PH and Salt Effects on Surface Activity and Self-Assembly of Copolymers Containing a Weak Polybase
Copolymers with well-defined architectures, controlled molecular weights, and narrow molar mass dispersities (A) were synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization. The resultant polymers contain different combinations of the pH-responsive monomer 2-(diethylaminoethyl) methacrylate (DEAEMA), the hydrophobic comonomer butyl methacrylate (BMA), and a neutral hydrophilic stabilizing monomer polyethylene glycol monomethyl ether methacrylate (designated O950). Surface tension and cryo-TEM measurements of native and heavy-atom stained samples were used to characterize the pH and salt responsiveness of the different polymers as a function of their composition. These studies indicate that while the polymers predominately self-assemble to form spherical micelles, a narrow size distribution is observed in aqueous solutions of poly(O950)-b-(BMA) and poly(O950)-b-(DEAEMA-co-BMA), whereas a broad size distribution characterizes the assemblies of poly(O950)-b-(DEAEMA) and poly(DEAEMA-co-BMA). In the latter case, micelles having diameters around 15-25 nm are found along with smaller aggregates (about 10 nm) mostly arranged in elongated necklace-like structures. The pH and salt-responsiveness of the DEAEMA residue, as indicated by the surface activity of the copolymers, was found to depend on the nature of the additional components: covalently linked hydrophobic groups (BMA) moderated the pH response of the copolymer as compared to nonionic and hydrophilic groups as in poly(O950)-b-(DEAEMA). These results suggest that mutual interactions among the building blocks of self-assembling copolymers should be taken into account when designing responsive copolymers.
N. Cohen et al., "PH and Salt Effects on Surface Activity and Self-Assembly of Copolymers Containing a Weak Polybase," Langmuir, vol. 32, no. 36, pp. 9286-9292, American Chemical Society (ACS), Sep 2016.
The definitive version is available at https://doi.org/10.1021/acs.langmuir.6b02452
Materials Science and Engineering
Keywords and Phrases
Free radical polymerization; Hydrophilicity; Hydrophobicity; Micelles; Monomers; Size distribution; Solutions, Broad size distribution; Butyl methacrylates; Controlled molecular weight; Hydrophilic groups; Narrow size distributions; Polyethylene glycol monomethyl ether; Reversible addition-fragmentation chain transfer polymerization; Spherical micelles, Self assembly
International Standard Serial Number (ISSN)
Article - Journal
© 2016 American Chemical Society (ACS), All rights reserved.
01 Sep 2016