A hyperbranched azo polyurethane was synthesized by an A2type monomer MDI and a B3 type monomer-4-(N

N′-bis(2-hydroxyethyl))amino-2′-hydroxyethoxyl-4′-nitrylazobenzene.The azo polymer was characterized by1H-NMR

UV-Vis spectrum and thermal analysis. The λmax of the polymer in DMF solution was determined to be 488 nm.The number average molecular weight determined by GPC is Mn =9300 with a polydispersion index 1.9.The glass transition temperature (Tg) of the polymer is 131℃ determined from DSC thermogram.The results showed the azo polyurethane has been successfully synthesized through this scheme.Surface-relief-gratings (SRGs) were observed on the polymer film after irradiated by an interference pattern of Ar+ laser beam for 1000 s.The surface modulation depth and the grating spacing were measured by AMF to be 67 nm and 770 nm

respectively.