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Synthesis and Interfacial Behavior of Functional Amphiphilic Graft Copolymers Prepared by Ring-opening Metathesis PolymerizationBreitenkamp, Kurt E. 01 February 2009 (has links)
This thesis describes the synthesis and application of a new series of amphiphilic graft copolymers with a hydrophobic polyolefin backbone and pendent hydrophilic poly(ethylene glycol) (PEG) grafts. These copolymers are synthesized by ruthenium benzylidene-catalyzed ring-opening metathesis polymerization (ROMP) of PEG-functionalized cyclic olefin macromonomers to afford polycyclooctene- graft -PEG (PCOE- g -PEG) copolymers with a number of tunable features, such as PEG graft density and length, crystallinity, and amphiphilicity. Macromonomers of this type were prepared first by coupling chemistry using commercially available PEG monomethyl ether derivatives and a carboxylic acid-functionalized cycloctene. In a second approach, macromonomers possessing a variety of PEG lengths were prepared by anionic polymerization of ethylene oxide initiated by cyclooctene alkoxide. This methodology affords a number of benefits compared to coupling chemistry including an expanded PEG molecular weight range, improved hydrolytic stability of the PEG-polycyclooctene linkage, and a reactive hydroxyl end-group functionality for optional attachment of biomolecules and probes. The amphiphilic nature of these graft copolymers was exploited in oil-water interfacial assembly, and the unsaturation present in the polycyclooctene backbone was utilized in covalent cross-linking reactions to afford hollow polymer capsules. In one approach, a bis -cyclooctene PEG derivative was synthesized and co-assembled with PCOE-g-PEG at the oil-water interface. Upon addition of a ruthenium benzylidene catalyst, a cross-linked polymer shell is formed through ring-opening cross-metathesis between the bis -cyclooctene cross-linker and the residual olefins in the graft copolymer. By incorporating a fluorescent-labeled cyclooctene into the graft copolymer, both oil-water interfacial segregation and effective cross-linking were confirmed using confocal laser scanning microscopy (CLSM). In a second approach, reactive functionality capable of chemical cross-linking was incorporated directly into the polymer backbone by synthesis and copolymerization of phenyl azide and acyl hydrazine-functional cyclooctene derivatives. Upon assembly, these reactive polymers were cross-linked by photolysis (in the phenyl azide case) or by addition of glutaraldehyde (in the acyl hydrazine case) to form mechanically robust polymer capsules with tunable degradability ( i.e. non-degradable or pH-dependent degradability). This process permits the preparation of both oil-in-water and water-in-oil capsules, thus enabling the encapsulation of hydrophobic or hydrophilic reagents in the capsule core. Furthermore, the assemblies can be sized from tens of microns to the 150 nm - 1 µm size range by either membrane extrusion or ultrasonication techniques. These novel capsules may be well-suited for a number of controlled release applications, where the transport of encapsulated compounds can be regulated by factors such as cross-link density, hydrolytic stability, and environmental triggers such as changes in pH.
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Synthesis and characterization of urethane-acrylate graft copolymersAlshuiref, Abubaker 12 1900 (has links)
Thesis (MSc (Chemistry and Polymer Science))--University of Stellenbosch, 2006. / 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, excellent weatherability, and very low temperature
cure. PUs do however have some disadvantages, for instance, PU is considered an
expensive polymer, especially when considered for solvent based adhesives. A
motivation for this study was to consider a largely unstudied area of PU chemistry by
combining PUs with polyacrylates. Polyacrylates are well known adhesives and can
carry specific functionality, but have the disadvantage that their flexible backbones
impart limited thermal stability and mechanical strength. In this study PU was
incorporated into acrylates in an effort to obtain acrylate-g-urethanes with good
properties. The mode of incorporation chosen was urethane macromonomers (UMs), a
hardly mentioned substance in literature, yet one deserving investigation.
UMs having different urethane chain lengths (X) were synthesized by the polyaddition
polymerization of toluene diisocyanate (TDI) and ethylene glycol (EG) by the prepolymer
method, which was terminated by 2-hydroxy ethyl methacrylate (HEMA) and
isopropanol. The UMs were characterized by Fourier-transform infrared spectroscopy
(FTIR), proton NMR (1H NMR), carbon NMR (13C NMR), gel permeation chromatography
(GPC), thermogravimetric analysis (TGA) and dynamic mechanical analysis (DMA).
Various percentages of the respective UMs (0-40 wt % according to acrylate monomers)
were then incorporated into methyl methacrylate (MMA) and into normal butyl
methacrylate (n-BMA) backbones via solution free radical copolymerization. The
resulting methyl methacrylate-urethane graft copolymers (PMMA-g-urethane) and
normal butyl methacrylate-urethane graft copolymers (n-PBMA-g-urethane) were
characterized by GPC, 1H NMR and 13C NMR, FTIR, TGA, and DMA. Phase separation
between the urethane segment and acrylate segment in the yield of graft
copolymerization products was investigated by DMA and transmission electron
microscopy (TEM).
As the concentration of the UMs in the free radical copolymerization feed increased,
lower yields of both graft copolymers PMMA-g-urethane and n-PBMA-g-urethane were observed and more UM was incorporated into the PMMA and n-PBMA backbones. It
also was found that the thermal stability of the PMMA-g-urethane and n-PBMA-gurethane
copolymers increased with increasing UM concentration.
DMA results showed that in most graft copolymer products the two respective
component parts of PMMA-g-urethane or n-PBMA-g-urethane were completely
compatible as only one Tg was observed. Two glass transitions, at temperatures of 22.0
and 76.0 oC, corresponding to the n-PBMA and urethane moieties, were observed when
the chain length of the UMs was increased from X=4 to X=32 [the amount of this UM
used in the copolymerization feed was increased to 40%, and microphase separation
was indicated].
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Synthesis and characterization of comb-polymers with controlled structureElhrari, Wael 12 1900 (has links)
Thesis (MSc (Chemistry and Polymer Science))--University of Stellenbosch, 2006. / Synthesis of a series of poly (methylmethacrylate)-graft-poly (styrene) polymer was
carried out via free radical polymerization of methylmethacrylate and polystyrene
macromonomers. The macromonomers were synthesized via living anionic
polymerization techniques. Two series of macromonomers where synthesized with
different polymerizable end group functionalities, by termination with p-vinyl benzyl
chloride and 3-(dimethyl chloro silyl) propyl methacrylate. The branch density was varied
by controlling the composition feed ratio of the macromonomers to comonomer. Liquid
chromatographic techniques were used to fully characterize the chemical composition
and branch distributions of the graft polymer. Liquid chromatography under critical
conditions of adsorption of styrene coupling with Fourier Transform Infrared Spectra was
used to investigate the chemical composition and distribution of the branches in the
graft. Physical properties of the graft copolymers such as Tg and free volume were
determined using differential scanning calorimetry and positron lifetime spectrometry
respectively. The relationship between the chemical composition and the graft
copolymer properties such as Tg and free volume were investigated. The results show
that for long chain macromonomers phase segregation occurs in the graft copolymers. In
the case of shorter chain macromonomers at low content no phase segregation is
observed and the macromonomers have an antiplasticization effect on the graft
polymers.
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RAFT-mediated synthesis of graft copolymers via a thiol-ene addition mechanismStegmann, Jacobus Christiaan 12 1900 (has links)
Thesis (MSc)--University of Stellenbosch, 2007. / ENGLISH ABSTRACT: The main objective of this project was the controlled synthesis of graft copolymers via a
thiol-ene addition mechanism. The Reversible Addition-Fragmentation chain Transfer
(RAFT) process was used in all polymerization reactions with the aim to achieve a
certain degree of control over the molecular weight. Several synthetic steps were
required in order to obtain the final graft copolymer and each step was investigated in
detail.
Firstly, two RAFT agents (cyanovaleric acid dithiobenzoate and dodecyl isobutyric acid
trithiocarbonate) were synthesized to be used in the various polymerization reactions of
styrene and butyl acrylate. This was done successfully and the RAFT agents were used
to synthesize low molecular weight polystyrene branches of the graft copolymer.
Different molecular weights were targeted. It was found that some retardation
phenomena were present especially at high RAFT agent concentrations.
The polystyrene branches that were synthesized contained RAFT end-groups. Various
pathways were explored to modify these RAFT end-groups to form thiol end-groups to
be used in the thiol-ene addition reaction during the grafting process. The use of sodium
methoxide for this purpose proved most successful and no evidence of the formation of
disulfide bridges due to the initially formed thiols was detected.
Allyl methacrylate (AMA) was chosen as monomer to be used for the synthesis of the
polymer backbone because it has two double bonds with different reactivities. For the
first time, RAFT was used to polymerize AMA via the more reactive double bond to
obtain linear poly(allyl methacrylate) (PAMA) chains with pendant double bonds.
However, at higher conversions, gelation occurred and the molecular weight distributions
were uncontrolled. NMR was successfully used to study the tacticity parameters of the
final polymer.
Finally, the synthesis of the graft copolymer, PAMA-g-polystyrene, was carried out by
means of the “grafting onto” approach. The thiol-functionalized polystyrene branches
were covalently attached to the pendant double bonds of the PAMA polymer backbone
via a thiol-ene addition mechanism in the presence of a free radical initiator. A Multi-
Angle Laser Light Scattering (MALLS) detector was utilized in conjunction with Size-
Exclusion Chromatography (SEC) to obtain molecular weight data of the graft
copolymer. The percentage grafting, as determined by 1H-NMR, was low. / AFRIKAANSE OPSOMMING: Die hoofdoel van hierdie projek is die beheerde sintese van ‘n entkopolimeer via ‘n
merkaptaan-een addisiereaksie. Die sogenaamde “Reversible Addition-Fragmentation
chain Transfer” (RAFT) proses is in al die polimerisasiereaksies gebruik met die doel om
‘n mate van beheer oor die molekulêre massa van die polimere te verkry. Verskeie
stappe (waarvan elkeen ten volle ondersoek is) was nodig om die finale entkopolimeer te
verkry.
Eerstens is twee RAFT-agente (sianovaleriaansuur ditiobensoaat en dodekielisobottersuur
tritiokarbonaat) gesintetiseer vir gebruik in verskeie polimerisasiereaksies van stireen en
butielakrilaat. Hierdie stap was suksesvol en die RAFT-agente is toe gebruik vir die
sintese van lae molekulêre massa polistireensytakke vir die entkopolimeer. Die
molekulêre massas van die sytakke is gevarieer en daar is gevind dat vertragings in die
polimerisasiereaksies voorgekom het, veral by hoë konsentrasies van die RAFT-agente.
Die polistireensytakke wat gemaak is, besit almal ‘n RAFT-eindgroep. Verskeie roetes is
bestudeer ten einde die RAFT-eindgroepe tot merkaptaan-eindgroepe te modifiseer om
sodoende tydens ‘n merkaptaan-een addisiereaksie gebruik te word. Die gebruik van
natriummetoksied was hier die suksesvolste en daar was geen teken van die vorming van
disulfiedbrûe as gevolg van die oorspronklik gevormde merkaptane nie.
Allielmetakrilaat (AMA) is gekies as die monomeer wat gebruik sou word vir die sintese
van die polimeerruggraat omdat die monomeer twee dubbelbindings met verskillende
reaktiwiteite besit het. Vir die eerste keer is RAFT gebruik vir die polimerisasie van
AMA via die meer reaktiewe dubbelbinding om lineêre poli(allielmetakrilaat) (PAMA)
kettings met dubbelbindings in die sygroepe te verkry. Gelvorming en onbeheerde
molekulêre massaverspreiding het egter by hoër monomeeromsettings voorgekom. KMR
is susksekvol gebruik om die taktisiteitsparameters van die finale polimeer te bestudeer.
Ten slotte is die sintese van die entkopolimeer, PAMA-g-polistireen, uitgevoer deur die
aanhegting van voorafgevormde sytakke. Die polistireensytakke met die
merkaptaaneindgroepe is kovalent geheg aan die dubbelbindings in die sygroepe van die
PAMA-polimeerruggraat via ‘n merkaptaan-een addisiemeganisme in die
teenwoordigheid van ‘n vrye radikaalinisieerder. ‘n Kombinasie van
gelpermeasiechromatografie en multi-hoeklaserligverstrooiing is gebruik om die
molekulêre massa van die entkopolimeer te bepaal. Die persentasie sytakke soos bepaal
deur 1H-KMR was laag.
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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.
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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.
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Synthesis and characterization of graft and block copolymers using hydroborationBaleg, Abd-Almonam 12 1900 (has links)
Thesis (MSc (Chemistry and Polymer Science))--University of Stellenbosch, 2006. / Graft and block copolymers were synthesized using multifunctional and
monofunctional macroinitiators to produce the copolymers. The process involved
hydroboration of commercially available unsaturated rubbers and chain-end
unsaturated macromonomers with 9-borabicyclo [3.3.1] nonane (9-BBN). The
resulting secondary alkyl 9-BBN moieties in the starting materials were subsequently
exposed to oxygen in the presence of free radical polymerizable monomers to
facilitate the formation of graft and block copolymers.
This research was initiated by first studying the hydroboration of a model compound,
2-hexene, in order to determine the optimal conditions for the graft reactions. The
model compound was subsequently used as a macroinitiator to initiate the
polymerization of methylmethacrylate (MMA). The same borane chemistry was
extended to the synthesis of polystyrene (PS) block copolymers. Chain-end
unsaturated PS macromonomers, synthesized by anionic polymerization, were
effectively hydroborated and then polymerized to produce PS-b-PMMA block
copolymers.
The synthesis of polyolefin graft copolymers was subsequently achieved by
hydroboration. Several commercial rubbers with different levels of unsaturated
segments were efficiently grafted with vinyl monomers MMA and styrene (St)
following the “graft from” approach. The grafted reactions were carried out under
various reaction conditions to determine the effect of the following factors:
concentration of oxygen, amount of borane and monomer concentration. By
controlling these factors, different graft densities were achieved with high graft
efficiencies. All reactions produced mixed products including unreacted
(non-functional) macroinitiator, homopolymer, graft copolymer and in case of the
highly unsaturated polymer a crosslinked gel.
Finally, the chemical compositions as well as the molar mass distribution of the graft
copolymers were fully characterized by different chromatographic techniques.
1H-NMR and FTIR were also used to confirm the structure of these copolymers.
Gradient HPLC was developed and extensively used to characterize the graft
copolymers.
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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.
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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.
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40 |
Free volume of electrospun organic-inorganic copolymersBasson, Neil 04 1900 (has links)
Thesis (MSc)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: Two series of amphiphilic, organic-inorganic graft copolymers of poly(methyl
methacrylate) and poly(dimethylsiloxane) (PMMA-graft-PDMS), as well as
poly(acrylonitrile) and poly(dimethylsiloxane) (PAN-graft-PDMS), were synthesized
via conventional free radical copolymerization using the ―grafting through‖ technique.
In both series the PDMS macromonomer content varied from 5 wt.% - 25 wt.% and
different graft lengths of 1000 g/mol and 5000 g/mol were used. A gradient elution
profile was developed to monitor the removal of the unreacted PDMS
macromonomer using hexane extraction. In the case of the PAN copolymer series,
the gradient profile showed that as the PDMS content in the feed increased, more
PAN-graft-PDMS molecules formed relative to homopolymer PAN. In the case of the
PMMA copolymer series, mostly PMMA-graft-PDMS molecules were formed as the
PDMS content in the feed increased. In the case of the PAN-graft-PDMS series, the
PDMS content affected the crystallization behaviour of the PAN segments and lead
to a decrease in crystallinity across the composition range as the PDMS content
increased. It is shown that the synthesized graft copolymers can be electrospun to
produce continuous nanofibers. The effects of polymer solution concentration,
copolymer composition and tip-to-collector distance on the fiber morphology are
discussed. The rapid stretching of the polymer jet, as well as the rapid solvent
evaporation during the electrospinning process, resulted in highly complex nonequilibrium
morphologies in the case of the electrospun PAN-graft-PDMS
copolymers. The crystallization behaviour of the electrospun fibers of PAN-graft-
PDMS was shown to be different from the unprocessed precursor material. Surface
oxidised MWCNTs were successfully incorporated and well dispersed into the graft
copolymers via the electrospinning process to produce nanocomposite nanofibers. In
the case of the PAN-graft-PDMS copolymer series, the presence of MWCNTs in the
nanocomposite nanofibers enhanced the overall degree of crystallinity when
compared to the unfilled nanofibers. For the first time positron annihilation lifetime
spectroscopy (PALS) analysis was performed on the various complex graft
copolymer compositions and their electrospun fiber analogues, as well as
nanocomposites, to investigate the free volume properties of the various materials. The results revealed that there are two distinct ortho-positronium (o-Ps) lifetime
parameters for these complex multiphased materials. The shorter lived lifetime -3
was attributed to the o-Ps annihilation in the amorphous regions of the crystalline
PAN phase in the PAN-graft-PDMS copolymer series, as well as to the o-Ps
annihilation in the amorphous PMMA phase in the case of the PMMA-graft-PDMS
copolymer series. The longer lived lifetime -4 was attributed to the o-Ps annihilation
in the more amorphous PDMS phase. In the case of the PMMA series the relative
fractional free volume was influenced by the graft lengths, where the 5000 g/mol
series showed a larger increase in fractional free volume relative to the shorter 1000
g/mol series. The effects of the tip-to-collector distance during electrospinning, as
well as the inclusion of MWCNTs, on the free volume properties are also discussed.
It is demonstrated how positron annihilation lifetime spectroscopy can provide
valuable and unique information on the internal structure and morphology of the
electrospun nanofibers. / AFRIKAANSE OPSOMMING: Twee reekse amfifiliese, organies-anorganiese entkopolimere van
poli(metielmetakrilaat) en poli(dimetielsiloksaan) (PMMA-ent-PDMS), asook
poli(akrilonitriel) en poli(dimetielsiloksaan) (PAN-ent-PDMS), is gesintetiseer deur
konvensionele vrye-radikaalkopolimerisasie. Die PDMS makromonomeerinhoud het
gewissel tussen 5 wt.% - 25 wt.% in albei reekse en sykettinglengtes van 1000 g/mol
en 5000 g/mol is gebruik. `n Gradient-eluasieprofiel is opgestel om die verwydering
van ongereageerde PDMS makromonomeer d.m.v. heksaanekstraksie te monitor. In
die PAN kopolimeer reeks het die gradient-eluasieprofiel gewys dat meer PAN-ent-
PDMS molekules vorm relatief tot die PAN homopolimeer sodra meer PDMS
bygevoeg word. In die PMMA kopolimeer reeks het meer PMMA-ent-PDMS
molekules gevorm sodra meer PDMS toegevoeg is. In die geval van die PAN-ent-
PDMS reeks, het die PDMS die kristallisasiegedrag van die PAN segmente
geaffekteer en `n afname in die totale kristalliniteit veroorsaak soos die PDMS
inhoud vermeerder het. Daar word bewys dat die gesintetiseerde entkopolimere geelektrospin
kan word om nanovesels te vorm. Die effek van
polimeeroplossingskonsentrasie, kopolimeersamestelling en punt-tot-versamelaarafstand
op die nanoveselmorfologie word bespreek. Die vinnige strekking van die
polimeerjet sowel as die vinnige verdamping van die oplosmiddel gedurende die
elektrospinproses het gelei tot hoogs komplekse nie-ekwilibrium morfologieë in die
geval van die ge-elektrospinde PAN-ent-PDMS kopolimere. Die kristallisasiegedrag
van die nanovesels van PAN-ent-PDMS het verskil van die onverwerkte voorloper
materiaal. Oppervlakgeoksideerde MWCNTs is suksevol geïnkorporeer en versprei
in die entkopolimere d.m.v. die elektrospinproses om nanosaamgestelde nanovesels
te vorm. Die teenwoordigheid van MWCNTs in die nanosaamgestelde nanovesels in
die PAN-ent-PDMS kopolimeerreeks het gelei tot `n verbetering in die algehele
kristalliniteit in vergelyking met die nanovesels sonder MWCNTs. Positronvernietigingsleeftyd-
spektroskopie (PALS) is vir die eerste keer gebruik om die vrye
volume van verskillende kompleks entkopolimeersamestellings, hul ge-elektrospinde
nanovesels sowel as nanosaamgestelde nanovesels te bestudeer. Die resultate het
getoon dat daar twee verskillende orto-positronium (o-Ps) leeftydparameters vir hierdie komplekse multifase materiale bestaan. Die korter leeftydparameter -3 word
toegeskryf aan die o-Ps vernietiging in die amorfe areas van die kristallyne PAN fase
in die PAN-ent-PDMS kopolimeerreeks, sowel as die o-Ps vernietiging in die amorfe
PMMA fase in die PMMA-ent-PDMS kopolimeerreeks. Die langer leeftydparameter
-4 word toegeskryf aan die o-Ps vernietiging in die amorfe PDMS fase. Die relatief
fraksionele vrye volume van die PMMA reeks is deur die verskillende syketting
lengtes beïnvloed. Die 5000 g/mol syketting het `n groter toename in fraksionele vrye
volume veroorsaak relatief tot die korter 1000 g/mol syketting. Die effek van die punttot-
versamelaar-afstand tydens die elektrospinproses op die vrye volume
eienskappe, sowel as die insluiting van MWCNTs, word bespreek. Daar word
aangedui hoe positron-vernietigingsleeftyd-spektroskopie waardevolle en unieke
inligting kan verskaf oor die interne struktuur en morfologie van die nanovesels.
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