Langmuir, Vol.33, No.10, 2628-2638, 2017
Alternative Route to Nanoscale Aggregates with a pH-Responsive Random Copolymer
A random copolymer, poly(methyl methacrylateco-2-dimethylaminoethyl methacrylate) (poly(MMA-co-DMAEMA)) is shown to form nanoscale aggregates (NAs) nm) (similar to 20nm) at copolymer concentrations >= 10% w/w, directly from the preformed surfactant-stabilized latex (similar to 120 nm) in aqueous solution. The copolymer is prepared by conventional emulsion polymerization. Introducing a small mole fraction of DMAEMA (similar to 10%) allows the copolymer hydrophilicity to be adjusted by the pH and external temperature, generating NAs with tuneable sizes and a defined weight-average aggregation number, as observed by dynamic light scattering (DLS) and small-angle neutron scattering (SANS). These NAs are different from the socalled mesoglobular systems and are insensitive to temperature at fixed pH. The relatively broad chemical composition distribution of the copolymer and lumpy (or blocky but not diblock) incorporation of DMAEMA mean that the NAs cannot be simply thought of as conventional polymer micelles. In the acidic pH regime, the amphiphilic copolymer exhibits a defined critical assembly concentration (CAC) and a minimum air-water surface tension of 45.2 mN m(-1). This copolymer represents a convenient route to self-assembled NAs, which form directly in aqueous dispersions after pH and temperature triggers, rather than the typically applied (and time-consuming) water-induced micellization approach for common polymer micelles.