This study describes the synthesis and aggregation behavior of thermosensitive poly(di(ethylene glycol) monomethyl ether methacrylate) (P(DEGMA-ME)) conjugated with the fluorescently labeled pentapeptide glycine-arginine-lysine-phenylalanine-glycine-dansyl (GRKFG-Dns). The GRKFG-Dns was obtained using Fmoc solid-phase peptide synthesis and was modified with 2-bromopropionic acid to initiate an atom transfer radical polymerization of di(ethylene glycol) monomethyl ether methacrylate (DEGMA-ME). The polymerization led to a well-defined P(DEGMA-ME)GRKFG-Dns conjugate with a number average molar mass of 108,000 g/mol. The pentapeptide acted as a hydrophilic moiety that increased the phase transition temperature compared to the P(DEGMA-ME) homopolymer of similar molar mass. The bioconjugate macromolecules aggregated in dilute aqueous solution into spherical particles (mesoglobules). The sizes of aggregates were easily controlled by changing the concentration and heating rate of the P(DEGMA-ME)-GRKFG-Dns solution. The weight average molar masses and sizes of mesoglobules were determined based on light scattering measurements. Enzymatic hydrolysis of the bioconjugate in dilute solution was performed at temperatures below and above the cloud point temperature of the bioconjugate. The peptides were fully accessible to enzymatic digestion even when the macromolecules were aggregated to mesoglobules, indicating that the peptide segments in mesoglobules formed the external shell of the nanoparticles and could be easily released by enzymes. (c) 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012