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Synthesis and characterization of tailored polyurethane coatingsSeboa, Sharrief 12 1900 (has links)
Thesis (DSc (Chemistry and Polymer Science))--University of Stellenbosch, 2005. / Aqueous polyurethane (PU) dispersions were synthesized for use in paper coatings. These
PUs contained a polyester polyol soft segment (content of between 65 to 75%) and a
urethane hard segment (content of between 30 to 35%). Triethylamine (TEA) was used as
the neutralizing agent. The polyester polyol segment consisted of neopentyl glycol (NPG),
adipic acid, 1,4-cyclohexane dicarboxylic acid (1,4-CHDCA) and 2-phosphonobutane-
1,2,4-tricarboxylic acid (PBTCA), while the urethane hard segment consisted of toluene
diisocyanate (TDI), dimethylolproponic acid (DMPA) and ethylene glycol (EG) as a chain
extender for increasing the hard segment content.
Waxes and fillers were incorporated into the PU coating mixtures to investigate their effect on
the barrier properties of the PU. Two types of fillers were used: nano-fillers and micro-fillers.
The nano-fillers used included the Cloisite nano-clays NC15A, NC93A and NC30B, and the
micro-fillers used included talc, kaolin clay and barium sulfate.
Two different polyester polyols were synthesized: one containing a phosphate and the other
containing no phosphate. The polyols were characterized in terms of their acid value,
hydroxyl value and molecular mass. The PUs synthesized from the polyol containing no
phosphate showed unfavourable barrier properties compared to results achieved with the
phosphate-containing PU.
The PU dispersions were applied to paperboard, and then dried at a maximum temperature
of 130oC for 15 to 60 seconds, depending on the coating volume. The PU-coated paperboard
was characterized primarily by determining the moisture vapour transmission rate (MVTR),
and by scanning electron microscopy (SEM).
PU films (stand alone, not supported by paper) were prepared by heating the concurrent PU
dispersion in Teflon holders over three different temperature stages (60, 90 and 120oC) for
about 2 days. The dried films were then characterized by thermogravimetric analysis (TGA),
differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), Fourier
transform infrared (FTIR) and nuclear magnetic resonance (NMR) spectroscopy.
The PU coatings showed self-assembly properties, which were affected primarily by the ionic
content (comprising of DMPA, PBTCA and excess TEA) and emulsion viscosity. These
self-assembly properties were analyzed by static contact angle (SCA) and MVTR measurements. It was found that the final coating properties were affected by the
self-assembly mechanism of the PU.
Generally, the phosphated PU coatings had lower MVTR values than the non-phosphated
PU coatings. SEM analysis showed that the phosphated PU coatings had no pinholes, while
the non-phosphated PU coatings had pinholes. DMA analysis showed that the phosphated
PUs had higher Tg values than the non-phosphated PUs. Further, the inclusion of the
phosphate monomer increased the emulsion stability and the compatibility between the hard
and soft segments of the PU.
Also, the exfoliated PU nanocomposites at 1% filler loading gave much better MVTR results
compared to the PU microcomposites. It also rendered the coating to be non-blocking, with
minimal change in MVTR.
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Novel analytical approaches for studying degradation in polypropylene and propylene-1-pentene copolymersDe Goede, Stefan 03 1900 (has links)
Thesis (DSc (Chemistry and Polymer Science))--University of Stellenbosch, 2006. / Commercial polyolefins degrade under the influence of light, heat, chemical and mechanical factors. They are therefore stabilised to ensure that they maintain performance characteristics during their service life. Degradation results in changes in the molar mass, molar mass distribution, chemical composition and chemical composition distribution. Classical analytical techniques only provide averaged values of these properties. Much information is available in the open literature on the changes in molar mass, molar mass distribution and chemical composition of polypropylene upon degradation, but no information was available on the changes in chemical composition distribution (CCD) during degradation.
This study describes the use of the following analytical techniques to study this: temperature rising elution fractionation (TREF), crystallisation analysis fractionation (CRYSTAF) and coupled size exclusion chromatography-Fourier transform infrared analysis (SEC-FTIR). The CRYSTAF results complimented those obtained by classical techniques: there was a broadening of the crystallisation peak (CCD), an increase in the soluble fraction and a decrease in crystallisation temperatures. SEC-FTIR analysis showed that most of the degraded products were concentrated in the low molar mass regions. TREF analysis was used to separate a degraded sample into fractions of different degrees of degradation. It was then possible to study the spatial heterogeneity in a thick, degraded polypropylene sample using SEC, FTIR and CRYSTAF.
The degradation behaviour of selected Sasol propylene-1-pentene random copolymers was investigated. CRYSTAF, SEC-FTIR and TREF analyses provided information on the thermo-oxidative degradation behaviour differences between unstabilised polypropylene homopolymers and these propylene-1-pentene copolymers. It was found that the pentene copolymers degraded significantly faster compared to the homopolymers, even at low levels of pentene (< 3%). The reduction in stability was virtually linear with an increase in pentene content (up to 8 mol% pentene), indicating that higher levels of primary stabilisers are needed to ensure similar life spans for the Sasol propylene-1-pentene copolymers. The extrusion stability of the propylene-1-pentene copolymers was, however, similar to that of the polypropylene homopolymers, indicating that similar processing stabiliser packages may be used.
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Structure/property relationships of commercial propylene/1-pentene random copolymersLutz, Marietjie 03 1900 (has links)
Thesis (PhD (Chemistry and Polymer Science))--University of Stellenbosch, 2006. / Propylene/1-pentene random copolymers are a relatively new family of random copolymers being prepared by Sasol Polymers and reveals high impact strength, good tensile properties, excellent optical properties, good rheological properties and a large pool of processing possibilities. These commercial copolymers are being prepared with stereospecific heterogeneous Ziegler-Natta catalytic systems containing multiple active sites and therefore producing copolymers with a varying degree of stereoregularity. Two different groups of propylene/1-pentene random copolymers were received by Sasol Polymers and investigated in this project.
The first group (Group 1, Polymers A - F) consisted of six totally different batches of commercial propylene/1-pentene copolymers which were produced by different catalyst systems. All had different melt flow indices (MFIs) and different 1-pentene contents and all of the copolymers, except for one, were nucleated. The second group (Group 2, Polymers G - J) were produced by the same catalyst, but with varying donor:catalyst ratios and also differing in their 1-pentene content. Investigation of the Group 1 copolymers was used in order to construct a “molecular toolbox” which was then used to study the Group 2 copolymers.
The original commercial copolymers were all studied by various analytical techniques: high-temperature carbon thirteen nuclear magnetic resonance spectroscopy (13C-NMR), high-temperature gel permeation chromatoghraphy (HT-GPC), crystallization analysis fractionation (CRYSTAF), differential scanning calorimetry (DSC), wide angle X-ray diffraction (WAXD) and positron annihilation lifetime spectroscopy (PALS).
The random copolymers were all fractionated by preparative TREF and the fractions analyzed utilizing the following analytical techniques: 13C-NMR, HT-GPC, CRYSTAF and DSC. The results of these analyses were used to investigate inter alia the distribution of 1-pentene in the copolymers.
In order to investigate the low molecular weight material of the copolymers, which were part of the room temperature fraction during TREF, solvent extractions were carried out using different solvents and different extraction techniques. A complete structural analysis study was carried out on the extracts. The percentages of xylene-solubles were also determined during the quantitative xylene extraction study of the copolymers. Characterization of the xylene non-soluble material was carried out using 13C-NMR, HT-GPC, CRYSTAF, DSC and WAXD in order to compare the properties of the unextracted copolymers with the material after removal of the xylene soluble fraction. Positron annihilation lifetime spectroscopy (PALS) was used as an alternative investigation method for the Group 1 copolymers and their XNS fractions in order to determine what type of information this novel analytical method could generate and how the results compared with those of previous PALS studies on poly-olefins.
A new fractionation technique, preparative solution fractionation (SF), was developed and evaluated. The commercial propylene/1-pentene copolymers were fractionated using this novel technique, the fractions were analyzed by 13C-NMR, HT-GPC, CRYSTAF and DSC and the results were compared with previously existing fractionation methods, namely TREF and CRYSTAF.
A final study was done on the random copolymers by blending one of the commercial Ziegler-Natta catalyzed propylene/1-pentene copolymers with a tailored, low 1-pentene content, metallocene propylene/1-pentene copolymer in different ratios. The blends were analyzed by molecular weight, thermal and crystal phase analysis in order to investigate the effect of the tailored, highly isotactic propylene/1-pentene copolymer on the properties the commercial random copolymers.
Throughout the project the influence of the 1-pentene as well as the donor:catalyst ratio on the copolymers was investigated. This study, in its entirety, therefore allow a better understanding of the effects that the commercial, heterogeneous, transition metal catalysts have on the make up of the copolymers and, by extension, the ultimate properties of the materials.
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The structure-property relationships of polyolefinsHarding, Gareth 03 1900 (has links)
Thesis (PhD (Chemistry and Polymer Science))--University of Stellenbosch, 2009 / Polypropylene is an extremely versatile material and has a broad spectrum of
applications due to the variations in properties which are possible with this material. The
variations in the properties of the material are governed by the microstructure of the chains
constituting the polymer. The microstructure varies according to the production methods, i.e.
the polymerisation conditions. Varying the manner in which the polymer is produced
therefore changes the properties of the material allowing the polymers’ use for different
applications. The most important factor affecting the way in which the polymers are produced
is the nature of the active sites on the catalyst. Changing the chemical environment of the
active sites changes the way in which the polymerisation is controlled and greatly affects the
types of chains produced and thus polymer properties.
The study examines the structure-property relationships of polyolefins with specific
focus on the polypropylene homopolymer. The temperature rising elution fractionation
(TREF) technique is used extensively in order to isolate specific fractions of the polymer. The
importance of specific TREF fractions is investigated via a two pronged investigative
methodology. On the one hand specific TREF fractions are removed from a sample, allowing
the analysis of the properties of the material without that specific fraction, thereby revealing
the influence which the fraction in question has on the properties. The other branch of the
study investigates the chemical modification of the active sites of a Ziegler-Natta catalyst so
as to be able to modify the properties of the polymer in the reactor, in a similar manner to
physically removing fractions. The techniques are related and it was discovered that the
amount of the fractions of the polymer, found to be important using the one technique, also
turned out to be important using the other method.
Initial method development work utilised a polypropylene-1-pentene copolymer since
the molecular heterogeneity of this material is such that large differences are observed upon
removal of fractions. The technique was then applied to a Ziegler-Natta catalysed
polypropylene homopolymer. Each TREF fraction is successively removed and the residual
material analysed. Specific TREF fractions were found to play a significant role in
determining the polymer properties since there was a drastic reduction in properties upon
removal of these fractions.
The polymerisation of propylene was also performed at a variety of conditions in
order to investigate different ways in which the catalyst system could be modified. Specific
reaction conditions were chosen for in-depth analysis and structure-property correlation. The
chemical modification of the active sites was accomplished via the introduction of an external Lewis base (electron donor) to the polymerisation system, and also by varying the external
donor/catalyst ratio used. Two different external donors were used during the study namely
Diphenyl-dimethoxysilane (DPDMS) and methyl-phenyl-dimethoxysilane (MPDMS). It is
observed that there are definite links between the amounts of specific fractions present in the
polymer and the polymer properties, as observed via both the physical removal of fractions
and the chemical modification of active sites.
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New synthetic and characterization strategies for polyolefinsLuruli, Nyambeni 03 1900 (has links)
Thesis (PhD)--University of Stellenbosch, 2006. / ENGLISH ABSTRACT: Metalloxycarbene complexes [(CO)5M1=O(R)M2(Cl)L2] (M1 = Cr , W; M2 = Zr, Hf; L =
Cp, Cp*) were synthesized from the reaction between anionic Fischer-type carbene
complex salts [(CO)5M1=C(O)R][NEt4] and metallocene chlorides. The molecular and
crystal structures of [(CO)5W=C(Me)OZr(Cp)2Cl], [(CO)5Cr=C(Me)OZr(Cp)2Cl] and
[(CO)5W=C(Ph)OHf(Cl)Cp2] determined by X-ray methods, show a short Ccarbene-O and
relatively long O-Zr and O-Hf separations. Metalloxycarbene complexes in the presence
of MAO are active catalysts for homo- and copolymerization of -olefins and produce
polymers with heterogeneous properties. 1-Pentene oligomers, homopolymers of ethylene
and ethylene/1-pentene copolymers were successfully synthesized using
metalloxycarbenes/MAO and the results obtained were critically compared with those
synthesized with metallocene/MAO catalysts. The GC and GPC show that 1-pentene
oligomers produced with both metalloxycarbenes and metallocenes catalysts range from
simple dimers to more complicated high molecular weight (2 600 g/mol) products. The
properties of polyethylene and ethylene/1-pentene copolymers were evaluated by, among
others, GPC, SEC-FTIR, preparative molecular weight fractionation and HPer DSC.
Generally the polymers obtained using metalloxycarbene/MAO catalysts have broad and
bimodal molecular weight distributions. The copolymers have higher concentration of 1-
pentene in the lower molecular weight fraction than those produced with metallocene/MAO as shown by SEC-FTIR. Consequently, HPer DSC shows a decrease
of melting and crystallization temperature towards the low molecular weight fractions. / AFRIKAANSE OPSOMMING: Metaaloksikarbeenkomplekse [(CO)5M1=C(R)OM2(Cl)L2] (M1 = Cr , W; M2 = Zr, Hf; L
= Cp, Cp*] is gesintetiseer in die reaksie tussen anioniese Fischer-tipe karbeenkomplekssoute,
[(CO)5M1=C(O)R][NEt4], en metalloseen dichloriedes. Die molekulêre- en
kristalstrukture van [(CO)5W=C(Me)OZr(Cp)2Cl], [(CO)5Cr=C(Me)OZr(Cp)2Cl] en
[(CO)5W=C(Ph)OHf(Cl)Cp2] bepaal deur X-straalkristallografiese metodes, toon die
aanwesigheid van kort Ckarbeen-O- en relatief lang O-Zr- en O-Hf-bindings.
Metaaloksikarbeenkomplekse, in die aanwesigheid van MAO, is aktiewe katalisatore vir
die homo- en ko-polimerisering van α-olefiene en is verantwoordelik vir die vorming van
polimere met heterogene eienskappe. 1-Penteen oligomere, homopolimere van etileen en
etileen/1-penteen ko-polimere is suksesvol gesintetiseer met
metaaloksikarbeenkomplekse/MAO en die resultate sodoende verkry, is krities vergelyk
met produkte gesintetiseer vanuit metalloseen/MAO prekatalisatore.
Die GC en GPC resultate toon dat die 1-penteen oligomere, geproduseer met beide
metaaloksikarbeenkomplekse en metallosene, kan wissel van eenvoudige dimere tot meer
komplekse, hoë molekulêre massa (2 600g/mol) produkte. Die polietileen en etileen/1-
penteen ko-polimere is gekarakteriseer deur onder andere gevorderde, GPC, SEC-FTIR,
preparatiewe molekulêre massa fraksionering en HPer DSC. In die algemeen het die
polimere verkry met metaaloksikarbeen/MAO katalisatore, breë en bimodale molekulêre
massaverspreidings. Die ko-polimere bevat hoër konsentrasies van 1-penteen in die lae
molekulêre massa fraksie in vergelyking met dié gevorm vanuit metalloseen/MAO–gekataliseerde mengsels, soos aangedui deur SEC-FTIR-analise. HperDSC wys 'n
verlaging in smelt- en kristallisasietemperature in die laer molekulêre massa fraksies.
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Synthesis, polymerisation and characterisation of a novel olefin-modified acrylate monomer, 1-methyl-1-propyl-hexel acrylateMange, Siyabonga 03 1900 (has links)
Thesis (PhD)--Stellenbosch University, 2005. / ENGLISH ABSTRACT: Finding use for byproducts from the chemical industry holds many advantages for a
country's economy. Synthesis of new monomers from such byproducts adds value
to otherwise otherwise low-value material.
The synthesis of a new olefin-modified acrylate monomer, 1-methyl-1-propyl-hexyl
acrylate (1-MPHA), derived from 1-pentene, is reported. Homopolymerisation of the
monomer 1-MPHA was carried out in both benzene and in toluene. The products of
full-conversion of the homopolymer poly-(1-MPHA) were characterised by GPC,
NMR, TGA and DMA. Kinetic studies of the homopolymerisation process of 1-
MPHAwere also undertaken.
The monomer 1-methyl-1-propyl-hexyl acrylate (1-MPHA) was copolymerised with
methyl methacrylate (MMA). Samples obtained from full conversion
copolymerisations at various 1-MPHAIMMAfeed ratios were characterised by GPC,
NMR, TGA and DMA. Reactivity ratios of the two monomers were obtained from in
situ 1H NMR kinetic studies. 1-MPHA was also copolymerised with vinyl acetate
(VAc). Samples obtained from full conversion copolymerisation with a 1-MPHA
content ranging from 2 to 16 wt% were characterised by GPC, NMR, TGA and DMA.
The solubility parameter and the hydrophobicity of the VAc/1-MPHA copolymers
were also determined. Reactivity ratios of the two monomers were obtained from in
situ 1HNMR kinetic studies.
Further copolymerisation studies with styrene and glycidyl methacrylate as
comonomers were undertaken. The chemical analysis and thermogravimetric
analysis of the copolymers are reported.
In conclusion, the use of 1-methyl-1-propyl-hexyl acrylate as a comonomer results in a
reduction in the glass transition temperature, better thermal stability, increased
hydrophobicity with an insignificant loss in stiffness of the copolymers. These
properties are due to the long and branched chain structure of the 1-MPHA monomer. / AFRIKAANSE OPSOMMING: Gebruik van byprodukte van die chemiese nywerheid hou groot voordele in vir
die land se ekonomie. Sintese van nuwe monomere vanuit sulke byprodukte
dra by tot waardetoevoeging tot andersins lae-waarde byprodukte.
Die sintese van 'n nuwe olefien-gewysigde akrilaatmonomeer afkomstig van
1-penteen, naamlik 1-metiel-1-propiel-heksielakrilaat (1-MPHA), word hier
beskryf. Homopolimerisasie van die monomeer 1-MPHA is uitgevoer in beide
benseen en tolueen. Die produkte van die volledige omskakeling van die
homopolimeer is met behulp van GPC, KMR, TGA en DMA gekarakteriseer.
Die reaksiekinetika van die homopolimerisasie van 1-MPHA is ook ondersoek.
Die monomeer 1-MPHA is met metielmetakrilaat (MMA) gekopolimeriseer.
Monsters van die volledig omgeskakelde kopolimere met verskeie 1-
MPHNMMA voerverhoudings is m.b.v. GPC, KMR,' TGA en DMA
gekarakteriseer. Die reaktiwiteitsverhoudings van die twee monomere is vanaf
1HKMR-studies bepaat.
1-MPHA is ook met vinielasetaat (VAc) gekopolimeriseer. Monsters van die
produk van die volledige kopolimerisasie met 1-MPHA , met 'n inhoud van 2-
16 massa 0/0, is ook m.b.v. GPC, KMR, TGA en DMA gekarakteriseer. Die 1-
MPHA het die hidrofobisiteit van VAc/1-MPHA aansienlik verhoog. Die
reaktiwiteitsverhoudings van die twee monomere is vanaf in situ 1H KMRstudies
bepaal.
Verdere kopolimerisasiestudies met stireen en glisidielmetakrilaat as komonomere
is onderneem. Chemiese- en termogravimetriese analises van die
kopolimere is gedoen en gerapporteer.
Ter afsluiting, die gebruik van 1-metiel-1-propiel-heksielakrilaat as komonomeer
het 'n verlaging in die glasoorgangstemperatuur, verhoogde
termiesestabiliteit, verhoogde hidrofobisiteit, en 'n klein verlies in die
stewigheid (Eng. stiffness) van die kopolimeer tot gevolg. Hierdie eienskappe is as gevolg van die lang, vertakte kettingstruktuur van die 1-MPHA
monomeer.
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Directed synthesis of polymer mesostructuresFaul, C. F. J. (Charles Frederick James) 12 1900 (has links)
Thesis (PhD)--Stellenbosch University, 2000. / ENGLISH ABSTRACT: The objective of this research was to produce discrete, nano-shaped polymeric structures on the
same length scale as, or one to one copies of, templates, deformable templates or structure-directing
hosts.
Polymerisation of hydrophobic organic monomers in high concentration surfactant solutions, leads
to the formation of shaped particles (rod-like, plank-like and ribbon-like particles) in the
micrometer size range. The origin of these regularly shaped particles was investigated. It is
proposed that they were not polymeric in nature, but formed by the crystallisation of the surfactant
in the presence of electrolytes and ethanol as solvent. The polymeric particles that were formed
were found to be of spherical shape, and no directing of the shape was detected.
Mesostructured hosts were then investigated for their possible use as structure-directing agents. A
series of polyelectrolyte-surfactant complexes of polydiallylammonium chloride with sodium
sulphate surfactants (ranging from C10 to C16) were synthesised and characterised in terms of their
thermal, mechanical and structural properties. The complex of polydiallylammonium chloride and
sodium dodecyl sulphate was selected as an appropriate self-assembled model system for
investigations into the structure-directing properties of these new materials.
The polymerisation of hydrophobic organic monomers, such as styrene and the di-functional
monomer m-diisopropenylbenzene (m-DIB), within the above mesoscopically structured
polyelectrolyte-surfactant complex as host, lead to the formation of unconventionally shaped
polymeric particles. The influence of the presence of monomers and guest polymers on the phase
morphology of the host was investigated by small angle X-ray analyses (SAXS) and dynamic
mechanical analyses (DMA). SAXS analyses showed that these new, stable hosts can hold up to 17
% guest polymer before phase disruption is encountered. These findings were supported by
changes in the mechanical properties, as determined by DMA. The transmission electron
microscopy (TEM) images of particles obtained after polymerisation showed very clearly that the
poly-(m-DIB) did not form a continuous copy of the 3D hexagonal structure of the host, but rather
colloidal copies of a part of the host structure that swelled the most. The shapes of the polymer
mesostructures were dictated by the morphology of the phase of the structure-directing host, to produce nanosized wires (dimensions 4 by 100 nm), cigar-shaped particles (dimensions 8 by 50 nm)
and fibrillar bent shapes (larger than 200 nm), as revealed by TEM.
According to literature these are the first shaped, polymer nano-particles produced in a soft, selfassembled,
organic templating host. / AFRIKAANSE OPSOMMING: Die doel van hierdie navorsing was om diskrete, nano-gevormde polimeriese partikels van dieselfde
lengteskaal as, of direkte een tot een kopië van, 'n templaat, 'n vervormbare of struktuur-rigtende
gasheersisteem te produseer.
Die polimerisasie van hidrofobiese organiese monomere in seep oplossings van hoë konsentrasie,
het gelei tot die produksie van gevormde partikels. Die oorsprong van hierdie partikels is
ondersoek. Dit word voorgestel dat die partikels nie polimeries van aard is nie, maar gevorm is
deur die kristallisasie van die seep in die teenwoordigheid van elekotroliete en etanol as
oplosmiddel. Die polimeriese partikels wat wel geproduseer is, was sferies in vorm, en geen
rigtende invloed op die vorm van die partikels is waargeneem nie.
Meso-gestruktureerde gasheersisteme is ook ondersoek vir moontlike gebruik as struktuur-rigtende
agente. 'n Reeks poliëlektroliet-seep komplekse van polidiallielammoniumchloried en
natriumsulfaat sepe (van C10 tot C16) is gesintetiseer en gekarakteriseer in terme van hul termiese,
meganiese en strukturele eienskappe. Die kompleks van polidiallielammoniumchloried en natrium
dodekielsulfaat is gekies as 'n toepaslike self-organiserende modelsisteem vir die ondersoeke na die
struktuur-rigtende eienskappe van hierdie nuwe materiale.
Polimerisasie van hidrofobiese organiese monomere, soos byvoorbeeld stireen en die di-funksionele
monomeer m-di-isopropenielbenseen (m-DIB), in hierdie mesoskopies-gestruktureerde
poliëlektroliet-seep kompleks, het gelei tot die vorming van nie-konvensionele gevormde
polimeriese partikels. Die invloed van die teenwoordigheid van monomere en gaspolimere op die
fasemorfologie van die gasheersisteem is ondersoek d.m.v. kleinhoek X-straal diffraksie (Eng.
SAXS) en dinamiese meganiese analise (DMA). SAXS analises het aangetoon dat hierdie nuwe,
stabiele gasheersisteem tot 17 % gaspolimeer kan inkorporeer voordat fasevernietiging plaasvind.
Hierdie resultate is verder ondersteun deur veranderinge in die meganiese eienskappe soos
waargeneem deur DMA. Transmissie elektronmikroskopie (TEM) afbeeldinge van partikels
geïsoleer na polimerisasie het baie duidelik gewys dat, in die geval van poli-(m-DIB), die
gaspolimeer nie 'n kontinue kopie van die drie dimensionele heksagonale struktuur van die
gasheersisteem produseer nie. Daar word eerder 'kolloïdale kopieë' van dele van die
gasheersisteem wat die meeste swel gevorm. Die vorms van die polimeer mesostrukture word dus
bepaal deur die morfologie van die fase van die struktuur-rigtende gasheer, om nanogrootte draadjies (dimensies 4 x 100 nm), sigaarvormige partikels (8 x 50 nm) en fibrillêre gebuigde vorms
(groter as 200 nm) te vorm, soos waargeneem met TEM.
Volgens die literatuur is hierdie die eerste geval van gevormde polimeer nanopartikels geproduseer
in 'n self-organiserende templaat gasheersisteem.
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Ethylene and propylene copolymers utilizing Fishcer-Tropsch 1-olefinsJoubert, D. J. (Dawid Johannes) 12 1900 (has links)
Thesis (PhD)--Stellenbosch University, 2000. / ENGLISH ABSTRACT: From the Sasol Fischer- Tropsch process, a variety of different a-olefins are produced.
Sasol recently started presenting these a-olefins to polymer producers. To
demonstrate the application possibilities of these a-olefins as comonomers for
ethylene and propylene polymerization, it was necessary to first synthesize catalysts
having a combination of high activity and good comonomer incorporation, and in the
case of propylene copolymers, also sufficient stereospecificities.
Different methods to produce catalysts conforming to these requirements were
investigated and it was found that catalysts produced from a MgCb-support activated
by a combination of chemical and mechanical means produced suitable catalysts. The
amount of alcohol used during the support activation step and the time allowed for
alkylation of the active centers were important. No clear correlation between total
titanium content and activity was observed. The degree to which active sites are
protected was evaluated from the amount of comonomer present in the final copolymer
based on the amount added to the reaction. Cyclopentadiene was used to selectively
deactivate the unprotected active sites to determine the ratio between protected and
"open" active sites. High activity catalysts are not suitable for gas-phase
copolymerization and were consequently "diluted" by dispersion in a pre-formed
polymer powder and by prepolymerization. Catalyst activity based on titanium
content was substantially decreased, but comonomer incorporation was not.
Catalysts for producing crystalline polypropylene require the presence of both an
internal and external electron donor. It was shown that isotacticity increased linearly
with an increase in external modifier at the expense of catalyst activity and that a
double treatment of the support or catalyst before the final TiCl4 fixation was more
effective at increasing stereospecificity. The less stereospecific sites are more capable of accepting bulky comonomers in the coordination complex and thus by decreasing
the amount of less-stereospecific active sites, the overall capability of the catalyst to
incorporate comonomer was decreased.
Comonomer sequence distributions and average lamellar thicknesses of different
ethylene / a-olefin copolymers were calculated from CH2 dyad concentrations
determined by I3C NMR spectroscopy. Ethylene sequences in the I-butene
containing copolymers are generally longer than those where a higher a-olefin was
used as comonomer which indicates that a more random comonomer distribution is
obtained when the higher u-olefins are used. It was shown that an inverse
relationship exists between branch size and density. For density, no effect resulting
from the comonomer type was observed. This same inverse relationship was also
observed for tensile strength. Modulus, hardness and impact strength, on the other
hand, did show an effect resulting from the comonomer type. Modulus and hardness
were not depressed as much and impact strength improved more than what was
expected from calculations based on branch size. Homogeneous copolymers have
broad melting peaks. It was shown that at sufficiently high comonomer content, peak
broadening occurs when the higher cc-olefins are used as comonomer, which also
indicates that more random comonomer distributions are obtained with the higher aolefins.
From the chain propagation probabilities calculated it was observed that two
types of active sites are present. Those responsible for producing mainly
polyethylene have an alternating character while the sites capable of incorporating
comonomer have a blocky character.
It was expected that the additional introduction of a third a-olefin during ethylene / 1-
pentene copolymerization will produce a terpolymer with density and related
properties similar to the mathematical average between those of the relevant
copolymers. This was only observed for the terpolymers containing l-heptene, 1-
octene and l-nonene. The I-butene containing terpolymers have densities well below
the expected values while the I-hexene containing terpolymers have values very
similar to that of the ethylene / l-hexene copolymer densities, but still below the
expected values. Properties related to density, such as tensile strength and modulus,
follow this same trend. It is believed that the presence of l-pentene breaks up the tendency of the lower c-olefins to cluster which results in improved randomness.
Compared to the copolymers, I-butene and l-hexene containing terpolymers seem to
reach the impact strength maximum at a lower total comonomer content than that of
the I-pentene copolymers which also indicates an enhanced effect from the combined
use of I-pentene with these o-olefins. No substantial difference between impact
strengths of co- and terpolymers prepared with higher a-olefins was observed.
In general, the melting temperatures of the terpolymers are slightly lower and spread
over a wider temperature range than those of the copolymers which can be realized if
the comonomer units are less clustered and thus more randomly distributed. Decrease
in melting temperature was, however, not as much as for the metallocene catalyzed
terpolymers.
From sequence length calculations from l3C NMR spectroscopy it was found that the
crystallizable ethylene sequences of l-butene containing terpolymers were shorter
than those of the corresponding copolymers, which confirms the notion that the
introduction of a third comonomer resulted in an increase in randomness.
Crystallizable sequence lengths became gradually shorter when higher cc-olefins were
used in co- and terpolymers and those of the terpolymers are generally shorter.
From the different types of active centers present on a Ziegler-Natta catalyst, it was
reasoned that three main types of polymer chains can be present in the terpolymers:
(a) ethylene homopolymer, (b) ethylene / lower a-olefin copolymer and (c) ethylene /
lower a-olefin / higher a-olefin terpolymer. The ratio between these components in
the final terpolymer depends primarily on the size of the higher a-olefin. The larger
the third a-olefin becomes, the more active sites will reject it, resulting in a higher
amount of ethylene / lower a-olefin copolymer. It was thus suggested that the large
decrease in density and the associated change in related properties observed for
ethylene / l-pentene / l-butene terpolymers can be related to the combined result of
improved random comonomer incorporation together with the decrease in the amount
of ethylene homopolymer. The possibilities of using the higher a-olefins having uneven carbon numbers were
investigated in random propylene copolymers. Similar to that observed for the
ethylene copolymers, less of the higher a-olefins was necessary to achieve a certain
level of crystallinity. A good agreement was observed between tensile properties and
comonomer type and content and the size of the branch and the resulting defect it
causes in the crystal structure is the primary factor affecting tensile strength. For
impact strength a close correlation between the size of the comonomer side chain and
comonomer content was observed. It was shown that the effect of the heptyl branch
derived from a l-nonene unit was 2.3 times that of the propyl group derived from the
I-pentene unit.
Properties of block copolymers can not be related directly to l-pentene content as is
the case with random copolymers, mainly due to the heterogeneity of the block
copolymers. The activating effect of hydrogen on catalyst activity was observed. It
was also observed that the amount of l-pentene incorporated in the copolymer as well
as the copolymer yield were higher in the presence of hydrogen than when the
reaction was carried out in the absence of hydrogen.
By using DSC it was possible to identify different crystalline phases in the propylene
/ I-pentene block copolymers due to the differences in their crystallization kinetics. A
connection between the low-temperature peak and impact strength was observed. It
was found that the presence of the low-temperature peak resulting from thin lamellae
formed by chain containing many defects was undesirable when high impact strength
is required. It was not possible to quantify the extent to which the intensity of this
peak affected mechanical properties of the block copolymers. However, from
sequence length calculations it was found that the ratio between the propylene and 1-
pentene sequence lengths could be related quantitatively to impact strength, modulus,
hardness and tensile strength of the polymers investigated. / AFRIKAANSE OPSOMMING: 'n Verskeidenheid van verskillende «-olefiene word in die Sasol Fischer- Tropsch
proses vervaardig. Sasol het onlangs begin om hierdie a-olefiene aan
polimeervervaardigers te bied. Om die toepassingsmoontlikhede van hierdie aolefiene
as komonomere vir etileen en propileen polimerisasie te demonstreer was dit
nodig om eerstens 'n katalis met 'n kombinasie van hoë aktiwiteit en goeie
komonomeer invoeging te sintetiseer. In die geval van propileen word voldoende
stereospesifisiteit ook vereis.
Verskillende metodes om kataliste wat aan hierdie vereistes voldoen te vervaardig is
ondersoek. Daar is gevind dat kataliste waarvan die MgCb basis deur 'n kombinasie
van chemiese- en meganiese metodes geaktiveer is, die vereiste eienskappe besit. Die
hoeveelheid alkohol gebruik tydens die basis aktivering stap en die tyd toegelaat vir
die alkilering van die aktiewe spesies was belangrik. Geen duidelike verband tussen
totale titaan inhoud en aktiwiteit is waargeneem nie. Die mate waartoe aktiewe
spesies beskerm is, is bepaal vanaf die hoeveelheid komonomeer teenwoordig in die
finale kopolimeer in verhouding met die hoeveelheid bygevoeg tydens die reaksie.
Siklopentadieen is gebruik om onbeskermde aktiewe spesies selektief te deaktiveer
om die verhouding tussen beskermde en oop aktiewe spesies te bepaal. Hoëaktiwiteit
kataliste is nie geskik vir gasfase kopolimerisasie nie en is gevolglik verdun
deur dit te versprei in 'n voorafgevormde polimeer poeier en deur prepolimerisasie.
Katalis aktiwiteit gebaseer op titaan inhoud was aansienlik laer maar komonomeer
invoeging was nie merkbaar beinvloed nie.
Kataliste VIr die vervaardiging van kristallyne polipropileen vereis die
teenwoordigheid van beide interne- en eksterne elektron donors. Daar is gewys dat
isotaktisiteit liniêr verhoog met 'n toename in eksterne modifiseerder ten koste van katalis aktiwiteit en dat 'n dubbele behandeling van die basis of katalis, voor die finale
titaan fiksering, meer effektief was om stereospesifisiteit te verhoog. Die spesies met
laer stereospesifisiteit is meer bevoeg om bonkige komonomere in die koërdinasie
kompleks toe te laat en deur dus die konsentrasie van hierdie spesies te verlaag is die
bevoegdheid van die katalis om bonkige komonomeer te inkorporeer, verlaag.
Komonomeer reeksverspreiding en gemiddelde lamellêre dikte van verskillende
etileen / o-olefien kopolimere is bereken vanaf CH2 diad konsentrasie bepaal deur
KMR spektroskopie. Etileen reekse in die kopolimere wat l-buteen bevat is oor die
algemeen langer as dié waarin 'n hoër a-olefien as komonomeer gebruik was, wat
aandui dat 'n meer egalige komonomeer verspreiding verkry word as hoër «-olefiene
gebruik word. Daar is getoon dat 'n inverse verhouding tussen die grootte van die
vertakking en digtheid bestaan. Geen effek komende van die komonomeer tipe kon
waargeneem word nie. Hierdie soortgelyke inverse verhouding was ook waargeneem
vir treksterkte. Modulus, hardheid en impaksterkte aan die ander kant, hét 'n effek
komende van die komonomeer tipe getoon. Modulus en hardheid was nie soveel
verlaag, en impak sterkte soveel verhoog as wat verwag is vanaf berekeninge
gebaseer op vertakking grootte nie. Homogene kopolimere toon breë smeltpieke.
Daar is gewys dat by voldoende komonomeer inhoud 'n verbreding van die pieke
voorgekom het wanneer hoër a-olefiene as komonomere gebruik is, wat ook aandui
dat 'n meer egalige komonomeer verspreiding met hierdie c-olefiene verkry kan
word. Vanaf berekening van die ketting voortplantingsmoontlikhede is waargeneem
dat twee tipes aktiewe spesies teenwoordig is. Die verantwoordelik vir die vorming
van polietileen het 'n alternerende karakter terwyl die sentra wat komonomeer kan
inkorporeer 'n blokagtige karakter het.
Daar is verwag dat die addisionele byvoeging van 'n derde o.-olefien tydens etileen /
I-penteen kopolimerisasie, 'n terpolimeer met digtheid en verwante eienskappe
soortgelyk aan die wiskundige gemiddelde tussen dié van die relevante kopolimere tot
gevolg sal hê. Dit was egter slegs waargeneem vir terpolimere wat I-hepteen 1-
okteen en l-noneen bevat. Die I-buteen bevattende terpolimere het digthede ver
onder die verwagte waardes terwyl die I-hekseen bevattende terpolimere waardes
soortgelyk aan die etileen / l-hekseen kopolimeer digthede het' wat steeds onder die verwagte waardes is. Eienskappe verwant aan digtheid, soos treksterkte en modulus,
volg dieselfde neiging. Dit word geglo dat die teenwoordigheid van l-penteen die
neiging van die laer a-olefiene om saam te bondelopbreek wat 'n verbeterde
egaligheid in komonomeerverspreiding tot gevolg het. Vergeleke by die kopolimere
blyk dit dat die terpolimere wat l-buteen en I-hekseen bevat, die impaksterkte
maksimum by 'n laer totale komonomer inhoud bereik as dié van die 1-penteen
polimere. Dit dui ook op 'n verbeterde effek as gevolg van die gekombineerde
gebruik van l-penteen met ander a-olefiene. Geen duidelike verskil tussen die
impaksterktes van ko- en terpolimere, wat met die hoër a-olefiene berei was, is
waargeneem me.
In die algemeen is die smeltingstemperature van die terpolimere effens laer, en
versprei oor 'n wyer temperatuurgebied as dié van die kopolimere wat verklaar kan
word as komonomere minder saamgebondel is en dus meer homogeen versprei is.
Die afname in smelt temperatuur was egter nie soveel as dié van die metalloseengekataliseerde
terpolimere nie.
Vanaf reekslengte berekeninge met behulp van KMR spektroskopie is daar gevind dat
die kristalliseerbare etileen reekse van die l-buteen bevattende terpolimere korter was
as dié van die ooreenkomstige kopolimere, wat die gevoel dat die byvoeging van 'n
derde komonomeer 'n verbeterde komonomeerverspreiding tot gevolg het, bevestig.
Vanaf die verskillende aktiewe spesies teenwoordig in 'n Ziegler-Natta katalis is daar
geredeneer dat drie hooftipes polimeerkettings in die terpolimere teenwoordig kan
wees: (a) etileen hompolimeer, (b) etileen / laer a-olefien kopolimeer en (c) etileen /
laer a-olefien / hoër a-olefien terpolimeer. Die verhouding tussen hierdie
komponente in die finale terpolimeer hang primêr van die grootte van die hoër aolefien
af. Hoe groter die derde a-olefien is, deur hoe meer van die aktiewe spesies
sal dit verwerp word wat 'n groter hoeveelheid etileen / laer a-olefien kopolimeer tot
gevolg sal hê. Daar word dus voorgestel dat die groot afname in digtheid en die
geassosieerde veranderings in die toepaslike eiensappe waargeneem vir etileen / 1-
penteen / I-buteen terpolimeere, herlei kan word na die gekombineerde effek van verbeterde komonomeerverspreiding tesame met die afname lil die hoeveelheid
etileen homopolimeer.
Die moontlikheid om hoër cc-olefiene met onewe koolstofgetalle te gebruik in
homogene propileen kopolimere is ondersoek. Soortgelyk aan dit wat waargeneem is
vir die etileen kopolimere, was minder van die hoër cc-olefiene nodig om 'n spesifieke
vlak van kristalliniteit te bereik. 'n Goeie ooreenkoms tussen trek-eienskappe en .
komonomeer tipe- en inhoud is waargeneem en die grootte van die vertakking en die
gevolglike defek wat dit veroorsaak in die kristal struktuur is die primêre faktor wat
treksterkte beinvloed. Vir impaksterkte is 'n noue verband tusssen die grootte van die
vertakking en komonomeer inhoud waargeneem. Daar is aangetoon dat die effek van
die heptiel vertakking vanf die l-noneen eenheid 2.3 keer dié van die propiel groep
van die l-penteen eenheid is.
Eienskappe van blok kopolimere kan nie direk na l-penteen inhoud herlei word soos
die geval met die homogene kopolimere was nie, hoofsaaklik as gevolg van die
heterogeniteit van die blok kopolimere. Die aktiverende effek van waterstof op katalis
aktiwiteit is waargeneem. Daar is ook gesien dat die hoeveelheid l-penteen
geïnkorporeer in die kopolimeer, sowel as die kopolimeer opbrengs, hoër was in die
teenwoordigheid van waterstof as wanneer die reaksie sonder waterstof uitgevoer is.
Deur DSC te gebruik was dit moontlik om verskillende kristallyne fases in die
propileen / l-penteen blok kopolimere vanaf die verskille in hulle krisallisasie
kinetika, te identifiseer. 'n Verbintenis tussen die lae-temperatuur piek en
impaksterkte is waargeneem. Daar is gevind dat die teenwoordigheid van die laetemperatuur
piek, komende van die dun lamellas gevorm, deur kettings wat baie
defekte bevat, ongewens is wanneer hoë impaksterkte vereis word. Dit was nie
moontlik om die bereik waartoe die intensiteit van hierdie piek die meganiese
eienskappe van die blok kopolimere affekteer, te kwantifiseer nie. Vanaf reekslengte
bepalings is daar gevind dat die verhouding tussen die propileen en I-penteen
reekslengtes kwantitiatief herlei kan word na impaksterkte, modulus, hardheid en
treksterkte van die ondersoekte polimere.
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Adamantane copolymersCoetzee, Liezel 12 1900 (has links)
Thesis (PhD)--Stellenbosch University, 2001. / ENGLISH ABSTRACT: This study concerns the incorporation of adamantane containing monomers
3-(1-adamantyl)-1-propene and 1-(1-adamantyl)-4-vinylbenzene into ethene,
propene and higher a-olefins using different catalytic systems. The effect of the
incorporation of the adamantane monomer on the physical and thermal
properties of the polymers was investigated. A thorough study on the
background of adamantane in general, as well as polymerization reactions
involving the above-mentioned monomers and a-olefins was done.
3-(1-Adamantyl)-1-propene as well as 1,.(1-adamantyl)-4-vinylbenzene was
sucessfully synthesized. The homo polymers of each monomer were made. The
above-mentioned monomers were also polymerized:
• . 3-( 1-adamantyl)-1-propene with ethene, propene and higher a-olefins,
• 1-(1-adamantyl)-4-vinylbenzene with ethene and styrene.
The copolymers of 3-(1-adamantyl)-propene as well as 1-(1-adamantyl)-
4-vinylbenzene were characterized as far as possible to show the influence
of the incorporation of the adamantane group on the physical and chemical
properties of the polymers. A series of 3-phenyl-1-propene copolymers with
higher a-olefins were synthesized to compare the influence of the phenyl
group to the adamantyl group on the relevant properties of the polymers. / AFRIKAANSE OPSOMMING: Hierdie studie behels die inkorporasie van adamantaan-bevattende monomere,
3-( 1-adamantiel)-1-propeen en 1-(1-adamantiel)-4-vinielbenseen in eteen,
propeen en hoër a-olefiene met behulp van verskillende katalitiese sisteme. Die
effek wat die inkorporasie van die adamantaan monomeer op die fisiese en
chemiese eienskappe van die polimere het, is ondersoek. 'n Deeglike studie van
die agtergrond van adamantaan in die geheel, sowel as die polimerisasie
reaksies van die bogenoemde monomere met a-olefiene, is gedoen.
3-( 1-Adamantiel)-1-propeen sowel as 1-(1-adamantiel)-4-vinielbenseen is
suksesvol berei. Die homopolimere van bogenoemde monomere is
gesintetiseer. Bogenoemde monomere is gepolimeriseer:
• 3-(1-adamantiel)-1-propeen met eteen, propeen en hoër a-olefiene,
• 1-(1-adamantiel)-4-vinielbenseen met eteen en stireen.
Die kopolimere van 3-(1-adamantiel)-1-propeen en 1-(1-adamantiel)-
4-vinielbenseen is sover moontlik gekarakteriseer om die invloed van die
adamantaan groep op die fisiese en chemiese eienskappe van die polimeer
te toon. 'n Reeks kopolimere van 3-(1-feniel)-1-propeen met hoër a-olefiene
is gesintetiseer om die verwantskap tussen die invloed van die fenielgroep
en die adamantielgroep op die relevante eienskappe van die polimere te
toon.
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890 |
Innovative spectroscopic and chromatographic techniques for the analysis of complex polyolefins prepared by metallocene catalysisGraef, Sven Markus 12 1900 (has links)
Thesis (PhD)--Stellenbosch University, 2002. / ENGLISH ABSTRACT: The study focused on the analysis of a variety o f synthesised tailored copolymers.
During the investigation o f the samples new and innovative analytical techniques
were developed to be able to identify the presence of certain predicted or expected
copolymerisation products.
Emphasis was placed on the versatility of CRYSTAF as a method for the analysis of
semi-crystalline copolymers. Changes in the crystallisation temperature were used as
an indicator, while the type o f method, solvent and sample weight served as variables
in the system. The percentage comonomer content distribution for an unknown
sample was determined from the standard curve plotted with the aid o f copolymers
with known comonomer content.
Ethylene/higher a-olefin and propylene/higher a-olefm copolymers were synthesised
by means o f a metallocene precatalyst. In both cases, NMR spectroscopy, DSC, GPC,
and CRYSTAF were used as analytical tools. In the ethylene series it was shown that
the sample mixture was homogenous in the molar mass axis (GPC) but not in the
chemical composition axis (CRYSTAF) regarding the comonomer content. For the
propylene series, an increase in stereoerrors was observed by NMR and this was
correlated with crystallisation on heating a DSC for the range o f copolymers.
In the case where ethylene/methyl methacrylate block copolymers were synthesised
using metallocene precatalyst, novel detection and separation methods were used and
developed. This included the use o f CRYSTAF fitted with a carbonyl filter, high
temperature gradient HPLC and high temperature liquid chromatography under
critical conditions (LCCC). The last two techniques were the first where separation
could be achieved with samples only dissolving at high temperature. All previous
mentioned techniques, as well as the coupling of FTIR to GPC and high temperature
gradient HPLC via LC-Transform revealed that the samples consisted o f varying
ethylene and MMA block lengths. / AFRIKAANSE OPSOMMING: Die doelstelling van die navorsing was die analise van spesiaalvervaardigde
kopolimere. Nuwe analitiese tegnieke is vir die bevestiging van sekere voorgestelde
kopolimerisasie-produkte ontwikkel.
Klem is gelê op die veelsydigheid van CRYSTAF as ’n metode vir die analise van
gedeeltelik-kristallyne kopolimere. Veranderinge in die kristallisasie-temperature is
as respons gebruik, terwyl die metode van sintese, die oplosmiddel en die hoeveelheid
monster as veranderlikes in die sisteem beskou is. ‘n Standaardkurwe vir
komonomeerinhoud is opgestel met behulp van kopolimere met ‘n bekende
komonomeerinhoud. Hierdie kurwe is gebruik om die komonomeerinhoudsverspreiding
van onbekende monsters te bepaal.
Etileen/hoër a-olefien- en propileen/hoër a-olefien-kopolimere is met behulp van ‘n
metalloseen pre-katalis gesintetiseer. In beide gevalle is KMR spektroskopie, DSC,
GPC en CRYSTAF gebruik om die analises uit te uitvoer. Met verwysing na
komonomeerinhoud is daar in die geval van die etileenreeks bevind dat die
monstermengsel homogeen is met betrekking tot die molere massa, maar nie met
betrekking tot die chemiese samestelling nie. Vir die propileenreeks is ’n verhoging
in die stereofoute met behulp van KMR waargeneem. Dit is gekorrelleer met
kristallisasie weens verhitting tydens DSC-bepalings vir die reeks kopolimere.
In die geval van die sinteses van etileen/metielmetakrilaat-blokkopolimere met
metalloseen as pre-katalis, moes nuwe waamemings- en skeidingstegnieke ontwikkel
word. Dit het die gebruik van CRYSTAF met ’n karbonielfilter, hoetemperatuurgradient-
HPLC en hoë-temperatuurvloeistofchromatografie onder kritiese
toestande ingesluit. Laasgenoemde twee tegnieke het vir die eerste keer skeiding van
monsters wat net by hoe temperature oplos, moontlik gemaak. Bogenoemde tegnieke,
sowel as die koppeling van FTIR met GPC en hoë-temperatuur-gradient-HPLC via
LC-transformasie het getoon dat die monsters etileen- en MMA-blokke met
verskillende lengtes bevat het.
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