Hyperbranched azo polyurethane synthesized through A + B scheme

Abstract

A hyperbranched azo polyurethane was synthesized by one-step polymerization of an A₂ type monomer diphenylmethane-4,4′-diisocyanate and a B₃ type monomer 4-(N,N′-bis(2-hydroxyethyl))amino-2′-hydroxyethoxyl-4′-nitro-azobenzene. The azo polymer was characterized by ¹H nuclear magnetic resonance (NMR), ultraviolet-visible (UV-Vis) spectrum and thermal analysis. The ?_max of the polymer in dimethylformamide (DMF) solution is 488 nm. The number average molecular weight (M_n) determined by GPC is 9,300 with a polydispersion index 1.9. The glass transition temperature (T_g) of the polymer is 131°C observed from DSC thermogram. The results show that the azo polyurethane has been successfully synthesized through this scheme. Surface-relief-gratings (SRGs) were fabricated on the polymer film after being irradiated by interference pattern of Ar⁺ laser beams for 1,000 s. The surface modulation depth and the grating space period measured by AMF are 67 and 770 nm, respectively.

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