Innovative spectroscopic and chromatographic techniques for the analysis of complex polyolefins prepared by metallocene catalysis

Graef, Sven Markus (2002-12)

Thesis (PhD)--Stellenbosch University, 2002.

Thesis

ENGLISH ABSTRACT: The study focused on the analysis of a variety o f synthesised tailored copolymers. During the investigation o f the samples new and innovative analytical techniques were developed to be able to identify the presence of certain predicted or expected copolymerisation products. Emphasis was placed on the versatility of CRYSTAF as a method for the analysis of semi-crystalline copolymers. Changes in the crystallisation temperature were used as an indicator, while the type o f method, solvent and sample weight served as variables in the system. The percentage comonomer content distribution for an unknown sample was determined from the standard curve plotted with the aid o f copolymers with known comonomer content. Ethylene/higher a-olefin and propylene/higher a-olefm copolymers were synthesised by means o f a metallocene precatalyst. In both cases, NMR spectroscopy, DSC, GPC, and CRYSTAF were used as analytical tools. In the ethylene series it was shown that the sample mixture was homogenous in the molar mass axis (GPC) but not in the chemical composition axis (CRYSTAF) regarding the comonomer content. For the propylene series, an increase in stereoerrors was observed by NMR and this was correlated with crystallisation on heating a DSC for the range o f copolymers. In the case where ethylene/methyl methacrylate block copolymers were synthesised using metallocene precatalyst, novel detection and separation methods were used and developed. This included the use o f CRYSTAF fitted with a carbonyl filter, high temperature gradient HPLC and high temperature liquid chromatography under critical conditions (LCCC). The last two techniques were the first where separation could be achieved with samples only dissolving at high temperature. All previous mentioned techniques, as well as the coupling of FTIR to GPC and high temperature gradient HPLC via LC-Transform revealed that the samples consisted o f varying ethylene and MMA block lengths.

AFRIKAANSE OPSOMMING: Die doelstelling van die navorsing was die analise van spesiaalvervaardigde kopolimere. Nuwe analitiese tegnieke is vir die bevestiging van sekere voorgestelde kopolimerisasie-produkte ontwikkel. Klem is gelê op die veelsydigheid van CRYSTAF as ’n metode vir die analise van gedeeltelik-kristallyne kopolimere. Veranderinge in die kristallisasie-temperature is as respons gebruik, terwyl die metode van sintese, die oplosmiddel en die hoeveelheid monster as veranderlikes in die sisteem beskou is. ‘n Standaardkurwe vir komonomeerinhoud is opgestel met behulp van kopolimere met ‘n bekende komonomeerinhoud. Hierdie kurwe is gebruik om die komonomeerinhoudsverspreiding van onbekende monsters te bepaal. Etileen/hoër a-olefien- en propileen/hoër a-olefien-kopolimere is met behulp van ‘n metalloseen pre-katalis gesintetiseer. In beide gevalle is KMR spektroskopie, DSC, GPC en CRYSTAF gebruik om die analises uit te uitvoer. Met verwysing na komonomeerinhoud is daar in die geval van die etileenreeks bevind dat die monstermengsel homogeen is met betrekking tot die molere massa, maar nie met betrekking tot die chemiese samestelling nie. Vir die propileenreeks is ’n verhoging in die stereofoute met behulp van KMR waargeneem. Dit is gekorrelleer met kristallisasie weens verhitting tydens DSC-bepalings vir die reeks kopolimere. In die geval van die sinteses van etileen/metielmetakrilaat-blokkopolimere met metalloseen as pre-katalis, moes nuwe waamemings- en skeidingstegnieke ontwikkel word. Dit het die gebruik van CRYSTAF met ’n karbonielfilter, hoetemperatuurgradient- HPLC en hoë-temperatuurvloeistofchromatografie onder kritiese toestande ingesluit. Laasgenoemde twee tegnieke het vir die eerste keer skeiding van monsters wat net by hoe temperature oplos, moontlik gemaak. Bogenoemde tegnieke, sowel as die koppeling van FTIR met GPC en hoë-temperatuur-gradient-HPLC via LC-transformasie het getoon dat die monsters etileen- en MMA-blokke met verskillende lengtes bevat het.

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