KINETICS OF PHASE-SEPARATION - TRAPPING OF MOLECULES IN NONEQUILIBRIUM PHASES

When solutions of molecularly nonuniform polymers in single solvents are rapidly (1 K/s) cooled into the two-phase region, up to 20% of the polymer mass and 1.5% of the solvent molecules that would be found in the more dilute phase (sol) under equilibrium conditions are instead found in the more concentrated phase (gel). The higher molecular weight material of the equilibrium sol is preferentially incorporated into the nonequilibrium gel, with a capture probability increasing linearly with log M. Qualitatively the observations can be explained by the following consideration: For high cooling rates the polymer coils shrink so rapidly that the mobility of some chains no longer suffices for their withdrawal from the overlap region with others in order to become part of the sol phase. Quantitative calculations performed on the basis of this concept demonstrate that all experimentally observed features can be well reproduced if two (measurable, but presently unknown) parameters are adjusted. © 1990, American Chemical Society. All rights reserved.