Cationic polymers possess significant potential in various biomedical applications due to their favorable interactions with biocomponents in aqueous media, which is related to their inherent structure and associated water structure. This work presents the development of a novel biodegradable cationic polymer with specific associated water structure and unique interactions with biocomponents. Bioinspired branched dicationically-charged phosphodicholine-chitosan (PdCCs) with different substitute degree were synthesized via Atherton-Todd reaction. As compared with monocationically charged N-(2-hydroxyl) propyl-3-trimethyl ammonium chitosan chloride (HTCC), thermal analysis confirmed the existence of the freezing bound water surrounding PdCCs due to the introduction of branched dicationically-charged PdC moiety. Fluorescence spectra revealed that PdCCs induced much less conformational change of bovine serum albumin than HTCC. Antibacterial and hemolysis assay showed that PdCCs and HTCC displayed high antibacterial activities against Escherichia coli and Staphylococcus aureus with different bacterial-type selectivity, and PdCCs showed higher selectivity to kill bacteria over red blood cell than HTCC. Furthermore, PdCCs-immobilized antibacterial surfaces exhibited better hydrophilicity and less protein adsorption than HTCC-immobilized antibacterial surfaces. These results indicated that branched dicationic PdC with capacity to restrain the freezing bound water may provide a good choice for developing cationic polymers for therapeutic applications.