A similar synthetic strategy has also been applied to the design of polymer prodrug nanocarriers physically loaded with a second drug, for combination therapy purposes and to overcome drug resistance. This was exemplified by the design of a monomer prodrug of ibuprofen (HEMA-ester-Ibu) by esterification of HEMA by carbodiimide coupling chemistry, followed by its polymerization initiated by PEG-4-formylbenzoic acid (CBA)-Br as an ATRP initiator. The resulting amphiphilic PEG-b-P(HEMA-ester-Ibu) diblock copolymers formed micelles of 214 nm with high drug loading (~47 wt %), and exhibited two levels of pH-sensitivity: