with triethyl phosphite. An exploratory study of the kinetics of the phosphonation reaction has been undertaken and the regio-selectivity of nucleophilic attack at the 4- and 1'-positions in the 3-chloro- and 3-(iodomethyl)coumarins has been investigated by calculating Mulliken charges, LUMO surfaces and Fukui condensed local softness functions.
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Copolymerizing Acrylonitrile and Methyl Acrylate by RAFT for Melt Processing Applications: A Synthetic Investigation of the Effects of Chain Transfer Agent, Initiator, Temperature, and SolventBeck, Susan Ashley 23 June 2014 (has links)
Statistical copolymers of acrylonitrile (AN) and methyl acrylate (MA) were successfully prepared and characterized using reversible addition-fragmentation chain transfer (RAFT) copolymerization. A typical copolymer was charged with 15 wt. % MA content. This thesis describes a systematic variation of the RAFT copolymerization variables to optimize this system. In particular, the effects of chain transfer agent, initiator, temperature, and solvent on the copolymer properties were studied. / Master of Science
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Determination of Reactivity Ratios for Acrylonitrile/Methyl Acrylate Radical Copolymerization Via Nonlinear Methodologies Using Real Time FTIRWiles, Kenton Broyhill 11 September 2002 (has links)
Reactivity ratios for the homogeneous free radical initiated copolymerization of acrylonitrile and methyl acrylate were measured by NMR on isolated, low conversion copolymers and by real time in situ FTIR. The system utilized azobisisobutyronitrile (AIBN) initiator in dimethyl formamide (DMF) at 62°. The FTIR technique allowed rapid generation of extensive copolymer compositions, which permitted application of nonlinear least squares methodology for the first time to this copolymer system. Thus, reactivity ratios at the 95% confidence level were determined to be 1.29 ± 0.2 and 0.96 ± 0.2 for acrylonitrile and methyl acrylate, respectively. The results are useful for the development of acrylonitrile (<90%) melt processable copolymer fibers and films, which could include precursors for carbon fibers. / Master of Science
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Synthesis and Characterization of Solution and Melt Processible Poly(acrylonitrile-co-methylacrylate) statistical copolymersPisipati, Padmapriya 10 April 2015 (has links)
Polyacrylonitrile (PAN) and its copolymers are used in a wide variety of applications ranging from textiles to purification membranes, packaging material and carbon fiber precursors. High performance polyacrylonitrile copolymer fiber is the most dominant precursor for carbon fibers. Synthesis of very high molecular weight poly(acrylonitrile-co-methyl acrylate) copolymers with weight average molecular weights of at least 1.7 million g/mole were synthesized on a laboratory scale using low temperature, emulsion copolymerization in a closed pressure reactor. Single filaments were spun via hybrid dry-jet gel solution spinning. These very high molecular weight copolymers produced precursor fibers with tensile strengths averaging 954 MPa with an elastic modulus of 15.9 GPa (N = 296). The small filament diameters were approximately 5 'm. Results indicated that the low filament diameter that was achieved with a high draw ratio, combined with the hybrid dry-jet gel spinning process lead to an exponential enhancement of the tensile properties of these fibers.
Carbon fibers for polymer matrix composites are currently derived from polyacrylonitrile copolymer fiber precursors where solution spinning accounts for ~40 % of the total fiber production cost. To expand carbon fiber applications into the automotive industry, the cost of the carbon fiber needs to be reduced from $8 to ~$3-5. In order to develop an alternative melt processing route several benign plasticizers have been investigated. A low temperature, persulfate-metabisulfite initiated emulsion copolymerization was developed to synthesize poly(acrylonitrile-co-methyl acrylate) copolymers with acrylonitrile contents between 91-96 wt% with a molecular weight range of 100-200 kg/mol. This method was designed for a potential industrial scale up. Furthermore, water was investigated as a potential melting point depressant for these copolymers. Twenty-five wt% water lead to a decrease in the Tm of a 93/7 wt/wt % poly(acrylonitrile-co-methyl acrylate) of Mw = 200 kg/mol to 160 0C as measured via DSC.
Glycerin, ethylene glycol and glycerin/water combinations were investigated as potential plasticizers for high molecular weight (~200,000 g/mol), high acrylonitrile (93-96 mole:mole %) content poly(acrylonitrile–co-methyl acrylate) statistical copolymers. Pure glycerin (25 wt %) induced crystallization followed by a reduced "Tm" of about 213 °C via DSC. However this composition did not melt process well. A lower MW (~35 kg/mol) copolymer did extrude with no apparent degradation. Our hypothesis is that the hydroxyl groups in glycerin (or water) disrupt the strong dipole-dipole interactions between the chains enabling the copolymer endothermic transition (Tm) to be reduced and enable melting before the onset of degradation. Additionally high molecular weight (Mw = 200-230 kg/mol) poly(acrylonitrile–co-methyl acrylate) copolymers with lower acrylonitrile content (82-85 wt %) were synthesized via emulsion copolymerization and successfully melt pressed. These materials will be further investigated for their utility in packaging applications. / Ph. D.
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Synthesis, Characterization, Processing and Physical Behavior of Melt-Processible Acrylonitrile Co- and Terpolymers for Carbon Fibers: Effect of Synthetic Variables on Copolymer SynthesisJohnson, Harry Dale 26 May 2006 (has links)
A novel photocrosslinkable and melt processible terpolymer precursor for carbon fibers has been successfully synthesized and characterized. The terpolymer was synthesized by an efficient emulsion polymerization route and has a typical composition of acrylonitrile/ methyl acrylate/acryloyl benzophenone in the molar ratio of 85/14/1. This thesis describes a systematic variation of the polymerization variables in the emulsion polymerization which may further enhance the system. In particular, the effects of chain transfer agent, initiator, and surfactant concentration on the polymer properties were studied. / Master of Science
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The influence of reactive modification on the compatibility of polyolefins with non-olefinic thermoplasticsLim, Henry C. A. January 2011 (has links)
Polyethylene (PE) resins being non-polar in nature and having a high degree of crystallinity have limited miscibility and compatibility when blended with polar polymers. The miscibility and compatibility of these blends are generally worsened when they are prepared by direct injection moulding without a precompounding process. Such situations are commonly encountered in particular by polymer converters when blending colour and/or additive concentrates, commonly known as masterbatches. Typically, masterbatches are mixtures containing high loading of pigments and/or additives predispersed in a suitable solid vehicle (commonly known as carrier) such as a polyethylene resin. These masterbatches are usually used for the colouration of a wide range of polymers and the carrier used must therefore be compatible with these matrix (host) polymers. The preliminary stage of this study involved the investigation of the properties of blends based on high density polyethylene (HDPE) and a range of engineering thermoplastics (ABS, PC, PBT, PA6), prepared by injection moulding. Five different types of compatibilisers namely, ethylene-vinyl acetate (EVA) copolymer, ethylene-methyl acrylate (EMA) copolymer, ethylene-glycidyl methacrylate (E-GMA) copolymer, ethylene-methyl acrylateglycidyl methacrylate (E-MA-GMA) terpolymer and maleic anhydride grafted HDPE (HDPE-g-MAH) copolymer were evaluated with respect to their efficiencies in compatibilising HDPE with the four engineering polymers. The pre-compounded HDPE/compatibiliser binary blends at 2 different blend ratios (1:1 and 3:1) were added at 15 wt% concentration to each engineering thermoplastics and test samples were produced directly by injection moulding. Results of mechanical testing and characterisation of the blends showed that glycidyl methacrylate compatibilisers, E-MA-GMA, in particular have the most universal compatibilising effectiveness for a range of engineering thermoplastics including ABS, PC, PBT, and PA6. Blends compatibilised with E-MA-GMA compatibiliser had the best notched impact performance irrespective of matrix polymer type. The presence of an acrylic ester (methyl acrylate) comonomer in E-MA-GMA resulted in increased polarity of the ii compatibiliser leading to improved miscibility with the polar matrix polymers demonstrated by fine blend morphologies, melting point depression and reduction in crystallinity of the HDPE dispersed phase. The second stage of this study involved the reactive modification of HDPE using a low molecular weight di-functional solid diglycidyl ether of bisphenol A (DGEBA) type epoxy resin compatibilised with HDPE-g-MAH in an attempt to improve its compatibility with ABS, PBT and PA6. The maleic anhydride moieties in HDPE-g-MAH served as reactive sites for anchoring the epoxy moieties while the HDPE backbone was miscible with the HDPE resin. An excessive amount of reactive groups resulted in the formation of crosslinked gels while the addition of EVA co-compatibiliser helped in the reduction of gel content and further improved the dispersion of the epoxy. The effectiveness of epoxy grafted HDPE (with and without EVA co-compatibiliser) in compatibilising ABS/HDPE, PBT/HDPE, and PA6/HDPE was investigated by injection moulding of 5 wt% functionalised HDPE with these matrix polymers into test bars for mechanical testing, and characterisation by differential scanning calorimtery (DSC) and optical microscopy. The reactively functionalised HDPE blends, improved the mechanical properties of ABS and PA6 blends especially with EVA as co-compatibiliser. However, the mechanical properties of PBT blends were unmodified by the functionalised HDPE which was believed to be due to end-capping of the PBT chain-ends by ungrafted epoxy resins.
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Poly(acrylonitrile/methyl acrylate) copolymers and clay nanocomposites : structural and property relationshipsZengeni, Eddson 12 1900 (has links)
Thesis (MSc (Chemistry and Polymer Science))--University of Stellenbosch, 2009. / Thesis submitted in partial fulfillment of the requirements for the degree
of Master of Science (Polymer Science)
at University of Stellenbosch. / ENGLISH ABSTRACT: The preparation of poly(acrylonitrile/methyl acrylate) [poly(AN-co-MA)] copolymers and
poly(AN-co-MA)/clay nanocomposites, via emulsion polymerization, their characterisation,
and the relationships between their molecular structures and physical properties are described.
The copolymer composition was varied, and the properties of the products were analysed and
correlated to copolymer composition.
The free volume properties of the copolymer were dependent on the glass transition
temperature (Tg), which is dependant on the copolymer composition. The copolymer
crystallinity decreased with increasing MA content. The decrease in crystallinity and increase
in both o-Ps lifetime and o-Ps intensity with decreasing Tg was caused by the enhanced chain
mobility brought about by the incorporation of methyl acrylate.
The poly(acrylonitrile-co-methyl acrylate)/clay nanocomposites with 60% AN:40%
MA (mol:mol) ratio were prepared using montmorillonite clay modified via adsorption, using
2-acrylamido-2-methyl-1-propanesulphonic acid (AMPS), via in-situ intercalation
polymerization. The poly(AN-co-MA)/clay nanocomposites with different clay loadings
showed no difference in morphology. They exhibited improved thermomechanical properties
and higher thermal stability than the neat copolymers.
The melt rheology results of these nanocomposites showed an improved storage
modulus as well as increased shear thinning behaviour with increasing clay content. However,
the nanocomposites exhibited long-time relaxation behaviour and their chemical structures
evolved during analysis. This was attributed to cyclisation reactions taking place at the
temperature used during the oscillatory tests.
The sorption isotherms of water vapour in these nanocomposites followed a dualmode
sorption behaviour (BET type II mode). Hysteresis was observed in sorption/desorption
isotherms of these nanocomposites. The equilibrium water uptake was higher in the nanocomposites compared to the neat copolymers, and it increased with increasing clay
content, especially at high water activities (0.8).
Although diffusion and permeability decreased with increasing clay content the
solubility increased due to the hydrophilic nature of the clay. Despite the decrease in diffusion
and permeability parameters the free volume hole radius of the nanocomposites remained constant, but a slight decrease in free volume hole number was observed. / AFRIKAANSE OPSOMMING: Die bereiding van poli(akrilonitriel/metielakrilaat) [poli(AN-ko-MA)] kopolimere en
poli(AN-ko-MA)/klei nanosamestellings deur middel van emulsiepolimerisasie, hul
karakterisering asook die ooreenkoms tussen hul molekulêre strukture en fisiese eienskappe is
beskryf. Die kopolimeersamestelling is gevarieer, en eienskappe is geanaliseer en dan
gekorreleer met die kopolimeersamestelling.
Die vrye-volume eienskappe van die kopolimeer was afhanklik van die
glasoorgangstemperatuur (Tg) wat weer afhanklik is van die kopolimeersamestealling. Die
kristalliniteit van die kopolimeer het verminder met die hoeveelheid MA teenwoordig. Die
afname in kristalliniteit en toename in beide die o-Ps leeftyd en o-Ps intensiteit met afname in
Tg is veroorsaak deur die beter kettingbeweegbaarheid wat veroorsaak is deur die byvoeging
van metielakrilaat.
Die poli(akrilonitriel-ko-metielakrilaat)/klei nanosamestellings met 60% AN:40% MA
(mol:mol) verhouding is berei deur die gebruik van montmorillonietklei, gemodifiseer deur
die adsorpsie van 2-akrielamido-2-metiel-1-propaansulfoonsuur (AMPS) deur middel van 'n
in-situ interkaleringspolimerisasie. Die poli(AN-ko-MA)/klei nanosamestellings het, ten spyte
van die verskillende hoeveelhede klei wat gebruik is, geen verandering in morfologie getoon
nie. Hulle het wel beter termodinamiese eienskappe en hoër termiese stabiliteit as die
oorspronklike kopolimere getoon.
Die smeltreologie resultate van hierdie nanosamestellings het ‘n beter stoormodulus
getoon, sowel as toenemende skuifverdunningsgedrag met 'n verhoogde klei inhoud. Tog het
die nanosamestellings lang tyd-ontspanningsgedrag getoon en die chemiese struktuur het
verander tydens analise. Dit word toegeskryf aan die sikliese reaksies wat plaasvind by die
temperatuur wat gebruik is tydens die ossillatoriese toetse.
Die sorpsie isoterme van waterdamp in hierdie nanosamestellings het ‘n dubbel-styl
sorpsiegedrag gevolg (BET tipe II styl). Histerese is waargeneem in sorpsie/desorpsie isoterme van hierdie nanosamestellings. Die ewewig in wateropname van die
nanosamestellings was hoër as vir dié van die oorspronklike kopolimere en dit het toegeneem
met 'n toenemende klei inhoud, veral by hoë humiditeit (0.8).
Al het die diffusie en deurlaatbaarheid afgeneem met 'n toename in die klei inhoud,
het die oplosbaarheid toegeneem as gevolg van die hidrofiliese karakter van die klei. Ten
spyte van die afname in diffusie en deurlaatbaarheidsparameters, het die radius van die vryevolume
openinge van die nanosamestellings konstant gebly, maar ‘n klein afname in die aantal vrye-volume openinge is gevind.
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Ternary Nanocomposites Of High Density, Linear Low Density And Low Density PolyethylenesUcar, Egemen 01 June 2007 (has links) (PDF)
In this study, the effects of organoclay loading, compatibilizer loading and polyethylene type on the morphology, rheology, thermal properties and mechanical properties of polyethylene/compatibilizer/organoclay nanocomposites were investigated. As compatibilizer, terpolymer of ethylene-methacrylate-glycidyl methacrylate (Lotader® / AX8900), as organoclay Cloisite® / 15A were used. All samples were prepared by a co-rotating twin screw extruder, followed by injection molding.
Considering ternary nanocomposites, highest impact strength results were obtained with 10% compatibilizer plus 2% organoclay / highest yield stress, elastic modulus, flexural strength, flexural modulus were obtained with 5% compatibilizer plus 4-6% organoclay.
DSC data indicated that addition of organoclay and compatibilizer did not change the melting point remarkably / on the other hand it affected the crystallinity. The organoclay used had no nucleation effect on polyethylene, and the compatibilizer decreased the crystallinity of the matrix.
X-ray diffraction showed that in all ternary nanocomposites and in binary nanocomposite of high density polyethylene with organoclay, layer separation associated with intercalation of the clay structure occurred,. The highest increase of interlayer gallery spacing was obtained with 10% compatibilizer plus 2% organoclay, which were 25%, 28% and 27% for HDPE, LLDPE and LDPE matrices respectively.
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PREPARATION AND CHARACTERIZATION OF SOME UNUSUAL ELASTOMERIC AND PLASTIC COMPOSITESRAJAN, GURU SANKAR 11 June 2002 (has links)
No description available.
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Efeito da adi??o do poli(etileno acrilato de metila) (ema) e da fibra de linter de algod?o nas propriedades do poli(tereftalato de etileno) reciclado (petrec)Pereira, Laurenice Martins 28 December 2014 (has links)
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Previous issue date: 2014-12-28 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / The development of new materials to fill the demand of technological advances is
a challenge for many researchers around the world. Strategies such as making
blends and composites are promising alternatives to produce materials with
different properties from those found in conventional polymers. The objective of
this study is to evaluate the effect of adding the copolymer poly(ethylene methyl
acrylate) (EMA) and cotton linter fibers (LB) on the properties of recycled
poly(ethylene terephthalate) (PETrec) by the development of PETrec/EMA blend
and PETrec/EMA/LB blend composite. In order to improve the properties of these
materials were added as compatibilizers: Ethylene - methyl acrylate - glycidyl
methacrylate terpolymer (EMA-GMA) and maleic anhydride grafted polyethylene
(PE-g-MA). The samples were produced using a single screw extruder and then
injection molded. The obtained materials were characterized by
thermogravimetry (TG), melt flow index (MFI) mensurements, torque rheometry,
pycnometry to determinate the density, tensile testing and scanning electron
microscopy (SEM). The rheological results showed that the addition of the EMA
copolymer increased the viscosity of the blend and LB reduces the viscosity of
the blend composite. SEM analysis of the binary blend showed poor interfacial
adhesion between the PETrec matrix and the EMA dispersed phase, as well as
the blend composite of PETrec/EMA/LB also observed low adhesion with the LB
fiber. The tensile tests showed that the increase of EMA percentage decreased
the tensile strength and the Young s modulus, also lower EMA percentage
samples had increased the elongation at break. The blend composite showed an
increase in the tensile strength and in the Young`s modulus, and a decrease in
the elongation at break. The blend formulations with lower EMA percentages
showed better mechanical properties that agree with the particle size analysis
which showed that these formulations presented a smaller diameter of the
dispersed phase. The blend composite mechanical tests showed that this
material is stronger and stiffer than the blend PETrec/EMA, whose properties have
been reduced due to the presence of EMA rubbery phase. The use of EMA-GMA
was effective in reducing the particle size of the EMA dispersed phase in the
PETrec/EMA blend and PE-g-MA showed evidences of reaction with LB and
physical mixture with the EMA / O desenvolvimento de novos materiais para atender as necessidades dos
avan?os tecnol?gicos ? um desafio enfrentado por pesquisadores de todo o
mundo. No que diz respeito aos materiais polim?ricos, estrat?gias como a
confec??o de blendas e comp?sitos s?o alternativas promissoras para atender a
demanda por materiais com propriedades diferentes das encontradas nos
pol?meros convencionais. O objetivo deste trabalho ? avaliar o efeito da adi??o
do copol?mero poli(etileno-acrilato de metila) (EMA) e da fibra de linter de
algod?o (LB) nas propriedades do poli(tereftalato de etileno) reciclado (PETrec).
Para isto, foram desenvolvidos a blenda PETrec/EMA e o comp?sito da blenda
PETrec/EMA/LB. Com o intuito de melhorar as propriedades destes materiais
foram adicionados agentes compatibilizantes: terpol?mero etileno-acrilato de
metila-metacrilato de glicidila (EMA-GMA) e o polietileno enxertado com anidrido
mal?ico (PE-g-MA). As misturas foram produzidas por meio de uma extrusora
monorosca e, em seguida, moldados por inje??o. As caracteriza??es realizadas
foram termogravimetria (TG), medida de ?ndice de fluidez (MFI), reometria de
torque, determina??o da densidade por picnometria, ensaio de tra??o uniaxial e
microscopia eletr?nica de varredura (MEV). Os resultados reol?gicos mostraram
que a adi??o do copol?mero EMA aumentou a viscosidade da mistura e o LB
reduziu a viscosidade da blenda PETrec/EMA. A an?lise por MEV da blenda
bin?ria mostrou baixa ades?o interfacial entre a matriz de PETrec e a fase
dispersa de EMA, assim como no comp?sito da blenda PETrec/EMA/LB, tamb?m
observou-se uma baixa ades?o com a fibra de LB. Os ensaios de tra??o
mostraram que o aumento da porcentagem de EMA diminuiu a resist?ncia
m?xima e o m?dulo de elasticidade, e, para as formula??es com menor
porcentagem de EMA verificou-se um aumento do alongamento na ruptura. O
comp?sito da blenda apresentou um aumento na resist?ncia m?xima e no
m?dulo de elasticidade, e uma redu??o no alongamento de ruptura. As
formula??es da blenda com menores porcentagens de EMA apresentaram
propriedades mec?nicas melhores, que corrobora com as an?lises de tamanho
de part?cula que mostraram que estas formula??es apresentaram menor
di?metro m?dio de fase dispersa. Os resultados de ensaios mec?nicos do
comp?sito da blenda mostraram que essa mistura resultou em um material com maior resist?ncia mec?nica e rigidez do que a blenda PETrec/EMA, cujas
propriedades foram reduzidas em fun??o da fase borrachosa EMA. O uso do
EMA-GMA foi eficiente na redu??o do tamanho de part?culas da fase dispersa do
EMA na blenda PETrec/EMA e o PE-g-MA apresentou ind?cio de rea??o com o
LB e mistura f?sica com o EMA
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