Abstract The block copolymer poly(2,6-dimethyl-1,4-phenylene ether)- b-polydimethylsiloxane (PPE- b-PDMS) was prepared via hydrosilylation between poly(2,6-dimethyl-1,4-phenylene ether) (PPE) and polydimethylsiloxane (PDMS) homopolymers. The formation of block copolymer was confirmed by 1H NMR and DSC analyses. The block copolymer films were treated by supercritical carbon dioxide (scCO 2) at moderate temperatures under high pressure of 25 MPa for 2 h followed by depressurization. The resulting films showed the microcellular structure by the formation of dense isolated pores, whereas few pores were observed in PPE homopolymer film after the same foaming process. The size of the pores was able to be controlled by varying the processing temperature or the depressurization rate.