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RESEARCH PRODUCT

Continuous fractionation and solution properties of PIB. I. Search for the best mixed solvent and first results of the continuous polymer fractionation

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To adopt a recently developed method for large scale fractionation (CPF = continuous polymer fractionation, a special kind of counter current extraction) to polyisobutylene (PIB), a systematic search for the best mixed solvent was performed. For this purpose, the essential parts of the phase diagrams solvent/nonsolvent/PIB were determined for 21 mixed solvents by cloud-point measurements; with eight systems of special interest, the molecular weight distributions of the polymers contained in the coexisting phases were also studied. On the basis of these experiments and of considerations concerning additional criteria for the performance of the continuous counter current extraction, the mixed solvent toluene/methyl ethyl ketone was chosen. First experiments with a PIB sample of Mw = 420,000 g/mol and a molecular nonuniformity U = (Mw/Mn) − 1 of 2.3 yielded two high molecular weight fractions Mw = 1.1 × 106 and 0.6 × 106 resp., with U = 0.3 on a 100 g scale upon the application of four CPF steps.