Thesis (MSc)--Stellenbosch University, 2000. / ENGLISH ABSTRACT: This work involves the study of the effects of Reversible Addition-Fragmentation Chain
Transfer (RAFT) agents on the emulsion polymerization of styrene. The feasibility of
RAFT as a method for obtaining controlled radical polymerizations in emulsion systems is
also investigated. Both seeded and ab initio systems were studied with three RAFT
agents of varying structure.
Inhibition and retardation effects on addition of various amounts of the RAFT agents to
the emulsion systems were observed and the trends noticed. The effect of the RAFT
agents on the average number of radicals per latex particle was calculated from reaction
rates. The effect of the RAFT agent on the molecular weight and the molecular weight
distribution was monitored by gel permeation chromatography.
Exit of free radicals from the latex particles proves to be a major feature in the studied
RAFT emulsion systems. Fragmentation of the RAFT agent in the latex particles, gives
rise to free radical species that can exit from the particle and enter other particles where
they can either terminate instantaneously or propagate. The exit and termination
processes presumably result in both the inhibition and retardation of the emulsion
polymerizations. A linear increase in Mn with conversion is observed, however the low
concentration of RAFT agent in the latex particles is responsible for the obtained number
average molecular weights being much higher than predicted. The low concentrations of
RAFT agents in the latex particles is also responsible for the broad molecular weight
distributions that are obtained.
Reaction conditions for RAFT experiments should to be chosen so that the effects of exit
processes are minimized and that the RAFT agent is primarily situated in the latex
particles. These conditions must be met if the RAFT process is to be successful as a
method of controlled radical polymerization in emulsions. / AFRIKAANSE OPSOMMING: Hierdie navorsing behels die studie van die effek van In bygevoegde addisie-fragmentasie
kettingsoordragsreagent (RAFT1) op die emulsie polimerisasie van stireen. Die
uitvoerbaarheid van RAFT as 'n metode om gekontroleerde radikale polimerisasies in
emulsiesisteme te verkry is ook ondersoek. Eksperimente met drie RAFTkettingoordragsreagente
van gevarieerde strukture is uitgevoer in beide seeded en ab
initia sisteme.
Die effek van die RAFT-reagent op die inhibisie en vertraging van die emulsie
polimerisasie is waargeneem en die invloed van RAFT op die gemiddelde aantal radikale
per partikel is bepaal. Die ontwikkeling van die molekulêre massa en die molekulêre
massadistribusie is waargeneem deur middel van gel permeasie- kromatografiese
tegnieke.
Die ontsnapping van vrye radikale vanuit die partikels was 'n belangrike faktor in RAFT emulsiesisteme
wat ondersoek is. Hierdie radikale is gegenereer deur die fragmentasie
van die oorspronklike RAFT-reagent. Fragmentasie van die RAFT-reagent in die lateks
partikels lei tot die vorming van vrye radikale spesies wat uit een partikel kan ontsnap en
ander partikels kan binnedring waar dit onmiddellik kan termineer of propageer. Die
ontsnappings- en terminasieprosesse van vrye radikale lei oënskynlik tot die inhibering en
vertraging van die emulsie polimerisasie.
'n Lineêre verhoging in die gemiddelde molekulêre massa tydens konversie is
waargeneem, alhoewel die Mn-waardes baie hoër was as wat verwag is. Die verskil kan
toegeskryf word aan die klein hoeveelhede van die RAFT-reagent wat in die partikels
teenwoordig is. Hierdie lae RAFT-konsentrasies is ook verantwoordelik vir die breë
molekulêre massa distribusie wat waargeneem is.
Vir die RAFT-proses om suksesvol te wees in gekontroleerde radikale polimerisasies in
emulsies, moet reaksie kondisies so gekies word dat die ontsnapping van vrye radikale
tot 'n minimum beperk word en die RAFT-reagent hoofsaaklik in die lateks partikels
teenwoordig is.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/51739 |
| Date | 03 1900 |
| Creators | Hodgson, Marcelle |
| Contributors | Sanderson, R. D., Monteiro, M. J., Stellenbosch University. Faculty of Science. Dept. of Chemistry & Polymer Science. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | Unknown |
| Type | Thesis |
| Format | 114 p. : ill. |
| Rights | Stellenbosch University |
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