ABA type block copolymerization of N-phenylmaleimide (NPM), N-hexyl maleimide (NHM), methyl methacrylate (MMA), and butyl methacrylate (BMA) was investigated by group transfer polymerization (GTP) with [1,5-bis (trimethylsilyloxy)-1,5-dimethoxy-1,4-pentadiene] (1) as difunctional initiator. A novel block copolymers (2) of NPM and MMA (or BMA) could be prepared by sequential addition of NPM to the living PMMA (or PBMA) produced with 1. The reaction did not exhibit the characteristics of living polymerization when NPM was added. The resulting copolymers showed good thermal stability. On the other hand, gelation occurred in GTP of NHM.