Thesis (MSc)--Stellenbosch University, 2011. / ENGLISH ABSTRACT: In reverse iodine transfer polymerisation (RITP), chain transfer agents (CTAs) are
generated in situ from the reaction between 2,2’-azobis(isobutyronitrile) (AIBN) and
molecular iodine. This stage of RITP is the inhibition period, which ends when all
iodine has been consumed. The evolution of CTAs was studied for the
polymerisation reactions of n-butyl acrylate and styrene respectively. RITP of n-butyl
acrylate was performed at 70 °C. In situ 1H nuclear magnetic resonance (NMR)
experiments were carried out to study the evolution of CTAs during the inhibition
period of n-butyl acrylate polymerisation and the structures A-I and A-Mn-I (where A
represents the moiety originating from AIBN, M represents the monomer unit and n is
the mean number degree of polymerisation) were observed. A polymer with the
general structure A-Mm-I is formed. The molecular weight of poly(n-butyl acrylate)
(PnBA) was evaluated with size exclusion chromatography (SEC) and NMR.
Structural analysis of PnBA was done using NMR spectroscopy and matrix-assisted
laser desorption/ionisation time-of-flight (MALDI-ToF) mass spectrometry. Similar
conditions to those used for n-butyl acrylate polymerisation were used for RITP of
styrene. The evolution of CTAs during the inhibition period of styrene polymerisation
was studied using in situ 1H NMR. The inhibition period of styrene polymerised by
RITP was much shorter than expected. This is due the consumption of iodine in the
reaction between styrene and iodine which reversibly forms 1,2-diiodo-ethyl benzene.
The CTAs A-I and A-Mn-I are formed, as well as 1-phenylethyl iodide (1-PEI). The
molecular weight of polystyrene (PS) was determined using SEC and NMR and the
functionality was evaluated using 1H NMR. The structure of PS was confirmed with
1H NMR and MALDI-ToF mass spectrometry. By increasing the temperature of the
reaction, the inhibition period can be shortened. Both polymerisation systems retain
control over molecular weight with an increase in temperature, however, n-butyl
acrylate is limited due to the possible formation of mid-chain radicals. The formation
of an A–Mm–A population (direct combination of the initiator and styrene) in RITP of
styrene results in more initiator being consumed than for n-butyl acrylate, despite
limited conversion of styrene to polymer. / AFRIKAANSE OPSOMMING: In omgekeerde-jodium-oordrag polimerisasie, is die kettingoordragagente
gegenereer in situ van die reaksie tussen 2,2’-azobis(isobutironitriel) (AIBN) en
molekulêre jodium. Hierdie fase van RITP is die inhibisie tydperk wat eindig wanneer
alle jodium verbruik is. Die evolusie van kettingoordragagente is vir die
polimerisasiereaksies van butielakrilaat en stireen onderskeidelik bestudeer.
Omgekeerde-jodium-oordrag polimerisasie van butielakrilaat was uitgevoer by 70 °C.
In situ 1H kernmagnetieseresonans (KMR) eksperimente is uitgevoer om die evolusie
van die kettingoordragagente te bestudeer tydens die inhibisie van butielakrilaat
polymerisasie en die strukture A-I en A-Mn-I (waar A die gedeelte voorstel wat
afkomstig is van AIBN, M die monomeer-eenheid en n die gemiddelde aantal
polymerisasiegraad verteenwoordig) is ge-identifiseer. 'n Polimeer met die algemene
struktuur A-Mm-I is gevorm. Die molekulêre gewig van poli(butielakrilaat) (PnBA) was
geëvalueer deur grootte-uitsluitings chromatografie en KMR spektroskopie.
Strukturele ontleding van PnBA is gedoen deur die KMR spektroskopie en matriks
ge-assisteerde laser desorpsie/ionisasie tyd-van-vlug massaspektroskopie.
Soortgelyke kondisies as dié wat gebruik word vir butielakrilaat polymerisasie, is
gebruik vir omgekeerde-jodium-oordrag polimerisasie van stireen. Die evolusie van
die ketting oordrag agente gedurende die inhibisie periode van stireen polymerisasie
is deur in situ 1H KMR bestudeer en die inhibisie periode is baie korter as verwag. Dit
is as gevolg van die opname van jodium in die reaksie tussen stireen en jodium wat
omkeerbare stireen-di-jodied tot gevolg hê. Die ketting oordrag agente A-I en A-Mn-I
is gevorm, sowel as 1-feniel-etiel jodied. Die molekulêre massa van polistireen (PS)
is bepaal met behulp van grootte-uitsluitings chromatografie en KMR spektroskopie
en die funksioneering is geëvalueer met behulp van 1H KMR. Die struktuur van PS is
bevestig deur 1H KMR en matriks ge-assisteerde laser desorpsie/ionisasie tyd-vanvlug
massaspektroskopie. Deur die verhoging van die temperatuur van die reaksie,
kan die inhibisie periode verkort word. Beide polimerisasie sisteme behou beheer oor
die molekulêre massa met 'n toename in temperatuur, alhoewel butielakrilaat beperk
word as gevolg van die moontlike vorming van middel kettingradikale. Die vorming
van die A-Mm-A spesie (direkte kombinering van AIBN en stireen) in omgekeerdejodium-
oordrag polimerisasie van stireen veroorsaak dat meer AIBN verbruik word as
butielakrilaat, ten spyte van die beperkte omskakeling van stireen tot polimeer.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/17967 |
| Date | 12 1900 |
| Creators | Wright, Trevor |
| 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 |
| Rights | Stellenbosch University |
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