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Stellenbosch, South Africa

Pretorius N.O.,Stellenbosch University | Rode K.,Fraunhofer Institute for Structural Durability and System Reliability | Simpson J.M.,Kansai Plascon Research Center | Pasch H.,Stellenbosch University
Analytica Chimica Acta | Year: 2014

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) was used in conjunction with size exclusion chromatography (SEC) to investigate a model polyester system based on phthalic anhydride-1,2-propylene glycol. The polyesters were synthesized with a 30% molar excess of glycol, with kinetic samples being removed during different intervals of the polyesterification reaction. SEC was used to track the course of the reaction by determining the molecular weight and molecular weight distributions before subsequent off-line coupling with MALDI-TOF MS as a selective detection method to determine the chemical composition, identify the functionality type distributions as well as assist in assigning structural conformations. Mass spectrometry analysis proved to be a highly effective tool to facilitate the identification of the narrowly dispersed fractions obtained from the chromatographic separations as well as serve as a core method to investigate the heterogeneous nature of the bulk kinetic samples. Through the hyphenation of these sophisticated polymer characterization techniques, information on the molecular heterogeneity of the model polyesters, showing a complex variety of possible distributions, was obtained. © 2013 Elsevier B.V.

Pretorius N.O.,Stellenbosch University | Rhode K.,Fraunhofer Institute for Structural Durability and System Reliability | Simpson J.M.,Kansai Plascon Research Center | Pasch H.,Stellenbosch University
Analytical and Bioanalytical Chemistry | Year: 2014

The combination of gradient HPLC, 2D chromatography, and MALDI-TOF MS facilitated the analysis of the various distributions of phthalic acid/propylene glycol-based model polyesters. Investigations of kinetic samples taken at various reaction times highlighted the subsequent differences at various stages of the polyesterification reaction in terms of molecular weight, chemical composition, and endgroups. Normal-phase gradient-HPLC analysis successfully enabled an oligomeric separation of the respective samples. Peak-splitting behavior in early eluting peaks suggested that the separation was affected by a combination of factors and not solely based on chemical composition, functionality type or degree of polycondensation. Two-dimensional chromatography provided the link between chemical composition and molecular weight distribution, confirming that the first dimension gradient HPLC separation was based on chemical composition with increasing degree of oligomerization in the second dimension. The off-line coupling of LAC with MALDI-TOF MS provided structural details in combination with improved molecular weight determination of the more homogeneous LC fractions. The study indicated that all aspects related to the model saturated anhydride system should be considered in the case of copolyester synthesis to produce industrial type polyester resins. It was shown that the present multidimensional approach provided most comprehensive structural information on the polyester system. [Figure not available: see fulltext.] © 2014 Springer-Verlag Berlin Heidelberg.

Charlton D.,Kansai Plascon Research Center | Keulder L.,Kansai Plascon Research Center | Bisschoff J.,Kansai Plascon Research Center
European Coatings Journal | Year: 2013

A new test method uses pigments in an appropriate paint and provides accurate and repeatable measurements expressed as Cielab color shifts. Bismuth vanadates are high quality yellow inorganic pigments used in both solvent-based and water-based paint systems. They are produced by two processes; either a wet process or by high-temperature calcination. One example of their production is by mixing solutions of bismuth nitrate, ammonium or sodium vanadate, sodium molybdate and nitric acid. Precipitates from the oxides and hydroxides are formed and washed until they are free of salt. The chemical properties of these pigments include insolubility in water and alkaline material. However, in strongly alkaline materials they may show instability and the color may change. At pH values below two the pigments might solubilise, but that will depend on the stabilization of the pigment. Unstabiused bismuth vanadate pigments will also undergo photochromism when exposed to intense radiation.

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