In order to obtain homogeneous

smooth and size controllable layers of thermosensitive polymer on superfine silica particles

a novel synthetic route was developed.The thermosentive polymer

poly(N-isopro-pylacrylamide)(PNIPAM)

has successfully been grafted onto the surface of superfine silica particles.The synthetic procedure includes the connection of silane coupling agent γ-glycidylpropyltrimethoxysilane (KH-560) with the superfine silica particles

reaction of diethanolamine with glycidyl group of KH-560

and reaction of 2-bromoisobutyryl bromide with resulting hydroxy groups respectively

and finally the ATRP reaction of N-isopropylacrylamide grafting on the superfine silica particle surface.The ATRP was carried out at room temperature in the present of CuCl as a catalyst

ME6TREN as a Ligand

and (50∶50

V/V) DMF/H2O as a reaction medium.The resultant composite particles afforded a coreshell structure.The composites particles were characterized by FTIR

TG

EA

SEM

DSC.The weight losses in TG analysis showed that γ-glycidylpropyltrimethoxysilane

diethanolamine

2-bromoisobutyryl bromide and PNIPAM attached to the silica particles step by step according to the designed route.The grafting ratio of PNIPAM on the surface of silica particles reached to 25.2％ based on the superfine silica.The diagram of DSC indicated the composite silica particle was thermosensitive with LCST of 34.1℃.The GPC measurements for the PNIPAM cleaved from the composite silica particles gave an average molecular weight of 8000

and the molecular weight distribution of 1.06.The SEM images revealed that the modified composite particles had smooth surface

displaying the superiority of active polymerization of ATRP.The results showed that the grafting ratio in this method was higher than that of other methods

the thermosentive polymer on the surface of superfine silica particles formed a homogeneous

smooth and flat layer film

and the modified superfine silica particles will potentially have applications in HPLC.