disclosed are a block - graft copolymer comprising a polymer block having a repetitive unit represented by general formula : ## str1 ## wherein a represents an organopolysiloxane chain , a polyalkylene oxide chain , a polyalkylene - imine chain , a polyacrylate chain or a polyacryloyl chain , and a process for producing the same . this block - graft copolymer can have various performances such as an oxygen enrichment performance , an ion concentration property , a capability of forming a complex with a metal salt and a biocompatibility , depending on the kind of graft polymer chains .