Aggregation behavior of amphiphic comb-like copolymer containing poly(ethylene oxide) methyl ether grafts

Abstract

The amphiphilic comb-like copolymer, poly(styrene-co-maleic anhydride)-g-(poly(ethylene glycol) monomethyl ether) (SMA-M), was prepared by one-pot method. Its aggregation behavior was investigated by equilibrium surface tension method, rheological technology and transmission electron microscopy (TEM). The equilibrium surface tension of SMA-M solution with various pH at different temperatures was plotted against molar concentration of St-co-MA unit. The adsorption data, such as the saturation surface excess concentration ( Γ max), the minimum area ( A min) and the adsorption standard free energy Δ G ads ° , were evaluated using the average monomeric molecular weight ( M nA). The results showed that Γ max decreased with the increase in pH and the corresponding A min enlarged with the increase in pH. But Γ max increased with the increase in temperature, as the corresponding A min shrank with the increase in temperature. The variations of Δ G ads ° with pH and temperature indicated that the increase in expansion degree of backbone with the increase in pH was the dominative factor influenced the adsorption data. The results of micellization standard free energy Δ G mic ° suggested that the increase in expansion degree of backbone made it difficult to form micelle-like aggregates, even though the increase in temperature leaded to the stronger hydrophobic property. Associated the results from rheological measurement and TEM method, the conclusion was reached that the aggregate structure of as-prepared SMA-M transformed from micelle-like aggregates connected by “necklace” to isolated swollen micelle-like aggregates, then to rod-like aggregates with the increase in pH.