Composite membranes containing molecular sieve particles embedded in a polyimide matrix are promising due to their increased permeability and high selectivity in gas separation processes. Determination of permeability of dense membranes is time-consuming and the resulting values are loaded with experimental errors. The impact of uncertainty in various quantities on the reliability of the permeability values measured by the constant volume/ variable pressure method was analyzed. The total uncertainty of the measurements on polyimide/Silicalite-1 membranes is 7–13 %, the errors in membrane thickness and permeation coefficient being the main contributing factors.
Over the recent decades, hyperbranched polymers have received much attention in both academic and industrial sphere. Due to their highly branched structure and multifunctionality, hyperbranched polymers exhibit unique chemical and physical properties. Many hyperbranched polymers have been prepared by one-step polymerization. The polymerizations can be divided into three categories: step-growth polycondensation of ABx monomers, selfcondensative vinyl polymerization of AB* monomers and branching ring-opening polymerization of hypothetical ABx monomers. This review highlights some examples of synthesis of the most important hyperbranched polymers. Special attention is paid to step-growth polycondensation of ABx-type monomers and to polycondensation of A2 and B3 monomers. Some properties of hyperbranched polymers and their potential applications are also described.
