Thesis (MSc (Chemistry and Polymer Science))--University of Stellenbosch, 2007. / Hybrid A-B type block copolymers of polydimethylsiloxane (PDMS) and polystyrene (PS)
were synthesised. Three different synthetic routes, which allowed control over polymer
structure, were chosen to synthesise these block copolymers. The first technique, coupling of
functional prepolymers, involved using anionic polymerisation to produce PDMS and PS
functional prepolymers of controlled structure. These prepolymers were functionalised with
either silane or allyl functionality and then coupled using a hydrosilylation reaction with
Karstetds platinum catalyst. This technique was the least efficient in block synthesis due to
the incompatibility of the disparate prepolymers. The second technique under study,
sequential anionic polymerisation, gave excellent block copolymer formation with good
control over the chain architecture. The final technique employed atom transfer radical
polymerisation (ATRP) of styrene using a bromoisobutyrate functionalised PDMS
macroinitiator. Silane functional PDMS molecules underwent a hydrosilylation reaction with
allyl-2-bromo-2-methyl-propionate to produce the bromoisobutyrate functionalised polymer in
excellent yields. Subsequent ATRP with styrene allowed the successful synthesis of block
copolymers of controlled structure. Chromatographic systems that allowed liquid
chromatography at the critical conditions (LC-CC) of PS and gradient elution chromatography
(GEC) of the products were developed. GEC was used successfully in the monitoring of the
presence and removal of PDMS homopolymer present in the block copolymer products. LCCC
at the critical point of PS allowed successful chromatographic separation of PS
homopolymer from the block material, as well as, the molecular weight distribution of the
block material according to the segmental length of the PDMS component. LC-CC coupled to
FT-IR using a LC-transform device allowed successful characterisation of the block
copolymer chemical composition. Corona treatment was used to modify the surface structure
of the block copolymer films. Optical microscopy and slow positron beam studies highlighted
the formation of a thin silica like layer on the surface of the films after corona. The positron
studies enabled determination of the silica like layer’s thickness. Contact angle studies
provided the first evidence of hydrophobic loss and recovery for these PDMS containing
hybrid polymer materials after corona treatment. A novel offline coupling technique was
developed between LC-CC separation and transmission electron microscopy (TEM) analysis.
This allowed easy sample preparation without the difficult bulk extraction procedures needed
to remove homo-PS contaminants from the block copolymer. This technique also provided
morphological information as a function of PDMS segmental length.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/2890 |
| Date | 03 1900 |
| Creators | Bayley, Gareth Michael |
| Contributors | Mallon, P. E., University of Stellenbosch. Faculty of Science. Dept. of Chemistry and Polymer Science. |
| Publisher | Stellenbosch : University of Stellenbosch |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | 3196647 bytes, application/pdf |
| Rights | University of Stellenbosch |
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