Abstract
New equipment designed to measure the effect of pressure and isotopic substitution on liquid/liquid equilibria in polymer/solvent systems is described. The phase separation is detected by monitoring low-angle forward scattered light, together with simultaneous loss in transmitted light, from an He–Ne laser shining through the sample. Phase transitions can be induced by varying temperature/time and/or pressure/time profiles or by a combination of such changes. The system operates at high precision (±0.001 K, ±0.002 MPa), and over wide temperature and pressure ranges (240≤T/K≤600, 0.01≤P/Mpa≤35). The temperature, pressure, and transmitted and scattered light intensities are digitally recorded, and the rate of change of the temperature and/or pressure used to induce the phase transition is under computer control. The system is being used to study the temperature, pressure, polymer molecular weight, and molecular weight distribution, and H/D dependences of phase equilibria for polystyrene (PS)/(CH3)2CO and PS/(CD3)2CO solutions. Sample results are reported. The pressure and molecular weight dependences of the coexistence curve, and their isotope effects, are large.
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