Excimer fluorescence as a molecular probe of polymer blend miscibility: 8. Polymeric and glassy solvent host matrices

• Published in: Polymer (Guilford) 1988-09, Vol.29 (9), p.1625-1634
• Main Authors: Tao, William C., Thomas, Jule W., Frank, Curtis W.
• Format: Article
• Language: English
• Subjects: blends; excimer fluorescence; miscibility; molecular probe
• ISSN: 0032-3861; 1873-2291
• DOI: 10.1016/0032-3861(88)90274-1

The effects of solubility parameter differences between the guest polymer and the host matrix and of guest molecular weight on the thermodynamic miscibility and chain configuration of poly(2-vinylnaphthalene) (P2VN) dispersed in polymeric or glassy solvent hosts are investigated using excimer fluorescence. For P2VN blends with a series of poly(alkyl methacrylates) in which the difference in the guest and host solubility parameters is minimized, the small increase in the excimer to monomer fluorescence ratio, I D I M , with increasing P2VN molecular weight can be rationalized by a one-dimensional energy migration model proposed by Fitzgibbon and Frank. The results indicate the possibility of small-scale phase separation or local coil contraction for P2VN with molecular weight greater than 21 000. As the thermodynamic interaction between the guest and polymeric host is altered towards immiscibility, I D I M can be related to the extent of intermolecular aggregation in the blend. To study the efficiency of intramolecular energy migration independent of intermolecular association and free of casting solvent effects, we chose a host system consisting of a series of monomeric glassy solvents. The rate of energy transfer is investigated by transient fluorescence and treated by a one-dimensional model developed by Fredrickson and Frank. The results are in excellent agreement with independently measured photostationary-state fluorescence ratios.