Development of advanced methods for the analysis of star and highly branched polymers

Murima, Douglas (2020-03)

Thesis (PhD)--Stellenbosch University, 2020.

Thesis

ENGLISH ABSTRACT: Branched polymers are a unique class of materials with broad applications in fields such as automobile parts, textiles, lubricants, packaging, medicine, construction, soil binders in agriculture, and so on. Much of their attractive properties when compared to their linear counterparts are a result of variations in chemical composition, molar mass and architectural distributions. Branching in polymers may exist naturally (e.g. polysaccharides, natural rubber) or deliberately induced (e.g. in synthetic rubber and packaging materials from polyolefins, rheology modifiers). Advances in the synthesis of branched polymers with complex architectures for various targeted applications have continued to add to the growing need of more advanced characterization methods for structure-property correlations. In this current work, the development of various advanced methods for separation and characterization of lowly and highly branched polymers with distributions that include molar mass, degree of branching and chemical composition were investigated. Monodisperse star-branched polystyrenes with varying numbers of arms (3, 4, and 6 arms) provided a clean model systems for the analysis of crude star-branched polybutadienes with 3 and 4-arms, miktoarm-polystyrene-polyisoprene, and then a more complex hyperbranched Bd-PS. The first experimental part described the preparation of 3-arm, 4-arm and 6-arm star polystyrenes from multi-armed RAFT agents. Here, for the first time, the comprehensive characterization of star functionality (number of arms) via triple detector SEC and correlating with average functionalities determined by offline 1H-NMR and comparing the resolution of different chromatographic techniques was presented. The second part extended the comparison between the separation capabilities of HPLC in both 1D and 2D modes to resolve highly branched block copolymers. The novelty of the work was highlighted regarding the comprehensive analysis of hyperbranched block copolymers using liquid chromatographic techniques in combination with spectroscopic techniques and remarkable correlations were established. The third experimental part of this work discussed, for the first time, the application of multidetector Thermal field-flow fractionation as a channel-based separation technique for determining polymer conformations from Mark-Houwink plots and the degree of branching using functionality plots for a set of 3-, 4-, and 6-arm star polystyrenes, and a more complex hyperbranched polybutadiene-polystyrene (PBd-PS) copolymer in a single experiment.

AFRIKAANSE OPSOMMING: Vertakte polimere is 'n unieke klas materiale met breë toepassings in velde soos motoronderdele, tekstiele, smeermiddels, verpakking, medisyne, konstruksie, grondbinders in die landbou, ensovoorts. Baie van hul aantreklike eienskappe in vergelyking met hul lineêre eweknieë is die resultaat van variasies in chemiese samestelling, molmassa en argitektoniese verdeling. Vertakkings in polimere kan natuurlik bestaan (b.v. polisakkariede, natuurlike rubber) of doelbewus veroorsaak word (b.v. in sintetiese rubber en verpakkingsmateriaal van poli-olefiene, reologie-modifiseerders). Die vooruitgang in die sintese van vertakte polimere met komplekse argitekture vir verskillende doelgerigte toepassings het steeds bygedra tot die groeiende behoefte aan meer gevorderde karakteriseringsmetodes vir struktuureienskap korrelasies. In hierdie huidige werk is die ontwikkeling van verskillende gevorderde metodes vir die skeiding en karakterisering van lae en sterk vertakte polimere met verspreidings wat molêre massa, die mate van vertakking en chemiese samestelling insluit, ondersoek. Monodisperse stervertakte polistireen met wisselende aantal arms (3, 4 en 6 arms) het 'n skoon modelstelsels voorsien vir die ontleding van ru-vertakte polibutadiëne met 3 en 4-arms, miktoarm-polistireen-poli-isopreen, en dan nog 'n meer komplekse hipervertakte Bd-PS. Die eerste eksperimentele deel het die bereiding van 3-arm-, 4-arm- en 6-arm-ster-polistireen van mult-arm RAFT-middels beskryf. Hier is die eerste keer die uitgebreide karakterisering van sterfunksionaliteit (hoeveelheid arms) via die drievoudige detector SEC en korreleer met die gemiddelde funksionaliteite wat deur offline 1H-NMR bepaal is, en die resolusie van verskillende chromatografiese tegnieke vergelyk. Die tweede deel het die vergelyking tussen die skeidingsvermoëns van HPLC in beide 1D- en 2D-modusse uitgebrei om hoogs vertakte blokkopolimere op te los. Die nuwigheid van die werk is uitgelig met betrekking tot die uitgebreide analise van hipervertakte blokkopolimere met behulp van vloeistofchromatografiese tegnieke in kombinasie met spektroskopiese tegnieke en merkwaardige korrelasies is vasgestel. Die derde eksperimentele deel van hierdie werk het vir die eerste keer die toepassing van multidetektor termiese veldvloei-fraksionering bespreek as 'n kanaalgebaseerde skeidingstegniek vir die bepaling van polimeerkonformasies vanaf Mark-Houwink grafieke en die mate van vertakking deur gebruik te maak van funksionele plotte vir 'n stel van 3-, 4- en 6-arm ster-polistireen, en 'n meer komplekse hipervertakte polibutadiëen-polistireen (PBd-PS) -kopolymeer in 'n enkele eksperiment.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/107895
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