Polymeric membranes are used for many separations. Some act as selective filters, separating viruses and other undesirable solutes from drinking water. Others perform chemical separations, separating air to make an atmosphere which extends fruit shelf-life. The ability of a membrane to perform a separation is determined by its chemistry and microstructure.
Block polymers are macromolecules composed of two or more chemically incompatible polymers (blocks) covalently bonded together. Depending upon the relative amounts of each block, the polymer forms different ordered structures 5-50 nm in scale. This control over the constituent polymers and microstructure will be used to produce membranes with different transport properties. Ammonia selective membranes which retain selectivity in mixed gas systems are made from poly(cycloocetene-b-styrene sulfonate). Using poly(styrene-b-lactide) as a template, ultrafiltration membranes with a monodisperse pore size distribution are formed.