Thesis (PhD)--Stellenbosch University, 2015. / ENGLISH ABSTRACT: Synthetic polymers are complex compounds that have multiple distributions with
regard to molar mass, chemical composition, functionality and molecular architecture.
Therefore, the molecular complexity of these compounds can only be analysed using
a combination of analytical techniques.
Well-defined complex polymers can be prepared by different types of living radical
polymerisation, including reversible addition–fragmentation chain transfer
polymerisation (RAFT) and reverse iodine transfer polymerisation (RITP). Using
these techniques, several different homopolymers and copolymers have been
prepared. However, there is still space for some more extended research.
Many different types of multifunctional RAFT agents have been reported in literature.
A tetrafunctional RAFT agent was prepared in our laboratory and used for the first
time in the polymerisation of styrene. The polymerisation reaction was followed using
in situ 1H nuclear magnetic resonance (NMR) and the molar masses of the resultant
polymers were determined using size exclusion chromatography (SEC). The molar
masses of the star-shaped polystyrenes (PS) were found to be less than the
theoretical molar masses. This was due to the fact that SEC was calibrated with
linear PS standards, while the samples under investigation are branched. Linear and
branched polymers have different hydrodynamic volumes at similar molar masses. In
order to prove that the star-shaped polymers were in fact four-armed, the samples
were cleaved by aminolysis to yield the linear PS arms. The molar masses of the
arms were in agreement with the theoretical arm molar masses based in the fourarmed
structure.
RITP is a relatively new living radical polymerisation technique. Various monomers
have been prepared using RITP, including acrylates, methacrylates and styrene. The
polymers formed using this technique have been characterised by techniques such
as SEC, NMR and mass spectrometry (MS). However, very little advanced
characterisation work has been done on polymers synthesised via RITP.
Polystyrene-block-poly(n-butyl acrylate) (PS-b-PBA) block copolymers were prepared
via RITP and the microstructure analysed by in situ NMR and other advanced
analytical techniques. The chromatograms from gradient HPLC of the PS-b-PBA
block copolymers showed a separation based on chemical composition. The
preparation of deuterated polymers via RITP has not been reported in literature.
Hydrogenous-polystyrene-block-deuterated-polystyrene (hPS-b-dPS) was
synthesised via RITP and analysed using liquid chromatography at critical conditions.
An isotopic separation was achieved when critical conditions were established for
hydrogenous PS (h-PS). A separation of the block copolymer from the first block was
also achieved under chromatographic conditions where the block copolymer eluted in
SEC mode while the first block eluted in LAC mode. The separation according to the
block structure was confirmed by two-dimensional liquid chromatography. / AFRIKAANSE OPSOMMING: Sintetiese polimere is komplekse verbindings wat meervoudige verspreidings ten
opsigte van molêre massa, chemiese samestelling, funksionaliteit en molekulêre
argitektuur. Daarom kan die molekulêre kompleksiteit van hierdie verbindings net
ontleed word met behulp van 'n kombinasie van analitiese tegnieke.
Goed-gedefinieerde komplekse polimere kan voorberei word deur verskillende soorte
lewende radikaal polimerisasie, insluitend omkeerbare addisie-fragmentasie
kettingoordrag polimerisasie (OAFO) en omgekeerde jodium oordrag polimerisasie
(OJOP). Met behulp van hierdie tegnieke, was verskeie homopolimere en kopolimeer
opgestel. Maar daar is nog plek vir nog uitgebreide navorsing.
Baie verskillende tipes multifunksionele OAFO agente is aangemeld in die
letterkunde. Ons het 'n nuwe vier-armige OAFO agent in ons laboratorium voorberei
en dit was vir die eerste keer in die polimerisasie van stireen gebruik. Die
polimerisasie reaksie is gevolg met behulp van in situ 1H kernmagnetieseresonans
(KMR) en die molêre massas van die gevolglike polimere was bepaal deur grootteuitsluitings
chromatografie (SEC). Die molêre massas van die ster-polistireen (PS) is
bevind as minder as teoretiese molêre massas. Dit is omdat SEC instrumente
gekalibreer word met lineêre PS standaarde, terwyl die monsters wat tans ondersoek
word vertakte polimere is. Lineêre en vertakte polimere het verskillende
hidrodinamiese volumes by soortgelyke molêre massas. Ten einde te bewys dat die
ster polimere in werklikheid vier-armig is, is die monsters gesny deur ‘n aminolisasiereaksie
om die lineêre PS arms te lewer. Die molêre massas van die arms was
ooreenkomstig met die teoretiese arm molêre massas gebaseer op die vier-armige
struktuur.
OJOP is 'n relatiewe nuuts lewende radikaal polimerisasie tegniek. Verskeie
monomere is opgestel deur OJOP, insluitend akrilate, metakrilate en stireen. Die
polimere wat gevorm is deur middel van die tegniek is al gekenmerk deur tegnieke
soos SEC, KMR en massaspektrometrie (MS). Tog is daar baie min gevorderde
karakterisering werk gedoen oor polimere gesintetiseer deur middel van OJOP.
Polistireen-blok-poli(n-butylacrylaat) (PS-b-PBA) blokkopolimere was voorberei deur
middel van OJOP en die mikrostruktuur ontleed met behulp van gevorderde
analitiese tegnieke. Die chromatogramme van gradiënt HPLC van die PS-b-PBA
blokkopolimere het 'n skeiding ondergaan gebaseer op die chemiese samestelling.
Die voorbereiding van gedeutereerde polimere deur middel van OJOP word nie in die
letterkunde gevind nie. Gehidrogeneerde-polistireen-blok-gedeutereerde-polistireen
(hPS-b-dPS) is gesintetiseer deur middel van OJOP en ontleed met behulp van
vloeistofchromatografie onder kritiese kondisies. 'n Isotopiese skeiding was bereik
wanneer kritiese kondisies gestig is vir gehidrogeneerde PS (h-PS).'n Skeiding van
die blok kopolimeer van die eerste blok was ook bereik onder chromatografiese
omstandighede waar die blok kopolimeer elueer in SEC terwyl die eerste blok elueer
in LAC. Die skeiding volgens die blok struktuur was bevestig deur twee-dimensionele
vloeistofchromatografie.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/96744 |
| Date | 04 1900 |
| Creators | Wright, Trevor Gavin |
| 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 | xxi, 102 pages : colour illustrations |
| Rights | Stellenbosch University |
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