Dissertation (MSc)--University of Stellenbosch, 2007. / ENGLISH ABSTRACT: Polymers prepared via radical techniques are very common in our every day environment. The
technique is however limited by a lack of control over the polymerization and an inability to
produce block copolymers. Block copolymers have a significant number of potential applications in
advanced materials and as a result are a field in which significant research is being conducted.
Reversible Addition-Fragmentation chain transfer (RAFT) is a living free radical process that
overcomes the disadvantages inherent in the traditional process.
In this study the mediation behaviour of two inherently different RAFT agents was investigated by
the “living” free radical polymerization of model monomers via the RAFT process in homogeneous
and aqueous dispersed media with the focus on differentiating between the two types of agents. To
ensure that the agents were comparable a new RAFT agent had to be prepared which has not
previously been documented. The efficiency of the RAFT agents was compared in terms of rate
effects, the predictability of the molecular weights of the polymers, the polydispersities of the
polymers and their ability to allow block copolymer formation via sequential addition of monomers.
Block copolymerizations were conducted by the addition of new monomer to the already existing
RAFT end-capped chains. Monomer addition was done via three different approaches; namely shot
addition, feed addition and pre-swelling (in the case of emulsions). Chromatographic analysis was
conducted on the resulting block copolymers via liquid chromatography at critical conditions (LCCC),
and its online coupling with size-exclusion chromatography (SEC) to obtain two-dimensional
information on the differences in heterogeneity of their molecular distributions. Other analyses
included dynamic light scattering analysis (DLS) and transmission electron microscopy (TEM).
The detailed analysis enabled the understanding of the different products that are produced via the
two different classes of RAFT agent. Potential causes for the differences are discussed and possible
areas for future research are highlighted. The work presented here is the most detailed investigation
of this class of polymerization to date and will provide new insight for researchers working in this
vibrant and important research field. / AFRIKAANSE OPSOMMING: Polimere gesintetiseer deur die gebruik van radikaal tegnieke is algemeen in ons daaglikse
omgewing.
Die tegniek is egter beperk deur die gebrek aan beheer oor die polimerisasie en die onvermoë om
blokkopolimere te sintetiseer. Blokkopolimere beskik oor ‘n aansienlike hoeveelheid potensiele
aanwendinge in gevorderde materiale en is gevolglik ‘n belangrike navorsingsgebied. Omkeerbare
addisie fragmentasie ketting oordrag (OAFO) is ‘n lewende vrye radikaal proses wat die inherente
nadele van die tradisionele proses oorkom.
In die betrokke studie is die mediasie gedrag van twee verskillende OAFO agente bestudeer deur
die lewende vrye radikaal polimerisasie van model monomere deur die OAFO proses in homogene
en waterig dispersie media met die fokus op differensiering tussen die twee tipes agente. Om te
verseker dat die twee agente vergelykbaar is, is ‘n nuwe OAFO agent voorberei wat tot op hede nog
nie gedokumenteer is nie. Die effektiwiteit van die OAFO agente is vergelyk in terme van tempo
effekte, die voorspelbaarheid van die molekulêre massa van die polimere, die polidispersiteit van
die polimere en die moontlikheid om blokkopolimerisasie deur kronologiese byvoeging van
monomere te fasiliteer. Blokkopolimerisasie is uitgevoer deur die byvoeging van nuwe monomeer
tot die alreeds bestaande OAFO eind-groep kettings. Monomeer byvoegings is uitgevoer deur drie
verskillende metodes; naamlik vulskoot addisie, voer addisie en vooraf swelling (in die geval van
emulsies). Chromatografiese analise is uitgevoer op die resulterende blokkopolimere deur vloeistof
chromatografie by kritieke kondisie (LC-CC) en die aanlyn koppeling met grootte-uitsluiting
vloeistof chromatografie, om twee-dimensionele informasie omtrent die verskille in heterogeniteit
van hul molekulere verdeling te bepaal. Verdere analise sluit dinamiese verstrooing mikroskopie en
transmissie elektron mikroskopie in.
Die detaileerde analise onthul die samestelling van die verskillende produkte wat geproduseer is
deur die verskillende klasse van OAFO agent. Potensiele oorsake vir die verskille is bespreek en
moontlike areas vir toekomstige navorsing is benadruk. Die werk hier voorgestel is die mees
gedetaileerde navorsing van hierdie tipe klas van polymerisasie tot op hede en beloof nuwe insig vir
navorsers betrokke in hierdie dinamiese en belangrike navorsingsveld.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/21699 |
| Date | 12 1900 |
| Creators | Pretorius, Nadine O. |
| Contributors | Sanderson, R.D., McLeary, J.B., 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 | Unknown |
| Type | Thesis |
| Format | xxiii, 150 leaves : ill. |
| Rights | Stellenbosch University |
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