Fluorescence of Vinyl Aromatic Polyelectrolytes: Effects of Conformation, Concentration, and Molecular Weight of Sodium Poly(styrenesulfonate)

Conformational behavior of atactic sodium poly(styrenesulfonate) has been investigated by the use of fluorescence spectroscopy. Measurement of the excimer to monomer fluorescence intensity ratio, I_E/Im, provides information relating to specific conformational populations in vinyl aromatic polymers. The overall size of the polyelectrolyte coils was varied extensively through control of ionic strength of the solvent, and the influence of the overall conformation of the polyelectrolyte on I_E/I_Mwas monitored. As the shape of the chain changes from a highly extended, rodlike form to a loose coil, was found to be approximately constant, implying that local bond conformations are almost invariant. Increased molecular weight was found to increase I_E/I_Min a manner that cannot be explained solely on the basis of end effects. The concentration dependence of I_E/I_M was similar to that observed in polystyrene: no effect is seen for 0.01 ≤ c ≤ 2 g/L, and above 2 g/L I_E/I_Mincreases only very gradually. Absorbance spectra were recorded and found to exhibit slight sensitivity to conformational changes.