GRAFTING POLY(ETHYLENE GLYCOL) EPOXIDE TO AMINO-DERIVATIZED QUARTZ - EFFECT OF TEMPERATURE AND PH ON GRAFTING DENSITY

Microparticle capillary electrophoresis was used to characterize the s urface of quartz capillaries grafted with the glycidyl ether of poly(e thylene glycol) (E-PEG). Site dissociation modeling of capillary elect rokinetic behavior provided estimates of surface group pK and density, plus the distance (d) from the surface to the hydrodynamic plane of s hear. Native quartz appeared to possess silanol groups of pK 3.6 and 6 .9 whose surface densities varied with quartz treatment. Aminopropylsi lane derivatization of quartz silanol groups in toluene yielded a coat ing which was stable (>6 h) at pH 10.3 and 60 degrees C. Aqueous graft ing of E-PEG to this surface was relatively independent of pH (7.3-10. 3) and reaction time (6-24 h) but was significantly influenced by reac tion temperature (25-95 degrees C) and salt composition. PEG-grafted c apillaries exhibited greatly reduced electroosmosis from pH 2 to 11. S ignificant grafting could be obtained under mild conditions (6 h, 35 d egrees C, 0.4 M K2SO4, pH 6.9). These results suggest that PEG chains increasingly extend normal to a surface as their grafting density incr eases, and that PEG conformation influences grafting density. The meth ods described should aid the use of PEG-coated surfaces in a variety o f applications.