Catheters-associated infections, which are caused by bacteria fouling and subsequent biofilm formation, are difficult to treat. In this study, diblock copolymers of antifouling poly(ethylene glycol) (PEG) having different lengths (2.4 kDa and 10 kDa) and maleimide-functionalized polycarbonate (2.4k-M and 10k-M), and diblock copolymers of PEG and polycarbonate functionalized with maleimide and ammonium (2.4k-MC and 10k-MC) were synthesized by metal-free organocatalytic ring-opening polymerization. These polymers were employed to coat onto thiol-functionalized silicone rubber (a commonly used catheter material) surface to investigate the effects of PEG length and cationic polycarbonate on antibacterial and antifouling activities. Upon contact, the 2.4k-MC and 10k-MC coatings that contain cationic polycarbonate eliminated 96% and 98% of S. aureus, and 93% and 96% of E. coli in solution, respectively, while they were unable to prevent bacteria fouling or biofilm formation. Unexpectedly, although the surface coated with 2.4k-M or 10k-M without antibacterial cationic polycarbonate block did not kill S. aureus and E. coli in solution, these coatings provided stronger antifouling function. Particularly, the 10k-M coating of longer PEG had stronger antifouling activity, and precluded formation of S. aureus and E. coli biofilms over 14 days. Moreover, the coating prevented protein fouling and platelet adhesion without inducing hemolysis. Therefore, this antifouling polymer coating is a potentially viable candidate to prevent catheter-associated infections.