Configuration of grafted polystyrene chains in the melt: Temperature and concentration dependence

The concentration profiles of carboxy-terminated polystyrene chains in the melt grafted onto oxide-covered silicon substrates were measured using secondary-ion mass spectroscopy. The grafting density increased with temperature and an enthalpy of +7.4 kcal/mole was deduced for the grafting reaction, SiOH+R(COOH)⇄R(COOSi)+${\mathrm{H}}_2$O. Relatively high grafting densities (σ∼6.6 mg/${\mathrm{m}}^2$) were achieved with minimal chain distortion or displacement of long chains by shorter ones. Significant stretching of the grafted chains occurred for σ>10 mg/${\mathrm{m}}^2$. An equilibrium constant for the grafting reaction incorporating entropy is discussed.