An nanostructured thermoset blend of unsaturated polyester(UPR) and PEO-PPO-PEO triblock copolymer was prepared and characterized by solid-state NMR and other techniques.It is concluded that the blend is microphase separated and the determined long period is 20 nm.A distinct dynamic difference between the cured-UPR matrix and block copolymers was observed by 1D and 2D NMR experiments,the formation of PEO crystalline domains was inhibited in the blend.The PEO blocks are partially miscible with the cured-UPR matrix.Upon curing, part of the mobile PEO was locally expelled from the cured-UPR matrix and formed dispersed microphase together with the mobile PPO,the residual immobilized PEO blocks were intimately mixed with the partially cured-UPR, and they formed an interphase region.