Siloxane-functionalized poly(ether carbonate)s (Si-PECs) were synthesized from terpolymerization of carbon dioxide (CO2), propylene oxide (PO), and [3-(2,3-epoxypropoxy)propyl]-trimethoxysilane (KH-560). Si-PECs with different molecular weights (1500-4000 Da) and siloxane content (0-9.8% by mole) were obtained and used as the soft segments of waterborne polyurethane (WPU). The carbonate unit in polyols improved the mechanical and oxidation resistance of WPU, whereas the siloxane units offered higher cross-linking density and thermal stability. The particle size of the Si-PEC-WPU emulsion varied from 100 to 684 nm as the siloxane unit content in Si-PEC increased. Further, the Si-PEC-WPU film prepared from Si-PEC having an M-n of 2200 and a siloxane content of 3.9% by mole showed not only excellent mechanical performance with a tensile strength of 16.5 MPa and elongation at a break of 683.4% but also good hydrophobicity because of the carbonate units and siloxane units. To summarize, Si-PECs derived from CO2 and inexpensive silane coupling agents show good promise as an alternative for commodity polyols for WPU applications.