Multidimensional fractionation of complex polymers by comprehensive online-coupled thermal field-flow fractionation and size exclusion chromatography.

Viktor, Zanelle (2020-12)

Thesis (PhD)--Stellenbosch University, 2020.

Thesis

ENGLISH ABSTRACT: The comprehensive characterization of complex polymeric materials remains a primary objective in research and industry. It is important to understand the molecular heterogeneity of complex polymeric materials and to establish correlations between the structure and the physical properties of a given polymeric material as it influences the end-use application thereof. Polymeric materials are distributed with regard to multiple molecular properties e.g. molecular mass, chemical composition and molecular topology (such as branching, microstructure and functionality). Due to the molecular complexity of polymeric materials, characterization and separation of the polymer with regard to its various distributions remains a major challenge for the analytical scientist. As a result, new analytical approaches have been developed over the years as well as advancing the capabilities of existing analytical techniques. In recent years, field-flow fractionation (FFF), a channel-based separation technique, has emerged as a suitable analytical method for the fractionation and characterization of complex polymers. FFF has been shown to be selective towards different molecular properties and is capable of providing comprehensive molecular distribution information. Thermal field-flow fractionation (ThFFF) and asymmetric flow field-flow fractionation (AsFlFFF) are two of the main sub-techniques of FFF used for polymer characterization. FFF is a well suited analytical technique to be used in either a multidetector hyphenation configuration or in a multidimensional configuration to address the characterization of the multiple molecular distributions present in a complex polymeric material. In the first part of the present research, a comprehensive online multidimensional analytical approach has been developed for the characterization of complex polymers. ThFFF, an analytical technique that has been shown to be sensitive towards chemical composition and topology, has been coupled to size exclusion chromatography (SEC), which separates based on the hydrodynamic size of the analyte molecules. To illustrate the capabilities of the developed ThFFF X SEC, poly(styrene)-b-poly(methyl methacrylate) block copolymers were separated and characterized. It was shown that in a single analysis, detailed molecular information (chemical composition and molecular mass distribution) as well thermal and translational diffusion information could be obtained. To further demonstrate the capabilities of the multidimensional method it was shown that in instances where separation is less than ideal, valuable information is still obtainable by hyphenation with information-rich detectors to ThFFF X SEC. In addition to the developed ThFFF X SEC technique, a method was developed that successfully separated poly(methyl methacrylate) (PMMA) according to tacticity using AsFlFFF. The solution behaviour of syndiotactic-, atactic- and isotactic PMMA with similar molecular masses was investigated in solvents with different thermodynamic properties. It was shown that by careful selection of the carrier liquid and channel temperature, microstructure-based separation can be achieved in AsFlFFF.

AFRIKAANSE OPSOMMING: Die karakterisering van komplekse polimere bly ‘n primêre doel in die veld van navorsing asook in die nywerheid. Dit is van belang om die molekulêre heterogeniteit van komplekse polimere te verstaan en die korrelasie tussen die struktuur en die fisiese eienskappe van ‘n gegewe polimeermateriaal te bepaal, aangesien dit die eindtoepassing daarvan beïnvloed. Komplekse polimere het verspreidings in veelvuldige molekulêre eienskappe bv. molekulêre massa, chemiese samestelling en molekulêre topologie (soos vertakings, mikrostrutuur en funksionaliteit). As gevolg van die molekulêre kompleksiteit van polimeermateriale, bly die karakterisering en skeiding van die polimeermateriaal ten opsigte van sy verskillende verspreidings ‘n uitdaging. In ‘n poging om dié uitdaging aan te spreek, word óf nuwe analitiese metodes ontwikkel óf die vermoë van bestaande analitiese metodes word verbeter. ‘n Voorbeeld van ‘n nuwe analitiese metode wat in die afgelope jare ontwikkel is, is veldvloei-fraksionering (FFF). FFF is selektief vir die verskillende molekulêre eienskappe en is instaat daarvan om gedetailleerde inligting rakende die molekulêre verspeidings, wat teenwoordig is in polimeermateriale, the voorsien. FFF is ‘n gepaste analitiese tegniek wat die vermoë het om aan veelvoudige detektore gekoppel te kan word of dit kan selfs in ‘n multi-dimensionele konfigurasie gekoppel word met ander analitiese tegnieke om die molekulêre verdelings van polimeermateriale te karakteriseer. In die eerste deel van die navorsing wat aangebied is, is 'n uitgebreide aanlyn multi-dimensionele analitiese protokol ontwikkel vir die karakterisering van komplekse polimere. Termiese veldvloei-fraktionering (ThFFF), wat sensitief is vir chemiese samestelling en topologie, is gekoppel aan grootte uistluitings chromatografie (SEC), wat die analietmolekules skei op grond van hulle hidrodinamiesegrootte. Om die potensiaal van ThFFF X SEC te illustreer, is poli(stireen)-b-poli(metiel metakrilaat) blok-kopolimeer geskei en gekarakteriseer. Die resultate het getoon dat in 'n enkele analiese gedetailleerde molekulêre inligting (chemiese samestelling en molekulêre massa verspreiding) sowel as termiese en normale diffusie-inligting verkry kon word. Daarbenewens is aangetoon dat met selektiewe deteksie, waardevolle inligting steeds bekombaar is in die geval van onvoldoende skeiding van ‘n monster, deur inligtingryke detektorete koppel aan ThFFF X SEC. ‘n Voorbeeld vansoos detektor is ultraviolet (UV). In die tweede deel van die navorsing wat aangebied is, is die skeidingsvermoë en selektiwiteit van asimmetriese vloei veldvloei-fraktionering (AsFlFFF) gedemonstreer. Die retensie gedrag van sindiotaktiese, ataktiese en isotaktiese poli(metiel metakrilaat) van soortgelyke molekulêre massas in oplosmiddels met verskillende termodinamiese eienskappe is ondersoek. Daar is aangetoon dat deur die noukeurige seleksie van die dravloeistof en die temperatuur van die kanaal, mikrostruktuur-gebaseerde skeiding in AsFlFFF verkry kan word.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/109155
This item appears in the following collections: