Kinetically Driven Intra- and Interchain Association of Hydrophobically and Hydrophilically Modified Poly(acrylic acid) in Dilute Aqueous Solutions

Effects of pH, dodecyl, and PEO contents as well as the method of preparing the solution on the formation of the unimolecular micelles (unimer micelle) or aggregates made of poly(acrylic acid)- graft -poly(ethylene oxide)- graft -dodecyl (PAA- g -PEO- g -dodecyl) and PAA- g -dodecyl have been studied by a combination of static and dynamic laser light scattering (SLS and DLS). It revealed that: in most cases, these copolymers tend to form interchain associates; while low pH value, proper high dodecyl content and fast switch rate of solvent quality promote intrachain association. These phenomena of the system being trapped in a metastable state can be mainly attributed to its kinetic pathway: the factors mentioned earlier can enhance the initial intrachain contraction, leading to τ c (interaction time) ≪ τ e (entanglement time) for the two interaction intrachain globules. So they behave like tiny “elastic balls” and their further merge/fusion become nearly impossible during their interaction time (τ c ). In this way, the copolymer system is trapped in the metastable, unimer micelle state. The interplay of τ c and τ e in the formation of metastable unimer micelles or stable aggregates has been discussed in detail.