Directed synthesis of polymer mesostructures

[摘要] ENGLISH ABSTRACT:The objective of this research was to produce discrete, nano-shaped polymeric structures on thesame length scale as, or one to one copies of, templates, deformable templates or structure-directinghosts.Polymerisation of hydrophobic organic monomers in high concentration surfactant solutions, leadsto the formation of shaped particles (rod-like, plank-like and ribbon-like particles) in themicrometer size range. The origin of these regularly shaped particles was investigated. It isproposed that they were not polymeric in nature, but formed by the crystallisation of the surfactantin the presence of electrolytes and ethanol as solvent. The polymeric particles that were formedwere found to be of spherical shape, and no directing of the shape was detected.Mesostructured hosts were then investigated for their possible use as structure-directing agents. Aseries of polyelectrolyte-surfactant complexes of polydiallylammonium chloride with sodiumsulphate surfactants (ranging from C10 to C16) were synthesised and characterised in terms of theirthermal, mechanical and structural properties. The complex of polydiallylammonium chloride andsodium dodecyl sulphate was selected as an appropriate self-assembled model system forinvestigations into the structure-directing properties of these new materials.The polymerisation of hydrophobic organic monomers, such as styrene and the di-functionalmonomer m-diisopropenylbenzene (m-DIB), within the above mesoscopically structuredpolyelectrolyte-surfactant complex as host, lead to the formation of unconventionally shapedpolymeric particles. The influence of the presence of monomers and guest polymers on the phasemorphology of the host was investigated by small angle X-ray analyses (SAXS) and dynamicmechanical analyses (DMA). SAXS analyses showed that these new, stable hosts can hold up to 17% guest polymer before phase disruption is encountered. These findings were supported bychanges in the mechanical properties, as determined by DMA. The transmission electronmicroscopy (TEM) images of particles obtained after polymerisation showed very clearly that thepoly-(m-DIB) did not form a continuous copy of the 3D hexagonal structure of the host, but rathercolloidal copies of a part of the host structure that swelled the most. The shapes of the polymermesostructures were dictated by the morphology of the phase of the structure-directing host, to produce nanosized wires (dimensions 4 by 100 nm), cigar-shaped particles (dimensions 8 by 50 nm)and fibrillar bent shapes (larger than 200 nm), as revealed by TEM.According to literature these are the first shaped, polymer nano-particles produced in a soft, selfassembled,organic templating host.

[发布机构] Stellenbosch University