Synthesis of soluble oligsiloxane-end-capped hyperbranched polyazomethine and their application to CO2/N2 separation membranes

Three soluble hyperbranched polyazomethines containing oligosiloxane end group HBP-PAZ-SiOn were successfully synthesized. HBP-PAZ-SiOns were used as modifiers of ethyl cellulose (EC) and polysulfone (PS) membranes. Blend membranes, HBP-PAZ-SiOn/EC and HBP-PAZ-SiOn/PS were prepared by blending the THF solution of HBP-PAZ-SiOn with ethanol solution of EC and dichloromethane solution of PS, respectively. Surprisingly, the permeabilities for CO2 of the blend membranes were more than 15–16 times higher than those of pure EC and PS membranes without any drop of pemselectivity to N2. This unusual improvement has been achieved by both enhancement of diffusivity for carbon dioxide and nitrogen by the oligosiloxane groups and enhancement of affinity of the amino groups with carbon dioxide at the end groups of HBP-PAZ-SiOn.