The present invention provides a method for the covalent immobilization of biomolecules on polymers for delivery of the biomolecules, which has the advantage of being simple, highly efficient, environmentally friendly and free of side products relative to traditional immobilization techniques. The invention provides a modified micro/nanoparticle system, which uses a functionalized polymer formed into micro or nanoparticles to bind a molecule to the particles using uses facile chemistry, the Diels-Alder cycloaddition between a diene and a dienophile with the polymer being functionalized with one of them and the molecule with the other, or the Huisgen 1,3-dipolar cycloaddition between a terminal alkyne and an azide to bind the molecule to the particle. The molecules and/or other therapeutic agents may be encapsulated within the polymer particles for intravenous therapeutic delivery. The invention also provides a novel synthetic biodegradable polymer, a furan/alkyne-functionalized poly(trimethylene carbonate) (PTMC)-based polymer, whose composition can be designed to meet the defined physical and chemical property requirements. In one example, the particle system self-aggregates from functionalized PTMC-based copolymers containing poly(ethylene glycol) (PEG) segments. The composition of the copolymers can be designed to meet various particle system requirements, including size, thermodynamic stability, surface PEG density, drug encapsulation capacity and biomolecule immobilization capacity.