Synthesis and characterisation of hybrid graft copolymers of polydimethylsiloxane and polymethylmethacrylate

[摘要] Hybrid graft copolymers of polydimethylsiloxane (PDMS) and polymethylmethacrylate(PMMA) were synthesised. PDMS macromonomers were synthesised anionically fromthe cyclic D3 monomer. This living polymerisation was terminated with a [3-(methacryloxy)propyl]-dimethylchlorosilane terminating agent which resulted in thefunctionalised macromonomer. These PDMS macromonomers and MMA monomer werecopolymerised to form PMMA-g-PDMS hybrid copolymers by conventional free radicalreactions. Synthesised and commercial methacryloxy-functionalised PDMSmacromonomers having a range of molar masses were copolymerised with MMA to formgraft copolymers of various chemical compositions. PDMS content in the graftcopolymers could be varied by the amount of PDMS incorporated into the copolymer aswell as by varying the length of the PDMS side chains. Size exclusion chromatography(SEC) results confirmed low PDI's for the PDMS macromonomers synthesisedanionically. NMR studies allowed characterisation of the synthesised PDMSmacromonomers and PMMA-g-PDMS copolymers. It also allowed the determination ofrelative ratios of PMMA:PDMS in the graft copolymers. Gradient elution chromatography(GEC) was used successfully to monitor the presence and removal of the PDMSmacromonomer from the graft copolymer products. The influence of PDMS content ofthe graft copolymers on retention time was also evaluated using this technique. Twodimensional chromatography confirmed the formation of PMMA-g-PDMS copolymer aswell as PMMA homopolymer during some of the grafting reactions. GEC in the firstdimension was coupled to SEC in the second dimension. PAS-FTIR studies allowedchemical characterisation of the graft copolymer and confirmed surface segregation ofthe PDMS. Atomic force microscopy (AFM) was also used to study the surfacesegregation of PDMS and looked at the relationship between surface polarity andincreasing PDMS content. The study showed the effect of thermal treatment on thesurface morphology of the hybrid polymers. Corona treatment was used to modify thesurface structure of the graft copolymer films. Contact angle studies provided evidenceof hydrophobic loss and recovery after corona for the hybrid polymer materialscontaining PDMS. This is one of the first reported examples of hydrophobicity recoveryin these types of hybrid materials after corona treatment. Slow positron beam studieshighlighted the formation of a thin silica like layer on the surface of the films after coronasimilar to that observed for pure cross-linked PDMS compounds. The positron studiesenabled estimation of the thickness of the silica like layer.

[发布机构] Stellenbosch University