The effective escape of nanocarriers from endosomal compartments of the cell remains a major hurdle in nanomedicine. The endosomal escape of pH-responsive, self-assembled, dual component particles based on poly[2-(diethylamino)ethyl methacrylate)(PDEAEMA) and poly(ethylene glycol)-b-poly[2-(diethylamino)ethyl methacrylate) (PEG-b-PDEAEMA) has been recently reported. Herein, we report that polymer molecular weight (M ) can be used to tune endosomal escape of nanoparticle delivery systems. PDEAEMA of M 7 kDa, 27 kDa, 56 kDa and 106 kDa was synthesized via reversible addition-fragmentation chain transfer (RAFT) polymerization and co-assembled with PEG-b-PDEAEMA (16 kDa) via nanoprecipitation. All particles had similar size, displayed pH-responsive behaviour, and low toxicity regardless of molecular weight. Ovalbumin was loaded in the particles to demonstrate loading and release capabilities and as a marker to study internalization and endosomal escape. Association and endosomal escape was found to depend on molecular weight, with enhanced escape observed for high M PDEAEMA: 42% of cells with particle induced endosomal escape for 106 kDa nanoparticles, compared to minimal escape for 7 kDa particles. The results show that a simple variation in molecular weight can enhance the endosomal escape of polymeric carriers, and thus improve their effectiveness for intracellular delivery of therapeutics.