Polymers made from zwitterionic repeat units (bearing no net charge) have intriguing solution properties, especially in contrast to polyelectrolytes, such as an apparent indifference to salt concentration. These polyzwitterions (PZs) have come under renewed scrutiny because of their use in high performance antifouling coatings. Here, an amidosulfobetaine polymer was used to shed light on the complex and poorly understood response of PZ solution conformation to ionic strength. A Hofmeister anion series NaX, where X = SO4 2–, Cl–, Br–, NO3 –, ClO4 –, and SCN–, provided a systematic way to tune PZ/ion interactions. A consistent picture of PZ conformation emerged, where the role and location of counterions (how they pair with the polymer chain) depend on their position in the Hofmeister series. At least four regimes of PZ conformation/interaction as a function of ionic strength were observed, the last showing no change in coil size (hydrodynamic radius) as a function of ionic strength for all monovalent salts in the concentration range 0.6–4 M. Hydrophobic (less hydrated) anions ClO4 – and SCN– yielded a clear minimum in coil size at lower [NaX], whereas PZ in solutions of hydrophilic ions SO4 2– and Cl– showed only a hint of the much-discussed “anti-polyelectrolyte” expansion of PZ with increasing [NaX]. Static light scattering results, when analyzed using Stockmeyer’s theory of scattering from multicomponent systems, revealed that NaX is associated with PZ with a corresponding increase in apparent molecular weight. Static light scattering measurements at low [NaX] show solution ions are excluded from PZ coils dressed with hydrophobic NaX. Dynamic light scattering in salt-free solutions at elevated temperatures revealed substantial chain stiffening of PZ, thought to be caused by nearest-neighbor interactions between zwitterion groups. DLS yielded a fast mode in these salt-free solutions, ascribed to soliton-like transport of waves of associated zwitterionic groups along the PZ backbone.
The coil size of narrow molecular weight distribution deuterated poly(styrenesulfonate), PSS, within a polyelectrolyte complex doped with KBr was tracked across the continuum from solid to coacervate to solution using small-angle neutron scattering. While PSS alone in solution exhibited the familiar and pronounced "polyelectrolyte effect" of coil shrinkage with increasing [KBr], the radius of gyration R g of the PSS in the complex remained surprisingly constant up to 1.4 M KBr, which is close to the transition between complex and coacervate behavior. Thereafter, R g decreased with increasing KBr, remaining slightly larger than R g for PSS in KBr alone. Upturns in the scattering at low angle, seen for complexes in lower [KBr], are consistent with porosity, observed macroscopically as whitening of the bulk complexa universal property of polyelectrolyte complexes. Reasons for this porosity, imaged by scanning electron microscopy, are discussed. At high q ranges, a correlation peak between deuterated coils of PSS was observed.
A precision polyethylene containing phenyl branches at every fifth carbon (p5Ph) is nearly quantitatively functionalized (≈95%) with sulfonic acid groups on the para-position of each phenyl branch (p5PhS-H). Unlike polystyrene sulfonate (PSS), p5PhS-H has a glass transition temperature (T = 109 °C) well below its thermal decomposition temperature (T ≈ 200 °C), making this new material capable of thermal processing into molds and films at temperatures between these thermal limits. Neutralization of the sulfonic acid groups with varying counter cations (Li , Na , Cs ) produces a new class of precision polyelectrolytes. Neutralization and increasing size of the counter cation improves the thermal decomposition temperature (T ) to over 400 °C for the Cs form. Neutralization causes T to increase above T for the Li and Na form. The Cs form is found to have an accessible T = 294 °C. Further investigations of water absorption and the polyelectrolyte effect of these systems are discussed.
The release of counterions drives the efficient blending of oppositely charged polyelectrolytes when they complex. In theory, mixing like-charged macromolecules before complexation should offer a significant scope for controlling the composition and properties of polyelectrolyte complexes/coacervates. In practice, not much is known about the relative affinities between charged components and how they might compete for limited supplies of oppositely charged partners. In this work, we contrast the use of mixtures of poly(styrene sulfonate), PSS, and poly(methacrylic) acid, both polyanions, with copolymers of the same repeat units competing for poly(diallyldimethylammonium), PDADMA, a polycation. Using the layer-by-layer, or multilayering, technique ensures that the polycation is always a limiting reagent. Although the composition of the thin film of a polyelectrolyte complex faithfully mirrored the solution copolymer composition, strong deviations from solution composition were observed with blends of homopolymers. There is a degree of thermodynamic control over film composition, related to the difference in free energy of formation of PDADMA/PSS versus PDADMA/poly(methacrylic acid) repeat unit pairs.
Interfaces bearing firmly attached thiol groups are useful for many applications requiring the versatile and facile chemistry of the −SH functionality. In this work, rugged ultrathin films were prepared on substrates using layer-by-layer assembly. The surface of these smooth films was capped with a co-polymer containing benzyl mercaptan units. The utility of this coating was illustrated by three applications. First, thiol-ene “click” chemistry was used to introduce the Arg-Gly-Asp (RGD) adhesive peptide sequence on a surface that otherwise resisted good adhesion of fibroblasts. This treatment promoted cell adhesion and spreading. Similar Michael addition chemistry was employed to attach poly(ethylene glycol) to the surface, which reduced fouling by (adhesion of) serum albumin. Finally, the affinity of gold for −SH was exploited by depositing a layer of gold nanoparticles on the thiolated surface or by evaporating a tenacious film of gold without using the classical chromium “primer” layer.
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