NEUTRON REFLECTIVITY OF END-GRAFTED POLYMERS IN POOR SOLVENT - KINETIC EFFECTS

Kinetics of adsorption of polymers on a solid surface in poor solvent and the competition between long and short chains were studied using n eutron reflectivity. A brush which consists of a 375 K deuterated poly styrene terminated by a zwitterionic end group was grafted on a single crystal silicon wafer from a protonated cyclohexane solution. We foun d that the long deuterated polymer forms a density profile qualitative ly similar to a 50 K protonated polymer studied previously. As for the low molecular weight polymer, the profile consists of a denser layer at the solid surface, a step-like profile convoluted with a Gaussian r oughness and an exponential tail which stretches out almost to the len gth of the same molecular weight in good solvent. Our results also sug gest that the brush, formed in poor solvent, grows in islands and even tually covers the entire surface. After equilibrium was reached, the b rush formed by the 375 K polymer, was exposed to a low molecular weigh t, 26 K protonated polymer. The profile of the long deuterated layer w as studied as a function of time. In poor solvent, a new equilibrium i s formed between the long and the short polymers where the exact compo sition of the long and short chains depends on the temperature and the ratio of the molecular weights.