Four types of flexible polyester are synthesized between urethane polyol of polycarbonatediol (PCDL)-isocyanate and carboxylic-terminated polyester pre-polymer. Urethane polyol of PCDL-isocyanate is synthesized between isocyanates such as IPDI and H12MDI and PCDL which has long alkyl chain. Carboxylic-terminated polyester pre-polymers are synthesized using 1,4-CHDA, Ph-An, NPG, 1,6-HD, and 1,4-CHD. The synthesized flexible polyester is measured using GPC and H-1 NMR. From the H-1 NMR spectra, urethane polyol of PCDL-isocyanate has been introduced to the polymer chain of synthesized resin. Those resins are formulated and characterized using DMA and tensile strength, and to control formability and anti-corrosion property. Results showed that storage modulus decreased, and the glass transition temperature shifted to a lower temperature with increasing contents of the urethane polyol of PCDL-isocyanate. So, it provides lower stiffness and higher flexibility to the polyester coatings. CU-IPDI-2 had higher elongation, good formability, and a good anti-corrosion property; thus, it could be used as a primer for automotive coatings.