Thesis (PhD)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: Complex polymer systems have multiple distributions with regard to molecular parameters
such as molar mass, functionality, chemical composition, molecular architecture and
microstructure. These distributions affect the properties of the polymers making it necessary
to develop separation methods to be able to correlate structure to property. A single onedimensional
chromatographic method is usually not sufficient to separate these complex
polymers with respect to all the distributions. Hence, multidimensional liquid chromatography
is necessary for the complete analysis of complex polymers using two or more
chromatographic techniques before detection.
In this work, two novel liquid chromatographic methods were developed to separate complex
polymers according to microstructure. Comprehensive two-dimensional liquid
chromatography (LC x LC) was carried out to observe the correlation between microstructure
and molar mass. The separation according to microstructure was coupled to NMR (LC-NMR)
to observe, identify and quantify the different microstructural components during
chromatographic elution. The first chromatographic method separated hydrogenated and deuterated polystyrene
homopolymers with respect to the isotope effect. For the LC x LC experiments, liquid
chromatography at critical conditions (LCCC) was employed as the first dimension separating
according to the isotope effect and size exclusion chromatography (SEC) as the second
dimension separating according to molar mass. The LC x LC results of the blends showed that
there was an improvement in isotopic separation with an increase in molar mass. The LCNMR
coupling using both 1H and 2H NMR detection allowed for the identification of low
molar mass blend components which were not sufficiently separated by liquid
chromatography.
The second chromatographic method separated stereoregular poly(methyl methacrylate)s
(PMMAs) with respect to tacticity. The LC x LC experiments of stereoregular PMMAs
utilised solvent gradient liquid chromatography as the first dimension to separate according to
tacticity and size exclusion chromatography (SEC) as the second dimension to separate
according to molar mass. The LC x LC results showed a change in the triad composition with elution of the stereoregular PMMAs with a slight influence of molar mass. The LC-NMR
coupling allowed the observation of the triad composition during chromatographic elution. / AFRIKAANSE OPSOMMING: Komplekse polimeriese sisteme het meervoudige verspreidings ten opsigte van molekulêre
parameters, soos byvoorbeeld, molêre massa, funksionaliteit, chemiese samestelling,
molekulêre argitektuur en mikrostruktuur. Hierdie verspreidings beïnvloed die eienskappe van
die polimere en dus is dit nodig om skeidingsmetodes te ontwikkel ten einde
polimeerstruktuur met polimeereienskappe te kan korreleer. ‘n Enkele een-dimensionele
chromatografiese metode is gewoonlik nie voldoende om hierdie komplekse polimere te skei
met betrekking tot al die verspreidings nie. Multidimensionele vloeistofchromatografie, met
die insluiting van twee of meer chromatografiese tegnieke, is dus nodig om polimere te skei
voor waarneming kan plaasvind.
Twee nuwe chromatografiese metodes is ontwikkel om komplekse polimere volgens
mikrostruktuur te skei. Twee-dimensionele vloeistofchromatografie (LC x LC) is uitgevoer
ten einde die korrelasie tussen mikrostruktuur en molêre massa te ondersoek. Daarna is die
skeiding wat op mikrostruktuur gebasseer is, gekoppel aan KMR (LC-KMR) om die
verskillende mikrostrukturele komponente gedurende chromatografiese eluering waar te
neem, te identifiseer en te kwantifiseer.
Die eerste chromatografiese metode het die gehidrogeneerde en gedeutereerde polistireen
geskei met betrekking tot die isotoopeffek. Hier het die LC x LC skeiding bestaan uit
vloeistofchromatografie onder kritiese kondisies (LCCC) as die eerste dimensie, wat skeiding
bewerkstellig het gebasseer op die isotoopeffek, en grootte-uitsluitingschromatografie (SEC)
as die tweede dimensie, wat skeiding bewerkstellig het gebasseer op die molêre massa. Die
LC x LC resultate van die vermengings het ‘n verbetering in isotopiese skeiding met ‘n
toename in molêre massa getoon. Deur gebruik te maak van die LC-KMR koppeling, waar
beide 1H en 2H KMR waarneming gebruik is, was dit moontlik om die lae-molêre-massakomponente
van vermengings wat nie volledig d.m.v. LC geskei kon word nie, te identifiseer. Die tweede chromatografiese metode het stereoreëlmatige polimetielmetakrilate (PMMAs)
m.b.t. taktisiteit geskei. Die LC x LC skeiding van stereoreëlmatige PMMAs het bestaan uit
oplosmiddel -gradiënt-LC as eerste dimensie om volgens taktisiteit te skei, en SEC as tweede
dimensie om volgens molêre massa te skei. Die LC x LC resultate het ‘n molêre massa
afhanklikheid van stereoreëlmatige PMMAs op taktisiteit getoon. Die LC-KMR koppeling het
dit moontlik gemaak om die triade-samestelling gedurende chromatografiese eluering waar te
neem.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/86227 |
| Date | 04 1900 |
| Creators | Maiko, Khumo Gwendoline |
| Contributors | Pasch, Harald, Stellenbosch University. Faculty of Science. Dept. of Chemistry and Polymer Science. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
| Format | xxv, 91 p. : ill. (some col.) |
| Rights | Stellenbosch University |
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