Spelling suggestions: "subject:"copolymers"" "subject:"kopolymers""
351 |
Synthesis and characterisation of hybrid graft copolymers of polydimethylsiloxane and polymethylmethacrylateKrugel, Gretha 12 1900 (has links)
Thesis (MSc (Chemistry and Polymer Science))--University of Stellenbosch, 2007. / Hybrid graft copolymers of polydimethylsiloxane (PDMS) and polymethylmethacrylate
(PMMA) were synthesised. PDMS macromonomers were synthesised anionically from
the cyclic D3 monomer. This living polymerisation was terminated with a [3-
(methacryloxy)propyl]-dimethylchlorosilane terminating agent which resulted in the
functionalised macromonomer. These PDMS macromonomers and MMA monomer were
copolymerised to form PMMA-g-PDMS hybrid copolymers by conventional free radical
reactions. Synthesised and commercial methacryloxy-functionalised PDMS
macromonomers having a range of molar masses were copolymerised with MMA to form
graft copolymers of various chemical compositions. PDMS content in the graft
copolymers could be varied by the amount of PDMS incorporated into the copolymer as
well as by varying the length of the PDMS side chains. Size exclusion chromatography
(SEC) results confirmed low PDI’s for the PDMS macromonomers synthesised
anionically. NMR studies allowed characterisation of the synthesised PDMS
macromonomers and PMMA-g-PDMS copolymers. It also allowed the determination of
relative ratios of PMMA:PDMS in the graft copolymers. Gradient elution chromatography
(GEC) was used successfully to monitor the presence and removal of the PDMS
macromonomer from the graft copolymer products. The influence of PDMS content of
the graft copolymers on retention time was also evaluated using this technique. Two
dimensional chromatography confirmed the formation of PMMA-g-PDMS copolymer as
well as PMMA homopolymer during some of the grafting reactions. GEC in the first
dimension was coupled to SEC in the second dimension. PAS-FTIR studies allowed
chemical characterisation of the graft copolymer and confirmed surface segregation of
the PDMS. Atomic force microscopy (AFM) was also used to study the surface
segregation of PDMS and looked at the relationship between surface polarity and
increasing PDMS content. The study showed the effect of thermal treatment on the
surface morphology of the hybrid polymers. Corona treatment was used to modify the
surface structure of the graft copolymer films. Contact angle studies provided evidence
of hydrophobic loss and recovery after corona for the hybrid polymer materials
containing PDMS. This is one of the first reported examples of hydrophobicity recovery
in these types of hybrid materials after corona treatment. Slow positron beam studies
highlighted the formation of a thin silica like layer on the surface of the films after corona
similar to that observed for pure cross-linked PDMS compounds. The positron studies
enabled estimation of the thickness of the silica like layer.
|
352 |
The effect of molecular architecture on the properties of propylene impact copolymersBasson, N. C. 03 1900 (has links)
Thesis (MSc (Chemistry and Polymer Science))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: Impact polypropylene copolymers (IPPC) are important commercial materials, but their morphology and molecular architecture are not yet fully understood. In this study the focus was on selectively removing specific fractions from the original IPPC, recombining the remaining fractions, and studying the properties of these recombined polymers.
It was found that some properties of the samples changed remarkably, depending on the fraction of material that was removed before recombination. For example, the degree of phase separation and the crystalline morphology of the recombined materials varied noticeably.
During the study an effective way of staining samples for transmission electron microscopy (TEM) was developed. Furthermore, a comparison of fourier transform infrared spectroscopy (FTIR), with TEM and scanning electron microscopy (SEM) results, revealed a hitherto unreported relationship between phase separation.
Absorption bands appeared at 1100 cm-1 and 1080 cm-1 in the FTIR spectra and appear to be an indication of phase separation. It was further established that specific copolymer fractions present in the original polymer affect not only the morphology of the final polymer, but also the hardness and impact resistance. / AFRIKAANSE OPSOMMING: Impak polipropileen kopolimere (IPPK) is belangrike kommersïele materiale, maar die kennis met betrekking tot die morfologie en molekulere argitektuur van die materiale is nog gebrekkig. Tydens hierdie studie was die fokus op die selektiewe verwydering van spesifieke fraksies van die oorspronklike IPPK, herkombinering van die oorblywende fraksies, en die studie van die eienskappe van hierdie herkombineerde polimeriese materiale.
Daar is gevind dat sommige van die eienskappe van die herkombineerde materiale daadwerklik verskil van die oorspronklike materiaal, en dat die verskille direk verband hou met die spesifieke fraksie wat uit die oorspronklike materiaal verwyder is. Die mate van fase-skeiding asook die kristal-morfologie van die herkombineerde materiaal het opmerklik verskil van die oorspronklike.
Tydens die studie is n effektiewe manier ontwikkel om die materiale te vlek vir transmissie elektron-mikroskopie (TEM). Verder is daar ‘n verband tussen die resultate verkry deur Fourier Transform infrarooi spektroskopie (FTIS) en die verkry met TEM en skandeer elektron mikroskopie (SEM) vasgestel. Die verwantskap tussen FTIS en fase-skeiding is tot dusver nie in die wetenskaplike literatuur vermeld nie. Meer spesifiek is daar gevind dat absorbsie-bande sigbaar by 1100 cm-1 en 1080 cm-1 in die FTIS spektra ‘n aanduiding van fase skeiding kan wees. Dit was verder vasgestel dat spesifieke kopolimeer fraksies wat teenwoordig is in die oorspronklike IPPK, nie alleen die morfologie van die materiaal beinvloed nie, maar ook die hardheid en impak-weerstand van die materiaal.
|
353 |
RAFT mediated polysaccharide copolymersFleet, Reda 12 1900 (has links)
Thesis (MSc (Chemistry and Polymer Science))--University of Stellenbosch, 2006. / Cellulose, one of the most abundant organic substances on earth, is a linear polymer
of D-glucose units joined through 1,4-β-linkages. Cellulose is however not easily
processed without chemical modification. A number of techniques exist for the
modification of cellulose, of which the viscose process is one of the most widely
applied. Grafting of synthetic polymeric chains onto or from cellulosic materials is an
useful technique that can be used to combine the strengths of synthetic and natural
polymers dramatically, so changing the properties of cellulosic materials (pulp,
regenerated cellulose, cellulose derivatives).
In this study five model xanthate (Reversible Addition-Fragmentation chain Transfer
(RAFT)/Macromolecular Design through Interchange of Xanthates (MADIX)) agents,
namely, monofunctional, difunctional, trifunctional and tetrafunctional species of the
form S=C(O-Z)-S-R, with different leaving groups and different activating moieties,
were prepared and then studied to determine the feasibility of cellulose modification
via addition fragmentation processes. These agents were characterized by Nuclear
Magnetic Resonance spectroscopy (NMR), Fourier Transform Infrared spectroscopy
(FT-IR) and Ultraviolet spectroscopy (UV). Polyvinyl acetates (PVAc) in the form of
linear, three armed and four armed star shaped polymers were then successfully
synthesized in reactions mediated by these xanthate RAFT/MADIX agents
Xanthates were applied to polysaccharide materials using the viscose process
(xanthate esters were formed directly on a cellulosic substrate, with subsequent
alkylation) Grafting reactions were then conducted with the polysaccharides; cellulose
was modified with vinyl acetate, [this is an example of a surface modification of
natural polymers that is of interest in various industries, such as textiles and paper
manufacture].
Analysis of the graft copolymers was conducted via Size Exclusion Chromatography
(SEC), Liquid Adsorption Chromatography (LAC), Thermogravimetric Analysis
(TGA), and FT-IR.
Polyvinyl acetate was successfully grafted onto three polysaccharides (cellulosic
materials), namely Hydroxyl Propyl Cellulose (HPC), Methyl Cellulose (MC) and
cellulose. The study showed that the modification of cellulosic substrates with defined
grafts of vinyl acetate can be easily achieved through minor modifications to existing
industrial techniques.
|
354 |
Novel synthesis of block copolymers via the RAFT processBowes, Angela 12 1900 (has links)
Thesis (MSc (Chemistry and Polymer Science))--University of Stellenbosch, 2007. / The synthesis of complex architectures, namely block copolymers with tailored enduse
properties, is currently an important research area in academia and industry. The
challenge is finding a versatile polymerization technique capable of controlling the
molecular properties of the formed copolymers, which in turn determines their
macroscopic properties. Reversible addition-fragmentation chain transfer (RAFT)-
mediated living polymerization is a robust technique capable of producing controlled
polymer products. With the great advances in living polymerization techniques and
the environmental awareness of society there is an increasing demand to produce
these polymer products via the RAFT living technique in heterogeneous media.
Conventional emulsion and miniemulsion polymerization present various problems
when used to produce polymers mediated by the RAFT process. There is an inherent
need to find cost effective and flexible operating conditions to conduct RAFT
polymerization in heterogeneous media with the ability to produce well-defined block
copolymers.
In this study the use of three novel trithiocarbonate RAFT agents to produce welldefined
AB-type, ABA-type and star block copolymers via the RAFT process was
investigated. Optimal operating conditions for the production of living block
copolymers in homogenous and heterogeneous media were determined. The main
focus was on the development of the RAFT process in heterogeneous media to
efficiently produce block copolymer latex products. The RAFT-mediated
miniemulsion polymerization system stabilized with non-ionic surfactants was
thoroughly investigated. The ability of the ab initio and in situ RAFT-mediated
emulsion polymerization systems to produce controlled latexes was demonstrated.
Controlled block copolymer products were successfully synthesized in homogenous
and heterogeneous media via the RAFT process when the optimum reaction
conditions were chosen.
|
355 |
Synthesis and characterization of electrospun organic-inorganic hybrid graft copolymer nanofibers of poly(methyl methacrylate) and polydimethylsiloxaneSwart, Morne 12 1900 (has links)
Thesis (MSc (Chemistry and Polymer Science))--University of Stellenbosch, 2007. / Two series of poly(methyl methacrylate)-graft-poly(dimethylsiloxane) copolymers were synthesized via conventional free radical copolymerization of methylmethacrylate and monomethacryloxypropyl terminated PDMS macromonomers of different lengths. It is shown how these copolymers can be electrospun to produce the copolymer nanofibers. The affects of copolymer compositions, the electrospinning tip-to-collector (TCD) distance and the concentration of the polymer solution on the fiber morphology are discussed. Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) were used to establish the surface topography as well as the fiber morphology of the electrospun copolymer nanofibers. It is also shown that these nanofibers produce superhydrophobic surfaces where the preferential surface segregation of the PDMS component is combined with the roughness of the nanofiber surface. It is shown that after exposure of these nanofiber surfaces to corona discharge, the initial superhydrophobic surfaces become easily wettable. The samples show the phenomena of hydrophobicity recovery after corona exposure. The rate and extent of this recovery depends on the PDMS content of the nanofibers as well as the time of corona treatment. The hybrid copolymer nanofibers were evaluated as potential reinforcing fillers for cross linked polydimethylsiloxane compounds. The fibers show a remarkably good distribution in the PDMS matrix and show a dramatic improvement in the mechanical
properties of the composites.
|
356 |
The development of analytical techniques for studying degradation in impact polypropylene copolymersDe Goede, Elana 03 1900 (has links)
Thesis (DSc (Chemistry and Polymer Science))--University of Stellenbosch, 2009. / Unstabilised polyolefins are susceptible to degradation when exposed to molecular oxygen, heat, irradiation as well as chemical and mechanical stimuli. Oxidation leads to changes in molecular properties such as molecular weight, molecular weight distribution, chemical composition, chemical composition distribution and crystallisability. Conventional analytical techniques are of limited use when studying the degradation of heterogeneous materials such as impact polypropylene copolymers (ICPP). These copolymers consist of a number of components of different monomer contents, isotacticity and crystallinity, ranging from amorphous EPR to highly crystalline polypropylene. The individual components are affected differently by degradation, leading to heterogeneity within the degradation of impact copolymers. Novel analytical approaches that acknowledge the heterogeneity in sample composition are needed to study the degradation behaviour of such heterogeneous materials.
This study describes the combination of fractionation and hyphenated techniques with conventional analyses for extensive structural characterisation of complex impact copolymers as well as their degradation behaviour. Temperature rising elution fractionation (TREF) coupled to conventional techniques such as size exclusion chromatography (SEC), Fourier-Transform infrared spectroscopy (FTIR), Carbon-13 nuclear magnetic resonance (13C-NMR) and differential scanning calorimetry (DSC) indicated the ICPPs in question to consist of four main components, namely ethylene-propylene random copolymers (EPR), isotactic PP (iPP), as well as semi-crystalline ethylene-propylene copolymers (EPC) and lower isotacticity PP. The degradation of an ICPP was studied by a multi-component analysis procedure consisting of TREF coupled to SEC, 13C-NMR, as well as SEC-FTIR. Results obtained by this procedure indicated the change in crystallisability of the bulk sample observed by TREF, crystallisation analysis fractionation (CRYSTAF) and DSC to be the result of the preferential degradation of the iPP phase. Degradation of ICPPs initiates within this phase where chain scission and carbonyl group insertion leads to a change in the crystallisability of iPP chains. During TREF of degraded bulk ICPPs, the degraded iPP molecules elute at lower elution temperatures, depending on their degree of degradation. The other components of the copolymer were degraded to a lesser extent. Degradation products were also found to be heterogeneously distributed across the molecular weight distribution of each fraction, with a higher concentration appearing at the low molecular weight side. The multi-component analysis procedure was also used to study the difference in degradation behaviour between ICPPs of different comonomer content, isotacticity and crystallinity.
The spatial heterogeneity of degradation within ICPPs was studied by Fourier-Transform infrared microspectroscopy (FTIR-μS). A heterogeneous distribution of degradation products was found across the depth of thicker sample specimens. These results were compared to those obtained by conventional layer-by-layer milling followed by SEC, FTIR and CRYSTAF. The principles of degradation within thick samples were similar to that observed for thin films, although additional contributions by sample morphology and oxygen diffusion were detected.
|
357 |
Novel siloxane block copolymersStaisch, Ingrid 12 1900 (has links)
Thesis (PhD (Chemistry and Polymer Science))--Stellenbosch University, 2008. / The research presented in this dissertation was concerned with the living radical
polymerization (LRP) of an amphiphilic, water-soluble, bi-substituted and
biologically compatible acrylamide derivative, namely n-acryloylmorpholine (NAM).
The primary objective of this research was the synthesis of novel block
copolymers containing poly(dimethylsiloxane) (PDMS) and various chain lengths
of poly(acryloylmorpholine) (polyNAM) using a LRP technique, namely reversibleaddition
fragmentation chain transfer (RAFT) polymerization. This is the first report
on the synthesis of these block copolymers using RAFT polymerization. These
novel siloxane block copolymers were synthesized using a monohydroxyterminated
PDMS material which had to first be modified into a thiocarbonylthiocontaining
moiety in order for it to be used as macromolecular chain transfer agent
(macroCTA) in the RAFT copolymerization with NAM.
Suitable reaction conditions for the synthesis of these novel block copolymers had
to, firstly, be determined, and secondly, optimized. In order to determine suitable
reaction conditions, a series of homopolymerizations with NAM were first
performed in order to compare which chain transfer agent (CTA), solvent,
temperature etc. could possibly be best suited for the block copolymerizations of
PDMS-b-polyNAM. Reported in this work is the first account of the
homopolymerization of NAM and 2-(dodecylsulfanyl)thiocarbonylsulfanyl-2-methyl
propionic acid (DMP) as CTA using RAFT polymerization.
The resulting novel siloxane block copolymers are amphiphilic in nature and the
existence of these structures was confirmed by size exclusion
chromatography/multiangle light scattering (SEC/MALS), proton nuclear magnetic
resonance (1H-NMR) spectroscopy, gel elution chromatography (GEC) and
transmission electron microscopy (TEM). Interesting phase behaviour was
observed in the latter technique.
|
358 |
Novel electrospun fibres of amphiphilic organic-inorganic graft copolymers of poly(acrylonitrile)-graftpoly( dimethylsiloxane) for silicone composite reinforcementBayley, Gareth Michael 12 1900 (has links)
Thesis (PhD)--Stellenbosch University, 2011. / ENGLISH ABSTRACT: Novel silicone nanocomposites were prepared using poly(acrylonitrile) (PAN) based reinforcing
fibres as well as multi-walled carbon nanotubes (MWCNTs). Compatibility of the fibre fillers with
the silicone matrix required the synthesis of novel amphiphilic, organic–inorganic graft
copolymers of PAN and poly(dimethylsiloxane) (PAN-g-PDMS). These fibre precursor materials
were synthesised via the “grafting through” technique using conventional free radical
copolymerisation. The PDMS macromonomer content in the feed was varied from 5 wt% to 25
wt% and the molecular weights of the macromonomer were 1000 g.mol-1 and 5000 g.mol-1. The
solvent medium of the precipitation reaction was optimised at a volume ratio of 98% benzene to
2% dimethylformamide (DMF). Successful incorporation of PDMS yielded graft copolymer blend
materials of PAN-g-PDMS, blended with PAN homopolymer and unreacted PDMS
macromonomer. A gradient elution profile was developed to track the successful removal of the
PDMS macromonomer via hexane extraction. The gradient profile showed that as the PDMS
content in the feed increased, the number of graft molecules in the blend increased relative to
the number of PAN homopolymer molecules. The crystallisability of the PAN segments was
shown to decrease as the PDMS content increased. The synthesised polymer was used as
precursor material for the electrospinning of fibre fillers. The electrospinning of the precursor
material was successfully achieved using 100% DMF as electrospinning solution medium. The
amphiphilic nature of the precursor material in DMF resulted in self-assembled aggregate
structures in the electrospinning solution. An increasing PDMS content was shown to affect the
aggregation of the precursor material, and resulted in an increase in the solution viscosity. The
“gel-like” solutions limited the achievable fibre morphological control when altering conventional
electrospinning parameters such as voltage, tip-to-collector distance, and solution
concentrations. The rapid evaporation and stretching of the solution during electrospinning,
combined with the phase segregated amphiphilic molecules in solution and the crystallisation of
the PAN segments resulted in (non-equilibrium morphology) fully porous fibres. The crystallinity
was shown to decrease after electrospinning of the fibre precursor materials. Successful
incorporation of surface oxidised MWCNTs into the electrospun fibres was achieved. The
content of nanotubes was varied from 2 wt% to 32 wt%. The MWCNTs reduced the mean fibre
diameters by acting as cross-linkers between the PAN segments and increasing the solution
conductivity. The nanotubes dispersed well throughout the porous structure of the fibres and
aligned in the direction of the fibre axis. Fabrication of silicone composites containing nonwoven
and aligned fibre mats (with 8 wt% MWCNTs in the fibres, and without) was successfully achieved. The compatibilisation of the PDMS surface segregated domains allowed excellent
dispersion and interaction of the PAN based fibre fillers with the silicone matrix. Mechanical
analysis showed improved properties as the PDMS content in the fibre increased. The highest
PDMS content fibres did, however, exhibit decreased properties. This was ascribed to increased
PDMS (soft and weak) content, decreased crystallinity and increased fibre diameter (lower
interfacial area). Dramatic improvements in strength, stiffness, strain and toughness were
achieved. The most significant result was an increase in strain of 470%. The mechanical results
correlated with results of SEM analysis of the fracture surfaces. The dramatic improvements in
properties were a result of the fibre strength and ductility, as well as the mechanism of
composite failure. / AFRIKAANSE OPSOMMING: Nuwe silikonnanosamestellings is berei deur gebruik te maak van poli(akrilonitriel) (PAN)
gebaseerde versterkende vesels wat multi-ommuurde koolstof nanobuisies bevat het.
Versoenbaarheid van die vesels met die silikonmatriks het die sintese van nuwe amfifiliese,
organies–anorganiese ent-kopolimere van PAN en poli(dimetielsiloksaan) (PAN-g-PDMS)
benodig. Die vesel voorlopermateriaal is deur middel van ‘n “ent-deur” vryeradikaalkopolimerisasie
gesintetiseer. Die inhoud van die PDMS makromonomeer in die reaksie het
gewissel vanaf 5% tot 25%. Die gebruik van twee verskillende molekulêre massas
makromonomere is bestudeer (1000 en 5000 g.mol-1). Die optimale oplosmiddelmengsel vir die
neerslagreaksie was 'n volume verhouding van 98% benseen tot 2% dimetielformamied (DMF).
Suksesvolle insluiting van PDMS het versnitmateriale van PAN-g-PDMS kopolimere gemeng
met PAN homopolimere en ongereageerde PDMS makromonomere gelewer. 'n Gradiënteluering-
chromatografiese profiel is ontwikkel om die suksesvolle verwydering van die PDMS
makromonomere via heksaanekstraksie te bepaal. Die gradiëntprofiel het aangetoon dat indien
die PDMS inhoud in die reagense verhoog is, die aantal entmolekules relatief tot PAN
homopolimeermolekules ook verhoog het. 'n Toename in PDMS inhoud het egter 'n afname in
kristallisasie van die PAN segmente tot gevolg gehad. Die gesintetiseerde polimeer is gebruik
as die beginmateriaal vir die elektrospin van veselvullers. Die elektrospin van die beginmateriaal
was suksesvol wanneer 100% DMF as elektrospinoplosmiddel gebruik is. Die amfifiliese aard
van die beginmateriaal in DMF lei tot outokonstruksie van aggregaatstrukture in die
elektrospinoplossing. Toenemende PDMS inhoud beïnvloed die outokonstruksie van die
molekules in oplossing en het gelei tot 'n toename in die oplossings se viskositeit. Die "gelagtige"
oplossings beperk die haalbare vesel se morfologiese beheerbaarheid wanneer
konvensionele elektrospin parameters soos elektriese spanning, punt-tot-versamelaar afstand,
en oplossingkonsentrasies gewysig word. Die vinnige verdamping en strek van die oplossing
tydens elektrospin, gekombineer met die fase-geskeide amfifiliese molekules in oplossing en die
kristallisasie van die PAN segmente, het gelei tot (nie-ewewig morfologie) volledige poreuse
vesels. Die kristalliniteit van die veselbeginmaterial het afgeneem nadat elektrospin toegepas is.
Die insluiting van die oppervlak-geoksideerde multi-ommuurde koolstof nanobuisies in die
elektrogespinde vesels was suksesvol. Die inhoud van die nanobuisies het gewissel van 2 wt%
tot 32 wt%. Die MWCNTs het die gemiddelde veseldeursnit verminder deur op te tree as
kruisbinders tussen die PAN segmente van die molekules. Die nanobuisies was goed versprei
deur die poreuse struktuur van die vesels en dit was gerig in die rigting van die vesel-as. Bereiding van die silikonsamestellings bestaande uit nie-geweefde en gerigte veseloppervlakke
(met en sonder 8 wt% multi-ommuurde koolstof nanobuisies in die vesel) was suksesvol. Die
versoenbaarheid tussen die oppervlak van die PDMS-geskeide gebiede en die silikonmatriks
laat uitstekende verspreiding en interaksie van die PAN-gebaseerde veselvullers met die
silikonmatriks toe. Meganiese analise het aangetoon dat die fisiese eienskappe verbeter het
namate die PDMS inhoud in die vesel vermeerder het. Die vesels met die hoogste PDMS
inhoud het egter verswakte eienskappe getoon. Dit is toegeskryf aan ‘n verhoogde PDMS
inhoud (sag en swak), ‘n afname in kristalliniteit en ‘n verhoogde veseldeursnit (laer
grensoppervlakke). Dramatiese verbeterings in sterkte, styfheid, verlengbaarheid, vervorming
en taaiheid is bereik. Die mees betekenisvolle gevolg was 'n toename in die verrekking van
470%. Die meganiese resultate is gekorreleer met SEM ontleding van die brekingsoppervlakke.
Die veselkrag en vervormbaarheid, sowel as die meganisme van die splyting van die
samestellings, het tot die dramatiese verbeterings in die meganiese eienskappe gelei.
|
359 |
Synthesis and characterization of multiphase copolymersElhrari, Wael K. S. 12 1900 (has links)
Thesis (PhD)--Stellenbosch University, 2011. / ENGLISH ABSTRACT: Multiphase copolymers generally consist of copolymers where the disparate natures of each
of the segments results in complex phase-segregated morphologies in the solid state. The
outstanding properties and wide range of applications of multiphase copolymers has led to
the need for more sophisticated synthesis methods to produce copolymers with controlled
structures. Associated with developments in synthetic methods is the need to develop
suitable techniques to characterize these materials in order to obtain a better understanding
of their structure–property relationships.
The synthesis of multiphase copolymers presents many challenges. These are
related to the nature of the molecular requirements, were the monomers of each of the
different components may not be polymerized by all available polymerization techniques.
This has led to the need to combine different polymerization techniques to overcome such
limitations.
The focus of this study is the combination of living controlled polymerization
techniques, namely anionic polymerization and RAFT polymerization, with
hydroboration/autoxidation, to produce non-polyolefin block and graft copolymers. Block
copolymers were synthesized by coupling anionic polymerization and
hydroboration/autoxidation reactions. The first block segment was prepared via anionic
polymerization, and then end-functionalized with a suitable functional group (e.g. an allyl
group). A hydroboration/autoxidation reaction was then used to initiate the polymerization of
the second block by the slow addition of oxygen at room temperature.
Graft copolymers were synthesized using the 'grafting from' technique, by coupling
RAFT copolymerization with hydroboration/autoxidation reactions. The backbone polymer
was synthesized via RAFT copolymerization of symmetric and asymmetric monomer, after
which a hydroboration/autoxidation reaction was carried out to produce graft copolymers.
The hydroboration/hydroxylation reaction could also be used to modify an
unsaturated polymer chain. The EPDM rubber chain was modified by transforming the
double bond into an hydroxyl group, which could undergo an esterification reaction with an
acid chloride RAFT agent to produce the multifunctional RAFT polymer. This was used for
the controlled living free radical polymerization of the graft chains. Significant amounts of
homopolymerization in addition to graft formation were obtained.
Solid state NMR (SS NMR) and positron annihilation lifetime spectroscopy were used
to determine the compositional phase segregation point in the graft copolymers. The spin
diffusion data from the SS NMR provided insight into the seemingly anomalous positron data
at the phase segregation point. It is demonstrated how these two techniques can provide
complimentary data on the solid state morphology of these multiphase materials. / AFRIKAANSE OPSOMMING: In die algemeen bestaan multifase kopolimere uit segmente van verskillende aard wat
komplekse fase-geskeide-morfologie in die vastetoestand tot gevolg het. Die uitstekende
eienskappe en wye reeks toepassings van multifase kopolimere het daartoe gelei dat meer
gesofistikeerde sintesemetodes vir die bereiding van kopolimere met gekontrolleerde
strukture nodig was. Gepaardgaande met verwante ontwikkelings op die gebied van
sintesemetodes was dit nodig om gepaste analitiese tegnieke te ontwikkel vir die
karakterisering van hierdie verbindings, ten einde die struktuur–eienskap verwantskap van
hierdie materiale beter te verstaan.
Daar is egter baie uitdagings m.b.t. die sintese van hierdie multifase kopolimere. Dit
is afhanklik van die aard van die molekulêre vereistes waar die monomere van elk van die
verskillende komponente nie deur alle beskikbare polimerisasietegnieke gepolimeriseer kan
word nie. Dit het daartoe gelei dat verskillende polimerasietegnieke gekombineer is ten einde
hierdie beperkinge te oorbrug.
Die fokus van hierdie studie is die kombinering van lewende vry-radikaal
gekontrolleerde polimerisasietegnieke, naamlik anioniese polimerisasie en RAFTpolimerisasie,
met hidroborering/outoksidasie, om nie-olefiniese blok- en entkopolimere te
berei. Blok-kopolimere is berei deur die koppeling van anioniese polimerisasie en
hidroborering/outoksidasie reaksies. Die eerste bloksegment is berei via anioniese
polimerisasie en daarna is endfunksionering met 'n geskikte funksionele groep (bv. 'n
allielgroep) bewerkstellig. Daarna is 'n hidroborering/outoksidasie reaksie gebruik om die
polimerisasie van die tweede blok te inisieer d.m.v. die stadige toevoeging van suurstof by
kamertemperatuur.
Entkopolimere is berei deur gebruik te maak van die 'ent-vanaf' tegniek, d.m.v. die
koppeling van RAFT-kopolimerisasie met hidroborering/outoksidasie reaksies. Die
rugraatpolimeer is berei d.m.v. kopolimerisasie van simmetriese en nie-simmetriese
monomere waarna die hidroborering/outoksidasie reaksie uitgevoer is om sodoende
entkopolimere te vorm.
Die hidroborering/hidroksilasie reaksie kon ook gebruik word om 'n onversadigde
polimeerketting te wysig. Die EPDM rubberketting is gewysig deur die omskakeling van die
dubbelbinding in 'n hidroksielgroep, wat dan 'n esterifikasie reaskie kon ondergaan met 'n
suurchloried-RAFT verbinding, om sodoende die multifunksionele RAFT-polimeer te vorm.
Dit is gebruik vir die gekontrolleerde lewende vry-radikaalpolimerisasie van die entkettings.
Behalwe entvorming is 'n hoë mate van homopolimerisasie waargeneem.
Vastetoestand KMR (VS KMR) en positronvernietigingsleeftydspektroskopie is
gebruik om die saamgestelde faseskeidingspunt in die entkopolimere te bepaal. Die
spindifffusie data van VS KMR het insig verleen aan die oënskynlik onreëlmatige positrondata by die faseskeidingspunt. In die studie is bewys hoe hierdie twee tegnieke
komplimentêre data kan lewer m.b.t. die vastetoestandmorfologie van hierdie multifase
materiale.
|
360 |
Synthesis and characterization of two novel urethane macromonomers and their methacrylic/urethane graft copolymersAlshuiref, Abubaker 03 1900 (has links)
Thesis (PhD (Chemistry and Polymer Science))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT:
Polymethacrylates are well known adhesives and can carry specific functionality, but have
the disadvantage that their flexible backbones impart limited thermal stability and mechanical
strength. Polyurethanes (PUs) are finding increasing application and use in many industries
due to their advantageous properties, such as a wide range of flexibility combined with
toughness, high chemical resistance and excellent weatherability. PUs do however have
some disadvantages, for instance, PU is considered an expensive polymer, especially when
considered for solvent based adhesives. the focus of this study was to consider a largely
unstudied area of PU chemistry, namely combining PUs with polymethacrylates.
Two types of linear urethane macromers (UMs) UM1 and UM2 were synthesized by the
polyaddition polymerization of 4,4'-methylenediphenyl diisocyanate (MDI) with ethylene
glycol (EG), and MDI with neopentylglycol (NPG), via a pre-polymer method, followed by
termination with 2-hydroxy ethylacrylate (2-HEA) and methanol (MeOH) to yield UMs having
specific urethane chain lengths, and which have to be predominantly monofunctional.
Structural identification of the UMs was verified by MALDI-TOF-MS, FTIR, 13C-NMR and 1HNMR
spectroscopy.Various percentages of the respective UMs (0_55 wt % of methacrylate monomers) were
then incorporated into polymethyl methacrylate (PMMA) and poly n-butyl methacrylate
(PnBMA) backbones via solution free-radical copolymerization. The resulting methyl
methacrylate-g-urethane and n-butyl methacrylate-g-urethane copolymers were
characterized by 1H-NMR,13C-NMR, FTIR, SEC with double detectors (UV and RI), light
scattering, UV-Vis, HPLC, TGA, DSC, DMA and TEM. Weight percentages of UM
incorporated into the methyl methacrylate-g-urethane copolymers were calculated using
FTIR, UV-Vis and 1H-NMR techniques. Phase separation which occurred between the
urethane segment and methacrylate segment in the graft copolymerization products was
investigated by DMA, DSC and TEM analysis.
Microphase separation occurred in all PMMA-g-UM1 and PnBMA-g-UM1 copolymers: two
glass transitions temperatures corresponding to the PMMA or PnBMA and UM1 fractions,
respectively, were observed. On the other hand, DMA and DSC results showed that in most
graft copolymer products the two respective component parts PMMA-g-UM2 or PnBMA-g-
UM2 were compatible, because only one Tg was observed. Two glass transitions occurred
for PMMA or PnBMA and UM2 when the amount of UM was increased to 55 wt % during
copolymerization and microphase separation was evident in DSC, DMA and TEM
measurements. Thermal stability and storage modulus (stiffness) of all the synthesized PMMA-g-urethane
and PnBMA-g-urethane copolymers increased as the concentration of urethane
macromonomer in the copolymerization feed increased, as confirmed in TGA and DMA
results. The surface and adhesive properties of the synthesized graft copolymer were studied
by measuring the static contact angle and peel strength. Adhesion increased as the content
of UMs increased in the graft copolymer. The graft copolymers prepared using a high UM2
feed for both PMMA and PnBMA showed improved in adhesion compared to the pure
methacrylate polymers. The adhesion was better for both leather and for vinyl. / AFRIKAANSE OPSOMMING:
Polimetakrilate is bekende kleefstowwe. Hulle het egter die tekortkoming dat hulle buigbare
ruggraat beperkte termiese en meganiese stabliteit besit. Poliuretane (PUs) word deesdae al
hoe meer gebruik in baie nywerhede as gevolg van hulle baie voordele, insluitend hul wye
buigsaamheid tesame met sterkte, hoë chemiese weerstand en uitstekende weerbaarheid.
PUs het egter ’n paar nadele: hulle is baie duur, veral wanneer hulle gebruik word in
oplosmiddel-gebaseerde kleefstowwe. Die doel van hierdie studie is om die kombinering van
PUs met polimetakrilate te bestudeer, 'n onderwerp wat tot dusver baie min aandag-getrek
het.
Twee tipes liniêre uretaanmakromere (UMs), UM1 en UM2, is gesintetiseer deur
gebruik te maak van poliaddisiepolimerisasie van 4,4'-metileendifeniel diisosianaat (MDI) met
etileenglikol (EG), en MDI met neopentielglikol (NPG), via ‘n prepolimeermetode, gevolg deur
terminering met 2-hidroksiëtielakrilaat (2-HEA) en metanol (MeOH). Die produk hiervan is
UMs met spesifieke kettinglengtes (hoofsaaklik monofunksioneel). Die samestelling van die
UMs is met behulp van die volgende gevorderde analitiese tegnieke bepaal: MALDI-TOFMS,
FTIR, 13C-NMR en 1H-NMR.
Verskillende hoeveelhede van die UMs (0_55 gewIing% metakrilaatmonomere) is dan
in die polimetielmetakrilaat (PMMA) en poli-n-butielmetakrilaat (PnBMA) ruggrate
geïnkorporeer deur middel van oplossing-vryradikaalpolimerisasie. Die samestelling van die
kopolimeerprodukte, metiel-metakrilaat-g-uretaan en n-butiel-metakrilaat-g-uretaan, is met
behulp van die volgende gevorderde analitiese tegnieke bepaal: 1H-NMR, 13C-NMR, FTIR,
SEC met dubbele detektors (UV en RI), ligverstrooiing UV-Vis, HPLC, TGA, DSC, DMA en
TEM. Die hoeveelheid UM geïnkorporeer in die metielmetakrilaat-g-uretaan kopolimere is
bereken deur gebruik te maak van FTIR, UV-Vis en 1H-NMR data. Die faseskeiding wat
plaasgevind het tussen die uretaansegment en die metakrilaatsegment in die produkte van
die entpolimerisasie is met behulp van DMA, DSC en TEM ondersoek.
In alle PMMA-g-UM1 en PnBMA-g-UM1 kopolimere het mikrofaseskeiding
plaasgevind: twee verskillende glasoorgangstemperature vir die PMMA of PnBMA en UM1
fraksies is waargeneem. Hierteenoor het DMA en DSC resultate getoon dat in die meeste
entkopolimeerprodukte (PMMA-g-UM2 of PnBMA-g-UM2) was die twee komponente
verenigbaar, aangesien net een Tg waargeneem is. In die geval van die kopolimere waar die
hoeveelheid UM in die kopolimerisasiereaksies tot 55 gew% verhoog is, is twee
glasoorgangstemperature vir PMMA of PnBMA, en UM2 waargeneem. Mikrofaseskeiding is
met behulp van DSC, DMA en TEM bewys.
Termiese stabiliteit en stoormodulus (styfheid) van alle gesintetiseerde PMMA-g uretaan en PnBMA-g-uretaan kopolimere het toegeneem namate die uretaankonsentrasie in
die kopolimerisasiereaksie toegeneem het soos deur middel van TGA en DMA resultate
bewys is. Die oppervlakte- en kleefeienskappe van die bereide entkopolimere is bestudeer
deur die statiese-kontakhoek en skilkrag te meet. Adhesie het toegeneem namate die UMinhoud
toegeneem het. Die entkopolimere berei met hoë PMMA en PnBMA inhoud het
uiteindelik beter adhesie getoon as die suiwer metakrilaatpolimere. Die adhesie was beter vir
beide leer en viniel.
|
Page generated in 0.0528 seconds