Coupling of thermal field-flow fractionation and FTIR spectroscopy for the fractionation and analysis of complex polymers

Radebe, Nonkululeko Winnie (2017-12)

Thesis (MSc)--Stellenbosch University, 2017.


ENGLISH ABSTRACT: The fast-paced growth and production of complex polymers has accelerated the need for advancement in characterization techniques. The structural complexity of polymers is described using the concept of molecular heterogeneity in molar mass, chemical composition, molecular architecture. The task of characterizing complex polymeric materials is a challenge, and has accelerated the need for hyphenated techniques that provide adequate information regarding the different microstructure distributions. The increased use of hyphenated techniques has prompted the development of online coupling of thermal field flow fractionation (ThFFF) and Fourier transform infrared spectroscopy (FTIR). ThFFF is a powerful channel-based fractionation tool for microstructure analysis of complex polymers as it has the ability to separate according to both molar mass and composition in a single experiment. FTIR, coupled to a separation technique, provides concentration profiles as well as detailed chemical structure information of macromolecules as a function of ThFFF elution volume. The presented coupled method will significantly decrease the time needed for ThFFF-FTIR as compared to collecting fractions from ThFFF separation and subsequent offline analysis by FTIR. The inherent problem with the online coupling of ThFFF to FTIR is the combination of strong solvent signals and relatively low sample concentration necessary for ThFFF separation. To overcome this, a specialized flow cell was constructed and a mathematical solvent suppression routine was used to subtract the solvent signals. In the present study, the setup of the method as well as data treatment and example measurements are presented. Blends of polystyrene (PS) and poly (methyl methacrylate) (PMMA) as well as copolymers of styrene and methyl methacrylate (SMA) are analyzed and quantified using the method. By selecting spectral bands that are unique to each analyte, the distribution of the individual analyte components across the elution profile are measured and presented. Even when quantification is not possible, the technique can be used as a means of qualitative analysis, as seen for styrene-acrylonitrile (SAN) copolymers. In one integrated procedure, ThFFF -FTIR is shown to provide detailed microstructural characterization of complex multicomponent samples.

AFRIKAANSE OPSOMMING: Die vinnige groei en produksie van komplekse polimere het die behoefte aan vooruitgang in karakteriseringstegnieke versnel. Die strukturele kompleksiteit van polimere word beskryf deur gebruik te maak van die molekulêre heterogeniteit konsept in molêre massa, chemiese samestelling, molekulêre argitektuur. Die taak om hierdie polimeerstowwe te karakteriseer, is 'n uitdaging en het die behoefte aan koppeltekstegnieke versnel wat voldoende inligting verskaf oor die verskillende mikrostruktuurverdelings. Die toenemende gebruik van koppeltekens het daartoe gelei dat die ontwikkeling van aanlynkoppeling van termiese veldstroomfraktasie (ThFFF) en Fourier-transform infrarooi spektroskopie (FTIR) ontwikkel is. ThFFF is 'n kragtige kanaalgebaseerde breukinstrument vir mikrostrukture-analise van komplekse polimere, aangesien dit die vermoë het om volgens 'n enkele eksperiment volgens beide molêre massa en samestelling te skei. FTIR, gekoppel aan 'n skeidingstegniek, verskaf konsentrasieprofiele sowel as gedetailleerde makromolekule chemiese struktuurinligting as 'n funksie van elueringsvolume.

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