Polyelectrolyte complexes are a fascinating class of soft materials that can span the full spectrum of mechanical properties from low-viscosity fluids to glassy solids. This spectrum can be accessed by modulating the extent of electrostatic association in these complexes. However, to realize the full potential of polyelectrolyte complexes as functional materials, their molecular level details need to be clearly correlated with their mechanical response. The present work demonstrates that by making simple amendments to the chain architecture, it is possible to affect the salt responsiveness of polyelectrolyte complexes in a systematic manner. This is achieved by quaternizing poly­(4-vinylpyridine) (QVP) with methyl, ethyl, and propyl substituentsthereby increasing the hydrophobicity with increasing side chain lengthand complexing them with a common anionic polyelectrolyte, poly­(styrene­sulfonate). The mechanical behavior of these complexes is compared to the more hydrophilic system of poly­(styrene­sulfonate) and poly­(diallyldimethyl­ammonium) by quantifying the swelling behavior in response to salt stimuli. More hydrophobic complexes are found to be more resistant to doping by salt, yet the mechanical properties of the complex remain contingent on the overall swelling ratio of the complex itself, following near universal swelling–modulus master curves that are quantified in this work. The rheological behaviors of QVP complex coacervates are found to be approximately the same, only requiring higher salt concentrations to overcome strong hydrophobic interactions, demonstrating that hydrophobicity can be used as an important parameter for tuning the stability of polyelectrolyte complexes in general, while still preserving the ability to be processed “saloplastically”.

Polymeric materials as anion exchange membranes (AEMs) play an essential role in the field of energy and environment. The achievement of high performance AEMs by the precise manipulation of macromolecular architecture remains a daunting challenge. Herein, we firstly report a novel rod-coil graft copolymer AEM, possessing rigid hydrophobic main chains and soft hydrophilic graft chains. The low graft density, which can alleviate the adverse influences of ioinc graft chains on the main chains, was obtained by using the living polymerization technique. Consequently, the grafted ionic groups which result in the degradation of polymer backbone was decreased to a small degree. Moreover, the relatively long graft chains induced the nanophase separation between the hydrophobic polymer chains and hydrophilic graft chains, which creates a convinient pathway for high hydroxide ion mobility. Such an accurate molecular design simultaneously improves the hydroxide ion conductivity and alkaline stability as well as dimensional stability.

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Poly(methyl methacrylate)−poly(methacrylic acid)−poly(methyl methacrylate) (PMMA−PMAA−PMMA) triblock copolymers can self-assemble into well-defined elastic hydrogels in water by forming glassy PMMA micelle cores connected with PMAA bridges. The stiffness and toughness of these hydrogels are enhanced substantially by introducing partially quaternized poly(4-vinylpyridine) (QVP) into the system. Interactions between the QVP and PMAA molecules provide an energy dissipation mechanism, with fracture energies in excess of 1000 J/m 2 obtained in some cases. The materials are fully self-assembled and are formed by exposing liquid solutions in DMSO to small amounts of water. The simplicity of gel formation, and the ability to adjust the chemical and physical characteristics of these materials over a wide range, make them excellent model systems for fundamental investigations of the mechanical response of ion-containing gels.

The interactions between polymer molecules in solution are strongly affected by the way that the constituent polymers interact with the solvent. In this work, we use a mixed solvent system (dimethyl sulfoxide and ethylene glycol) to tailor the strength of the hydrogen-bonding interactions between partially quaternized poly­(4-vinylpyridine) [QVP] and poly­(methacrylic acid) [PMAA]. The charge introduced by the quaternization reaction enables homogeneous solutions to be formed over a large concentration range, even in the presence of attractive hydrogen-bonding interactions between the proton-donating PMAA and the proton-accepting QVP. The viscoelastic properties of equimolar QVP/PMAA solutions are superposed onto master curves that are well-described by a fractional Maxwell liquid model. This model provides a means for quantifying the dependence of the relaxation times on the solvent composition. These relaxation times increase by a factor of 1000 as the hydrogen-bonding interactions are strengthened by a decrease in the DMSO content of the solvent, within a composition regime where the solutions remain homogeneous. A much stronger effect is obtained when the ethylene glycol is replaced by water.