COAGULATION OF POLY(P-PHENYLENE BENZOBISOXAZOLE) IN POLYPHOSPHORIC ACID USING AQUEOUS AND NONAQUEOUS SOLUTIONS

Diffusion of aqueous and nonaqueous coagulants into lyotropic/nematic solutions of poly(phenylene benzobisoxazole) in polyphosphoric acid us ing fluorescence microscopy is reported. The fluorescence microscopy t echnique offers advantages in that the experiment is independent of th e coagulant and the experiments can be performed in a front surface mo de so that optically thin samples are not required. The diffusion proc ess is modeled as Case II diffusion as described by Crank and Park. Th e apparent diffusion coefficients are found to range from similar to 2 X 10(-6) cm(2)/s to similar to 2 X 10(-7) cm(2)/s for aqueous and non aqueous coagulants. The apparent diffusion coefficients can be varied by several orders of magnitude (e.g., down to similar to 3 X 10(-10) c m(2)/s) by varying the concentration of polyphosphoric acid in the coa gulant. (C) 1995 John Wiley & Sons, Inc.