Evaluation of nonradiative energy transfer as a means of probing polymer miscibility and polymer phase separation

The ability of nonradiative energy transfer (NRET) to probe polymer miscibility and polymer phase separation is discussed for blends of PVC and PMMA of various tacticity. The sensitivity of that fluorescence technique depends on the range between the lower (total miscibility) and the upper value (complete immiscibility) of the ratio of the intensity emitted by naphthalene and anthracene (IN/IA) used to label PVC and PMMA, respectively. Although measurements of the lower limit are reproducible, determination of the upper limit is quite a problem, making uncertain the analysis of any system phase separated on a scale of at least 2-3 nm. At and above this dimension, solvent-cast PVC/PMMA blends appear to be completely miscible whatever the PMMA tacticity. That the IN/IA ratio of the PVC/PMMA blends changes with the tacticity of PMMA is interpreted as an effect of chain conformation on the probability of intermolecular interactions. For instance, the more rigid the PMMA is in relation to its tacticity, the more extended the intermolecular contacts with PVC see blend above the LCST does not lead to an increase in the IN/IA ratio great enough to detect phase separation. © 1990, American Chemical Society. All rights reserved.