Protein-polymer conjugates are widely used in biotechnology and medicine, and non-toxic polymers for bioconjugation would be advantageous for these applications. Herein, we reported the toxicity of polymers synthesized by two commonly employed controlled radical polymerizations: reversible addition-fragmentation chain transfer (RAFT) poly-merization and atom transfer radical polymerization (ATRP). Poly(polyethylene glycolacrylate) (poly(PEGA)) synthesized by RAFT polymerization using a trithiocarbonate chain transfer agent (CTA) was found to provide superior cell viability compared with corresponding polymers prepared by ATRP or RAFT, and therefore was selected as a promising polymer for bioconjugation. Poly (PEGA) was synthesized with different molecular weights and functionalized at the chain end with maleimide, which is known to bea specific reactive group with free thiols on the protein surface. We also attempted to synthesize bis-functionalized maleimide-poly(PEGA) to mimick dimeric structures of proteins frequently found in nature. Polymers were characterized by 1H NMR spectroscopy and size exclusion chromatography (SEC). The kinetics of the RAFT polymerizations were investigated and a linear evolution of molecular weight with monomer conversion was observed. The SEC (IR) analyses showed no detectable side reactions during thepolymerization. However, for the bis-functionalized maleimide-poly (PEGA), a loss of the maleimide end groups was observed during the deprotection procedure. Two modelproteins, V131C T4 lysozyme (T4L) and VEGF165, were expressed, purified, and subsequently conjugated to maleimide-poly (PEGA)s. The resultant conjugates were monitored and purified by SEC (UV), and further analyses were carried out by gel electrophoresis. Lytic activities of T4L conjugates and T4L were monitored by UV-Vis, and bioactivity was not observed