POLYMER DESIGN FOR PERVAPORATION MEMBRANES - INFLUENCE OF THE SOFT SEGMENT SIZE OF BLOCK-COPOLYMERS (POLYURETHANEIMIDES OR POLYUREAIMIDES) ON THEIR PERVAPORATION FEATURES

Three sets of new block copolymers PUI with increasing soft segment le ngths were obtained by a method which allows the control of the materi al structure by a step-by-step polycondensation: polyetherurethaneimid es (PEG-MDI-AP), polyetherureaimides (JFA ED-MDI-AP) and polyesteruret haneimides (PCL-MDI-AP) with soft block molecular weights in the range of 300-2000. At 30 degrees C, all the PUI exhibited selectivity towar ds ethanol during the pervaporation of EtOH/ethyl tert-butylether mixt ures close to the azeotropic composition and the PV fluxes were relate d to the polymer structure in a quantitative way. They were shown to v ary exponentially with the soft segment weight fraction in the case of PUL polyethers whereas linear relationships described the partial and total fluxes obtained with PUI polyesters. The second part of the inv estigations dealt with the influence of the soft segment length on the PV features of PUI at higher temperatures. Despite one particular pol ymer leading to a significant deviation from the usual behaviour, the PV mass transfer of both permeants in all the PUI investigated obeys a n Arrhenius type law in the temperature range of 30-60 degrees C. The activation energies could be related to the material structure qualita tively, showing an important decrease of these parameters for the poly mers with the longest soft segments.