Recently site-specific and stoichiometric modification of proteins with synthetic polymers has attracted a great deal of attentions in numerous fields

such as material science

nanotechnology

biomedicine

diagnostics

and so on.In this work we describe the growth of a brush-like polymer from the N-terminus of proteins via the atom transfer radical polymerization (ATRP) of oligo(ethylene glycol) methacrylate (OEGMA) under mild conditions.Bovine serum albumin (BSA) was used as model protein.The N-terminus of BSA was firstly modified with pyridoxal-5-phosphate (PLP).Then reacted with a hydroxylamine-functionalized ATRP initiator (i.e.

(2-(aminooxy)ethyl) 2-bromo-2-methylpropanoate

ABM)

formed the so called macroinitiator (i.e.

BSA-Br).After that

ATRP was successfully carried out on the BSA-Br macroinitiator using OEGMA as monomers

giving rise to a BSA-POEGMA conjugate.The resulting compounds were characterized using Fourier transform infrared spectroscopy (FTIR)

nuclear magnetic resonance (NMR)

ultraviolet-visible spectroscopy (UV-Vis) and matrix-assisted laser desorption/ionization time of flight mass spectrometry (MALDI-TOF-MS).The FTIR and 1HNMR results clearly indicated the successful synthesis of ABM.The UV-Vis spectrum of BSA-Br showed a new absorption peak at λ=328 nm compared to that of pure BSA

which suggested the coupling between BSA and ABM.MALDI-TOF-MS data showed that two ABM molecules were coupled with BSA.The synthesis of the stoichiometric (1:2) BSA-POEGMA conjugate was also confirmed by means of FTIR

UV-Vis and MALDI-TOF-MS measurements.The degree of polymerization (DP) for POEGMA segment was calculated to be 105

which was close to theoretical value (i.e.

DP=100).