An acrylate is polymerized by the photodecomposition of to make a polymeric intermediate containing dithiocarbamate groups at both its ends, and a hard polymer-forming monomer is polymerized by the photodecomposition of this dithiocarbamate group-containing polymeric intermediate to form blocks of a polymer of said hard polymer-forming monomer on both sides of said polymeric intermediate, thereby forming an ABA type block copolymer.
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