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

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 (Γmax), the minimum area (Amin) and the adsorption standard free energy ΔGads°, were evaluated using the average monomeric molecular weight (MnA). The results showed that Γmax decreased with the increase in pH and the corresponding Amin enlarged with the increase in pH. But Γmax increased with the increase in temperature, as the corresponding Amin shrank with the increase in temperature. The variations of ΔGads° 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 ΔGmic° 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.

The conformation of SMA-M aggregates in aqueous solution transformed from connected micelle-like aggregates via “necklace” to isolated swollen micelle-like aggregates then to rod-like aggregates with the increase in pH at room temperature.Figure optionsDownload as PowerPoint slideHighlights
► The pH-effective and thermo-effective aggregation behavior of amphiphilic comb-like copolymer SMA-M was investigated.
► The Γmax, Amin, ΔGads° and ΔGmic° were evaluated using the average monomeric molecular weight MnA.
► The expansion degree of backbone varied with pH was the dominative factor influenced the aggregation behavior.
► The transformation of aggregate structure of SMA-M with the increase in pH was deduced.