EXCIMER FLUORESCENCE AS A PROBE OF MISCIBILITY IN STYRENE COPOLYMER BLENDS

The miscibility of styrene-alt-maleic anhydride (SMA) and a series of styrene-acrylonitrile (SAN) copolymers in blends with either PMMA or PVC were examined by fluorescence and FTIR spectroscopic techniques. In the case of the alternating copolymer intra-molecular excimer formation is precluded and changes in the excimer/monomer fluorescence intensity (I(E)/I(M)) reflect changes in the amount of inter-chain excimer formation. The value of I(E)/I(M) in blends, therefore, provides a sensitive measure of phase separation (miscibility). In the case of the acrylonitrile copolymers the I(E)/I(M) of the blend had to be corrected to account for intra-molecular excimers formed between adjacent chromophores in the SAN. These results compared favourably with observed frequency shifts in the phenyl C-H out-of-plane bend (approximately 700 cm-1).