Reversible addition-fragmentation transfer polymerization in heterogeneous aqueous media

McLeary, James Breton (2004-04)

Thesis (PhD)--Stellenbosch University, 2004.

Thesis

ENGLISH ABSTRACT: The study presented in this dissertation had as primary aim to develop pathways to heterogeneous aqueous polymerizations that had living characteristics. To this end, the reversible addition fragmentation chain transfer (RAFT) process was investigated in predispersed and ab initio emulsions as well as homogeneous media. The synthesis of RAFT agents was carried out. The compounds prepared provided varied behaviour in reaction. In situ IH nuclear magnetic resonance (NMR) increased understanding of homogeneous RAFT mediated polymerizations. The early behaviour of RAFT mediated polymerizations led to the definition of initialization; a period before pre-equilibrium in a polymerization where degenerate behaviour occurs. Stable miniemulsion preparation methods were developed that provided living polymer latexes using high surfactant concentrations. The effect of surfactant concentration on particle size and latex stability was investigated. Living polymer characteristics were shown by the use of size exclusion chromatography, and 2- dimensional chromatography conclusively showed block polymer formation. In situ NMR spectroscopy of emulsions in deuterated water was used to provide evidence on the role of initiator solubility in polymerization. Secondary nucleation in high surfactant concentration miniemulsions systems was investigated using both particle size and molar mass analysis techniques and a means of eliminating secondary particle nulceation was shown through the use of aqueous phase radical traps. The role of the RAFT agent used in the polymerization was shown to be significant in determining the extent to which multiple polymer distributions formed in the polymerization in that radical exit from particles was affected. Finally, a new form of emulsion polymerization, which has been termed proto-seeded emulsion, has been developed. The proto-seed latex is formed by using a monomer whose polymer has chain length dependent water solubility. This process allows ab initio RAFT mediated emulsion polymerization to be conducted successfully without transport of RAFT agents in heterogeneous media.

AFRIKAANSE OPSOMMING: Die primerê doel in hierdie dissertasie is die ontwikkeling van roetes na heterogene water-gebaseerde polimerisasies met lewende eienskappe. Om hierdie doel te bereik is die omkeerbare addisie fragmentasie ketting oordrag proses (eng reversible addition fragmentation chain transfer (RAFT)) ondersoek in vooraf verspreide en direkte emulsies sowel as homogene media. Die sintese van RAFT agente is uitgevoer. Die verbindings wat voorberei is het verskillende einskappe in reaksies getoon. In situ IH kern magnetiese resonansie (KMR) het die kennis en begrip van homogene RAFT polimerisasies uitgebrei. Die vroeë gedrag van RAFT polimerisasies het tot die definisie van inisialisasie gelei; 'n periode voor die pre-ekwilibrium in 'n polimerisasie waartydens "degenerate" gedrag plaasvind. Stabiele miniemulsie voorbereidings metodes is ontwikkel wat lewende polimeer latekse verskaf het met gebruik van hoë seep konsentrasies. Die effek van seep konsentrasie op partikel grootte en lateks stabilitiet is ondersoek. Lewende polimeer eienskappe is bewys deur gebruik te maak van grootte-uitsluiting vloeistof chromatografie, en 2-dimensionele chromatografie het duidelik blok-polimeer vorming gewys. In situ KMR spektroskopie van emulsies in gedeutereerde water is gebruik om bewys te lewer van die rol van initieerder-oplosbaarheid in polimerisasie. Sekondêre nukleasie in hoë seep konsentrasie miniemuisie sisteme is ondersoek met die gebruik van beide partikel grootte sowel as molêre massa analise tegnieke. 'n Metode om sekondêre partikels te verhoed is verskaf deur gebruik te maak van waterfase radikaal lokvalle. Die rol van die RAFT agent in die polimeerisasie is beduidend in die graad van vorming van meer as een polimeer distribusie in die sin dat radikal uitgang van partikels beinvloed was. Ten slotte is 'n nuwe vorm van emulsie polimeerisasie ontwikkel wat proto-gesaaide emulsie genoem is. Die proto-gesaaide lateks is gevorm deur gebruik te maak van 'n monomeer waarvan die polimeer water-oplosbaarheid afhanklik is van die kettinglengte. Die proses laat ab initio RAFT emulsie polimerisasie toe om suksesvol uitgevoer te word sonder die vervoer van RAFT agente in heterogene media.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/53760
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