Browsing by Author "Pretorius, Nadine O."
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- ItemThe investigation and analysis of RAFT-mediated block copolymers in aqueous dispersed media(Stellenbosch : Stellenbosch University, 2007-12) Pretorius, Nadine O.; Sanderson, R. D.; McLeary, J. B.; Stellenbosch University. Faculty of Science. Dept. of Chemistry and Polymer Science.ENGLISH ABSTRACT: Polymers prepared via radical techniques are very common in our every day environment. The technique is however limited by a lack of control over the polymerization and an inability to produce block copolymers. Block copolymers have a significant number of potential applications in advanced materials and as a result are a field in which significant research is being conducted. Reversible Addition-Fragmentation chain transfer (RAFT) is a living free radical process that overcomes the disadvantages inherent in the traditional process. In this study the mediation behaviour of two inherently different RAFT agents was investigated by the “living” free radical polymerization of model monomers via the RAFT process in homogeneous and aqueous dispersed media with the focus on differentiating between the two types of agents. To ensure that the agents were comparable a new RAFT agent had to be prepared which has not previously been documented. The efficiency of the RAFT agents was compared in terms of rate effects, the predictability of the molecular weights of the polymers, the polydispersities of the polymers and their ability to allow block copolymer formation via sequential addition of monomers. Block copolymerizations were conducted by the addition of new monomer to the already existing RAFT end-capped chains. Monomer addition was done via three different approaches; namely shot addition, feed addition and pre-swelling (in the case of emulsions). Chromatographic analysis was conducted on the resulting block copolymers via liquid chromatography at critical conditions (LCCC), and its online coupling with size-exclusion chromatography (SEC) to obtain two-dimensional information on the differences in heterogeneity of their molecular distributions. Other analyses included dynamic light scattering analysis (DLS) and transmission electron microscopy (TEM). The detailed analysis enabled the understanding of the different products that are produced via the two different classes of RAFT agent. Potential causes for the differences are discussed and possible areas for future research are highlighted. The work presented here is the most detailed investigation of this class of polymerization to date and will provide new insight for researchers working in this vibrant and important research field.