Browsing by Author "Weideman, Inge"
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- ItemOrganocatalytic anionic polymerization of o-phthaldialdehyde and n-butyraldehyde(Stellenbosch : Stellenbosch University, 2017-03) Weideman, Inge; Pfukwa, Rueben; Klumperman, Bert; Stellenbosch University. Faculty of Science. Dept. of Chemistry and Polymer Science.ENGLISH ABSTRACT: Self-immolative polymers (SIPs) can be defined as polymers that are capable of complete head-to-tail depolymerization upon cleavage of an end-cap from the polymer chain-end in response to a trigger/stimulus. The use of SIPs has emerged as an alternative strategy in designing smart materials that are capable of responding to selective signals and provide an amplified response since the depolymerization process converts the entire polymer into its monomeric units and other small molecule products that can play a role in the amplified response. The incorporation of these polymers also offers the opportunity to alter the properties of a material after it has been prepared since the depolymerization of the SIP can cause a change in the shape, internal structure and/or surface properties of the material. Poly(phthaldialdehyde) (PPA), a well-known SIP, has been successfully prepared via non-organometallic catalyst based anionic polymerization in recent years. However, the methods that have been reported require expensive reagents and delicate experimental conditions. Hence, a new facile method for the non-organometallic anionic polymerization of PA was introduced and optimized in this work. The effect of a range of phosphazene and amine base catalysts were investigated. The results showed 1,8-diazabicyclo[5.4.0]undec-7-ene with a catalyst to initiator ratio of four to be the ideal catalytic system. It was further determined that the optimum experimental conditions for the DBU catalyzed system consisted of a 1.0 M monomer concentration, tetrahydrofuran as solvent and a reaction time of ten minutes. It was also shown that carboxylic acids can be used to initiate the polymerization reaction, which has thus far only been achieved using primary alcohols. The optimized method for the preparation of PPA was applied to the preparation of polystyrene-poly(phthaldialdehyde) block copolymers (BCPs). Hydroxyl end-functional polystyrene was prepared via activator regenerated by electron transfer atom transfer radical polymerization to serve as macroinitiator for the BCP reaction. Analysis of these BCPs, revealed that they had been prepared with narrow molecular weight distributions and a good agreement between the theoretical and experimentally obtained molecular weights. A systematic study was carried out to optimize the preparation of poly(butyraldehyde) (PBA), a SIP that has to date only been prepared using organometallic catalysts, by non-organometallic catalyst based anionic polymerization. The results of the study showed the phosphazene base catalyst P2-t-Bu with a catalyst to initiator ratio of 1 to 1 to be the ideal catalytic system for the preparation of PBA. Further investigation revealed a monomer concentration of 1.0 M, a nonpolar solvent such as pentane and a reaction time of ten minutes to be the optimum experimental conditions for the phosphazene base catalytic system.