POLYMER ADDITIVES MIXTURE ANALYSIS USING PULSED-FIELD GRADIENT NMR-SPECTROSCOPY

The analysis of mixtures is a problem commonly faced in analytical che mistry. In this work, pulsed-field gradient NMR (PFG-NMR) experiments were used to analyze mixtures of polymer additives and simple polymer solutions. PFG-NMR experiments were also utilized to determine diffusi on coefficients of the individual components of a mixture and in this way facilitate resonance assignments. This strategy is particularly us eful for molecules containing isolated protons that are not amenable t o the standard two-dimensional NMR experiments based on J-coupling. PF G-NMR was also used to edit the NMR spectra of polymer solutions by el iminating the resonances of fast-diffusing components such as low mole cular weight additives or residual solvent. Diffusion ordered spectros copy (DOSY) was used for the analysis of the PFG-NMR data. The DOSY me thod produces a two-dimensional spectrum that correlates chemical shif t with the calculated diffusion coefficient, and simplifies the analys is of many complex mixtures. For well resolved resonances, the correct diffusion coefficient is unambiguously determined. The DOSY analysis was able to resolve the diffusion coefficients of most of the componen ts in the mixtures examined. However, in some cases of overlapped reso nances and components with similar diffusion coefficients, a single di ffusion coefficient was determined which was the weighted average of t he two components.