The synthesis of poly(2-hydroxylthyl methacrylate) grafted soy protein isolates (SPI-g-PHEMA) using atom transfer radical polymerization (ATRP) was described.Poly(2-hydroxyethyl methacrylate) (PHEMA) is one of most extensively studied biocompatible polymer

which has been used for applications such as contact lenses.The scheme of the work was that the soy protein isolate macroinitiator (SPI-Br) was synthesized first by condensation reaction of the active amino groups and 2-bromoisobutyryl bromide

and the resulting secondary bromide could be used as initiator for HEMA monomer in atom transfer radical polymerization to propare SPI-g-PHEMA.FTIR and 13C-NMR spectra confirmed the conversion from SPI sequence to SPI-Br.Atom transfer radical polymerization of 2-hydroxyethyl methacrylate (HEMA) on SPI was carried out in aqueous solutions using SPI-Br as initiator

copper chloride/bipyridine (CuCl/bpy) as catalyst.FTIR spectrum was used to characterize the successful polymerization of HEMA onto SPI globulin.The graft chain was cleaved from SPI-g-PHEMA by degradation of hydrochloric acid for purpose of the measurement of molecular weight of graft chain by GPC.The changes in the spectra of SPI

SPI-Br

SPI-g-PHEMA and grafted chain confirmed successive steps in the synthesis of SPI-g-PHEMA hybrids.A series of comparative experiments were taken with different reaction mediums（H2O

H2O/n propanol

n-propanol）

and higher molecular weight result was gained in aqueous solutions by ATRP.The number average molecular weight was about 1.16×104

and a polydispersity was about 1.12

so the water medium system was chosen for further study.The molecule weight and the polydispersity of graft chain cleaved from SPI-g-PHEMA prepared via ATRP initiated by soy protein isolate macroinitiator were similar to those of PHEMA prepared by normal ATRP using 2-bromoisobutyryl bromide without SPI in solution under similar reaction conditions.The solution properties of SPI-g-PHEMA were characterized by UV and fluorescent spectrophotometer.The results indicated that with increasing of pH value

the solubility of SPI and SPI-g-PHEMA increased

and the hydrophobicity decreased.The zeta-potential of SPI and SPI-g-PHEMA solutions were also studied by zeta-potentiometer.The static charges on the surface of SPI molecules increased clearly after graft modification

and the values of the zeta potential of SPI and SPI-g-PHEMA solutions decreased with the increase of pH values.The TEM images showed that the diameter of SPI-g-PHEMA was beyond that of SPI

and the morphologies of SPI and SPI-g-PHEMA were different.