Semi-quantitative analysis of the monomer composition in co-polymer microgels using solid state Raman and NMR spectroscopy

A series of colloidal microgels have been prepared by surfactant-free emulsion polymerisation (SFEP) based on the N-isopropylacrylamide (NIPAM) monomer. 4-Vinylpyridine (4-VP) and butylacrylate (BuA) have been used as co-monomers. Co-polymer poly(NIPAM/4-VP) and poly(NIPAM/BuA) have been prepared with various monomer ratios, ranging from pure poly( NIPAM) to pure poly(BuA)/poly(4-VP). Freeze-dried samples of the microgels have been analysed by solid state ( ss) Raman and NMR (Nuclear Magnetic Resonance) spectroscopy to investigate the monomer composition in the copolymer microgels. Spectral data have been analysed graphically and also statistically. Spectroscopic measurements have shown that co-polymerization has occurred. The graphical and statistical analysis of the spectroscopic data for both co-polymer microgels, enables the semi-quantitative measurement of the percentage incorporation of co-monomers (4-VP/BuA) in the co-polymer microgels. A good correlation exists between the Raman and NMR results, however, Raman spectroscopy is much less time consuming ( Raman spectral acquisition time is less than 10 minutes) and the measurements are easy to make and very small quantities (less than 1 mg) of the sample are required. This compares with the experimental measurements of similar to 72 hours and 100-200 mg of sample that are required for the NMR experiments.