A tri-branched copolymer comprises a hydrophobic domain, a hydrophilic domain, a biologically active moiety, and an alkyl core of 2 to 10 carbon atoms. The hydrophobic domain, the hydrophilic domain, and the biologically active moiety are separately linked to the alkyl core of 2 to 10 carbon atoms through three functional groups, wherein said three functional groups are independently the same or different. Preferably, the tri-branched copolymer is prepared through reversible addition fragmentation transfer (RAFT) polymerization and conjugation reactions. The copolymer can be used as a coating composition for applying on at least a portion of one surface of an article, especially a medical device or a component of a medical device.
