FRACTIONATION OF A STATISTICAL COPOLYMER IN A DEMIXING-SOLVENT SYSTEM- THEORY AND EXPERIMENT

It has been shown that, under specific conditions, a demixing-solvent fractionation according to chemical composition can be applied to stat istical copolymers. Formally, identical expressions have been derived for the distribution of a copolymer between coexisting phases in preci pitation (sol-gel) and demixing-solvent fractionations. Theory predict s that the effects of molar mass and chemical composition cannot be se parated in either of the phase-equilibrium fractionations. With demixi ng solvents, the partition coefficient depends steeply on copolymer co mposition, which enables one, e.g., to separate homopolymers from a bl end. Multistep demixing-solvent fractionation of a copolymer may proce ed only in specific cases, e.g., immediately below the maximum of the coexistence curve. A feasibility study was performed with a chemically heterogeneous statistical copolymer of styrene and 2-methoxyethyl met hacrylate; the experimental results have confirmed the theoretical pre dictions.