Synthesis and characterisation of hybrid graft copolymers of polydimethylsiloxane and polymethylmethacrylate
Date
2007-12
Authors
Krugel, Gretha
Journal Title
Journal ISSN
Volume Title
Publisher
Stellenbosch : University of Stellenbosch
Abstract
Hybrid graft copolymers of polydimethylsiloxane (PDMS) and polymethylmethacrylate
(PMMA) were synthesised. PDMS macromonomers were synthesised anionically from
the cyclic D3 monomer. This living polymerisation was terminated with a [3-
(methacryloxy)propyl]-dimethylchlorosilane terminating agent which resulted in the
functionalised macromonomer. These PDMS macromonomers and MMA monomer were
copolymerised to form PMMA-g-PDMS hybrid copolymers by conventional free radical
reactions. Synthesised and commercial methacryloxy-functionalised PDMS
macromonomers having a range of molar masses were copolymerised with MMA to form
graft copolymers of various chemical compositions. PDMS content in the graft
copolymers could be varied by the amount of PDMS incorporated into the copolymer as
well as by varying the length of the PDMS side chains. Size exclusion chromatography
(SEC) results confirmed low PDI’s for the PDMS macromonomers synthesised
anionically. NMR studies allowed characterisation of the synthesised PDMS
macromonomers and PMMA-g-PDMS copolymers. It also allowed the determination of
relative ratios of PMMA:PDMS in the graft copolymers. Gradient elution chromatography
(GEC) was used successfully to monitor the presence and removal of the PDMS
macromonomer from the graft copolymer products. The influence of PDMS content of
the graft copolymers on retention time was also evaluated using this technique. Two
dimensional chromatography confirmed the formation of PMMA-g-PDMS copolymer as
well as PMMA homopolymer during some of the grafting reactions. GEC in the first
dimension was coupled to SEC in the second dimension. PAS-FTIR studies allowed
chemical characterisation of the graft copolymer and confirmed surface segregation of
the PDMS. Atomic force microscopy (AFM) was also used to study the surface
segregation of PDMS and looked at the relationship between surface polarity and
increasing PDMS content. The study showed the effect of thermal treatment on the
surface morphology of the hybrid polymers. Corona treatment was used to modify the
surface structure of the graft copolymer films. Contact angle studies provided evidence
of hydrophobic loss and recovery after corona for the hybrid polymer materials
containing PDMS. This is one of the first reported examples of hydrophobicity recovery
in these types of hybrid materials after corona treatment. Slow positron beam studies
highlighted the formation of a thin silica like layer on the surface of the films after corona
similar to that observed for pure cross-linked PDMS compounds. The positron studies
enabled estimation of the thickness of the silica like layer.
Description
Thesis (MSc (Chemistry and Polymer Science))--University of Stellenbosch, 2007.
Keywords
Synthesis of graft copolymers, Polymers analysis, Dissertations -- Chemistry, Theses -- Chemistry