Materials
All the chemicals used in the production process are commercially available and did not require further refinement.o -phenylenediamine (o -PD), N,N-dimethylformamide (DMF), n-Hexane, dichloromethane (DCM), dibutyltin dilaurate (DBTDL) were purchased from Shanghai Macklin Biochemical Co., Ltd. 2-amino-4-hydroxy-6-methylpyrimidine (UPy) was purchased from Shanghai yuanye Bio-Technology Co.,Ltd. 1, 6-hexad -iisocyanate was purchased from Energy Chemical of Sahn Chemical Technology (Shanghai) Co., LTD. ethylenediamine tetraacetic acid (EDTA) was purchased from Aladdin Industrial Corporation (Shanghai, China) .Ultrapure water from the Millipore system was used in all experiments.