Abstract:The molecular structure of second generation hydroxyl terminated aliphatic hyperbranched polyester (HB-20) was characterized by Nuclear Magnetic Resonance (NMR) analysis, including One-dimensional (1D) NMR technique (1H NMR, 13C NMR and Distortionless Enhancement by Polarization Transfer (DEPT) NMR spectrums) and two-dimensional (2D) NMR technique (Heteronuclear Single Quantum Coherence (HSQC) NMR and Heteronuclear Multipe Bond Coherence (HMBC) NMR spectrums). Firstly, the chemical shift peaks of the 1H NMR and 13C NMR spectrums were initially assigned, and the four types of carbon atoms (CH3, CH2, CH, and quaternary carbon atom C*) in the HB-20 was distinguished by DEPT NMR spectrum. Secondly, the detailed molecular structure information was further obtained by 2D NMR analysis. From the HSQC spectrum, the 13C-1H COSY spectrum contained all the direct-linked 13C-1H coupling relationships, and the positions of the related 1H and 13C in the molecular structure were determined; from the HMBC spectrum, the 13C and 1H coupling information separated by 2 to 3 chemical bonds was obtained, and the C-C correlation was confirmed to determine the molecular skeleton information of HB-20. According to above NMR analysis, the three relative peak areas of the determined T-CH3, L-CH3, and D-CH3 structures in the 1H NMR spectrum were 2.55, 3.97, and 1.00 respectively, the average degree of branching (DB) of HB-20 was calculated as 0.47. Also the average molecular weight of HB-20 was calculated as 1876 g?mol-1 by NMR analysis, which was closed to the 1878 g?mol-1 obtained from the hydroxyl value titration. In summary, the molecular structure of HB-20 was clearly characterized.