RAFT Dispersion Alternating Copolymerization of Styrenewith N-Phenylmaleimide: Morphology Controland Application as an Aqueous Foam Stabilizer

摘要

We report a new nonaqueous polymerization-induced self-assembly (PISA) formulation based on the reversible addition–fragmentation chain transfer (RAFT) dispersion alternating copolymerization of styrene with N-phenylmaleimide using a nonionic poly(N,N-dimethylacrylamide) stabilizer in a 50/50 w/w ethanol/methyl ethyl ketone (MEK) mixture. The MEK cosolvent is significantly less toxic than the 1,4-dioxane cosolvent reported previously [Yang P.. ; et al.Macromolecules 2013, 46, 8545−8556 []]. The core-forming alternating copolymer block has a relatively high glass transition temperature (Tg), which leads to vesicular morphologies being observed during PISA, as well as the more typical sphere and worm phases. Each of these copolymer morphologies has been characterized by transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS) studies. TEM studies reveal micrometer-sized elliptical particles with internal structure, with SAXS analysis suggesting an oligolamellar vesicle morphology. This structure differs from that previously reported for a closely related PISA formulation utilizing a poly(methacrylic acid) stabilizer block for which unilamellar platelet-like particlesare observed by TEM and SAXS. This suggests that interlamellar interactionsare governed by the nature of the steric stabilizer layer. Moreover,using the MEK cosolvent also enables access to a unilamellar vesicularmorphology, despite the high Tg of thealternating copolymer core-forming block. This was achieved by simplyconducting the PISA synthesis at a higher temperature for a longerreaction time (80 °C for 24 h). Presumably, MEK solvates thecore-forming block more than the previously utilized 1,4-dioxane cosolvent,which leads to greater chain mobility. Finally, preliminary experimentsindicate that the worms are much more efficient stabilizers for aqueousfoams than either the spheres or the oligolamellar elliptical vesicles.