In 59.68 g of methanol were dissolved 18.88 g (70.12 mmol) of 11-methacrylamidoundecanoic acid (MAU), 1.12 g (7.79 mmol) of 2-(N,N-dimethylamino)ethyl acrylate (Tokyo Chemical industry Co.), and 0.32 g (1.95 mmol) of azobisisobutyronitrile (Nacalai Tesque, Inc.). The solution was deaerated by bubbling nitrogen for 60 minutes. The container was covered with a septum, and the polymerization was conducted by heating at 60° C. for 20 hours. After the completion of the polymerization reaction, the solution was concentrated to dryness under reduced pressure, and the solid was dissolved in 60 g of dimethylformamide. The obtained solution was dropwise added into a large excess of diethyl ether, and the resulting precipitate was collected by filtration under suction. After drying under reduced pressure, 5.22 g of random MAU/2-(N,N-dimethylamino)ethyl acrylate copolymer (90/10) was obtained (yield: 26.1%). The weight average molecular weight was 130000.
