title: pH and Salt Effects on Surface Activity and Self-Assembly of Copolymers Containing a Weak Polybase.
abstract: Copolymers with well-defined architectures, controlled molecular weights, and narrow molar mass dispersities (Đ) 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.
authors.affiliation: Department of Chemical Engineering, The Ben-Gurion University of the Negev , Beersheba 8410501, Israel.
authors.forename: Neta
authors.initials: N
authors.lastname: Cohen
authors.affiliation: Department of Chemical Engineering, The Ben-Gurion University of the Negev , Beersheba 8410501, Israel.
authors.forename: Lana
authors.initials: L
authors.lastname: Binyamin
authors.affiliation: The Center for Nanoscience and Nanotechnology, The Hebrew University of Jerusalem , Jerusalem 91904, Israel.|The Institute for Life Sciences, The Hebrew University of Jerusalem , Jerusalem 91904, Israel.
authors.forename: Yael
authors.initials: Y
authors.lastname: Levi-Kalisman
authors.affiliation: Department of Bioengineering, University of Washington , Seattle, Washington 98105, United States.
authors.forename: Geoffrey Y
authors.initials: GY
authors.lastname: Berguig
authors.affiliation: Department of Bioengineering, University of Washington , Seattle, Washington 98105, United States.
authors.forename: Anthony
authors.initials: A
authors.lastname: Convertine
authors.affiliation: Department of Bioengineering, University of Washington , Seattle, Washington 98105, United States.
authors.forename: Patrick
authors.initials: P
authors.lastname: Stayton
authors.affiliation: Department of Chemical Engineering, The Ben-Gurion University of the Negev , Beersheba 8410501, Israel.|The Ilse Katz Institute for Nanoscale Science and Technology, The Ben-Gurion University of the Negev , Beersheba 8410501, Israel.
authors.forename: Rachel
authors.initials: R
authors.lastname: Yerushalmi Rozen