Executive Summary : | Polymeric membranes with enhance mass-transport and solute selectivity are highly anticipated for liquid separation. Unlike conventional separation processes (distillation, evaporation), membrane based liquid separation processes perform separation in liquid phase without changing the phase of desired solutes. To enable membrane-based separation of a large-scale unit operation, membranes with high mass transport and solute selectivity (permeability-selectivity trade off) becomes essential to process large volume of liquids over realistic membrane area. For enhancing the mass-transport, first-hand principles are (i) tailor made microporosity and (ii) downsizing the thickness of active separating membrane layer in the nanoscale dimensions for lesser resistance. Porous materials with well-defined pores become choice of membrane material for high mass transport, for example metal-organic frameworks (MOFs), porous coordination polymers, covalent organic frameworks (COF), and porous organic cages. COF membranes grown at the interface of two different immiscible solvents using interfacial chemistry, and showed enhanced mass transport, but the approach is limited by long reaction time, low lateral size, and batch type separation. Another approach of mixed matrix membrane (MMM), which uses composite preparation of pre-synthesized porous material like MOF, COF, HOF and mixed with polymer solution and membrane is casted out of it. One such family of porous polymers (Polymer with intrinsic microporosity (PIM)), works with the principle of microporosity and interconnected pores, as a result of the conformationally rigid, non-planar monomer selection that occupy high van der Waals volume. Fabrication of PIM membrane-using solution processable showed enhanced mass transport and redefine permeability-selectivity trade-off. Structural relaxation in the segmental motion of the linear polymer chains in PIM membrane resulted into reduction of mass transport with time, limited utility for large scale application for separation. The current proposal focuses on increasing mass transfer by enhancing microporosity and reducing the thickness of the polymer membrane. The choice of monomers with the correct balance of van der Waals volume (Vw) and electronic environment is critical to accomplish this goal. From our present understanding we can define some empirical criteria. Rigid, non-planner, contorted and shape-persistent monomers that occupy high van der Waals volume (Vw) are preferred. As a function of selecting monomers with shape persistent and high van der Waals volume, we intent to restrict conformational mobility in the chain packing, allowed a structure to occupy more steric space. This enables in enhancing microporsity and interconnecting porosity. Kinetics of polymerization is mainly governed by thermal gradient and diffusivity of monomers, should be optimized to keep thickness of polymeric membrane as low as possible. |