Synthesis of UPy-NCO
UPy-NCO was prepared with 2-amino-4-hydroxy-6-methyl -pyrimidine (UPy) and 1, 6-hexadiisocyanate in N2atmosphere. Simply, the solution of UPy (2.3 g) and HMC diisocyanate (35 mL) was added to Schlenk flask. After 10 min of scavenging under N2 atmosphere, the reaction solution was heated to 100 oC. After stirring at 100 oC for 24 h, the reaction mixture was poured into n-Hexane. The resulting sediment was filtered and washed with fresh n-Hexane to remove impurities. Overnight in a vacuum drying oven, white solid powder was obtained. Then the white solid powder was washed three times with fresh chloroform and dried for later use.