Doctoral Degrees (Chemistry and Polymer Science)

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Browsing Doctoral Degrees (Chemistry and Polymer Science) by Subject "Aliphatic compounds"

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    Multidimensional analytical techniques for the characterization of aliphatic polyesters
    (Stellenbosch : Stellenbosch University, 2013-03) Pretorius, Nadine Odette; Pasch, Harald; McLeary, J. B.; Stellenbosch University. Faculty of Science. Dept. of Chemistry and Polymer Science.
    ENGLISH ABSTRACT: Complex polymers are defined by their distributive properties with respect to molecular weight, chemical composition, functionality and molecular topology. As a result, polymer properties are very frequently determined not only by one of these entities but by the correlation of two or more distributions. Aliphatic polyesters are industrially implemented in high performance coatings, paints and varnishes. However, it is typically difficult to correlate the resulting properties with the synthesis parameters as these polymers vary in reactivity and application properties. Copolyester synthesis by direct polyesterification is often assumed to produce randomized products due to the mechanisms involved in stepwise polymerization. The formation of cyclic products by intramolecular reactions of hydroxyl (OH) and carboxylic (COOH) functional groups, sidereactions such as transesterification, alcoholysis, and ester-ester interchange allow even further randomization, enabling a highly complex system. Therefore, in addition to molecular weight distribution, polyesters exhibit chemical composition, functionality type as well as branching distributions, classifying them as complex polymeric systems. The different methods of polymer chromatography in combination with sophisticated spectrometry techniques are useful tools for enabling the full description of the molecular heterogeneity of these complex polyesters. The present study entails method development of different modes of chromatography and mass spectrometry along with their combination, to facilitate the analysis of the various distributions of two model polyester systems, phthalic and maleic anhydride, respectively, in combination with propylene glycol. Gradient HPLC analysis enabled an oligomeric separation based on chemical composition of the respective anhydride/propylene glycol samples. Its off-line coupling to MALDITOF MS and ESI-QTOF MS revealed the presence of several distributions of varying endgroup functionality type and molecular weight distributions at different intervals throughout the polymerization. In addition, online gradient HPLC x size exclusion chromatography (2D-LC) was conducted to obtain the dual chemical composition-molecular weight (CCD-MWD) distribution. The combination of the different coupling techniques provided the opportunity to a more in-depth analysis of the structure-property relationships.