Isolation and analysis of a grafted polymer onto a straight cylindrical pore in a thermal-responsive gating membrane and elucidation of its permeation behavior

We have attained the thermal-responsive gating membrane with a drastic permeability change by several hundredfold; N-isopropylacrylamide (NIPAM) polymers were grafted on the pore surface by the plasma-induced graft polymerization. In this study, we fabricated the gating membrane using a polycarbonate (PC) substrate with straight cylindrical pores. This substrate can be degraded in a strong-alkaline solution, thus the grafted NIPAM polymer was isolated from the substrate and evaluated. Accordingly, we found the grafted polymer has a high molecular weight (from several hundred thousand to a few million) and the polymer chain density is low at ca. 0.01 chains nm−2. These results indicate factors significant to drastic pore gating; the pores are fully open in a shrunken state at the low chain density, by the existence of enough space for shrinking grafted polymers. Further, the pores are sufficiently closed by swollen NIPAM polymers with a small number of high molecular weight polymers. From the above, we clarified the relationship between the property of the grafted polymer and the permeation behavior of the thermal-responsive gating membrane for the first time. Moreover, the knowledge obtained in this study can provide useful guideline for clarifying the gating function obtained by other grafting technique.