Abstract
The influence of pressure on a lower critical solution temperature is much more pronounced than on an upper critical solution temperature. Accordingly it is possible to control phase separation at a LCST phase boundary under isothermal conditions by merely adjusting the pressure on the system. An apparatus has been constructed to investigate the isothermal fractionation of polyisobutene in which precipitation is controlled by pressure. Two samples of polyisobutene of Mv=1.76×106 and 9.0×104 have been fractionated in isopentane solution so as to yield up to six and nine fractions respectively. The integral molecular weight distribution curves thus obtained are compared with those obtained from conventional fractionations at an UCST. The sensitivity of the method is poor with regard to the separation of low molecular weight fractions and degradation occurs at the higher temperatures to an appreciable extent.
