X-ray scattering data were used to examine the morphological evolution that accompanies the ionomer-to-polyelectrolyte transition. Bulk random ionomer based on methacryl diglyme side chains and sodium sulfonated styrene exhibits an amorphous halo, a backbone correlation peak, and an ionic aggregate spacing peak in X-ray scattering. The ionic peak intensifies as either polymer content or temperature increases due to enhanced aggregation, since the dielectric constant of the polar liquid decreases as temperature is raised. Addition of polar plasticizer into the ionomer softens the ionic interactions by raising the dielectric constant, which weakens the ionic peak, leading to more polyelectrolyte character at higher plasticizer content, with many dissociated Na counterions. There is a wide range of ion content and dielectric constant (gray region in graphic) within which these materials transition from ionomer to polyelectrolyte as the polar plasticizer is added, and both the ionic aggregation peak of the ionomer and the correlation length (interchain spacing) of polyelectrolyte solutions can be resolved. The complete transition to polyelectrolyte occurs when the average distance between the ions becomes larger than the Bjerrum length, so that many Na counterions dissociate, and the ionic aggregate spacing peak disappears.

The linear and nonlinear rheological behaviors of nonentangled sulfonated polystyrene (SPS) ionomers near the sol–gel transition were studied. When the degree of sulfonation, p, was below the gel point, the ionomer exhibited sol-like linear viscoelastic (LVE) behavior, and shear thinning was observed for steady shear flow. For p close to the gel point, the ionomer showed power-law-like LVE behavior over a wide frequency range. Strain hardening and shear thickening behavior were observed, and their magnitudes depended on the temperature, molecular weight of the PS precursor, and the Coulomb energy of the ion pair. Above the gel point, a distinct rubbery plateau was observed in the dynamic modulus. Melt fracture occurred upon start-up shear, which prevented quantitative examination of the nonlinear rheology. The possible mechanisms for strain hardening and shear thickening near the gel point are discussed with respect to formation of large clusters that nearly percolate in space.

Linear viscoelastic and dielectric measurements were conducted for a model associating polymer system, n-butyl acrylate (PnBA)-based copolymers containing 2-ureido-4[1H]-pyrimidinone (UPy) groups as stickers. The number of stickers per chain was varied from less than one to more than two, which covered a sol-to-gel transition region. Fitting the linear viscoelasticity (LVE) to an analytical model developed in our previous study, we found necessity of distinguishing the intra- and interchain association in the model, with only the latter contributing to the gel formation. For the PnBA-Upy sample slightly above the gel point, the relaxation processes due to the Rouse motion and the sticker dissociation were commonly detected in the same range of T covering from 20 to 60 °C. This feature enabled us to make the time–temperature superposition separately for respective relaxation processes, and two sets of shift factors, reflecting the temperature dependence of the Rouse time τ0 and dissociation time τs, were obtained accordingly. The T dependence of the ratio of these shift factors, being identical to the dependence of τs/τ0, enabled determination of activation energy of the sticker dissociation. This activation energy was found to be consistent with that determined from the model fitting of the LVE data. The dielectric measurements detected both segmental α relaxation and an ionic α2 relaxation processes. The α2 relaxation time was found to be shorter than τs, and this result was discussed in relation to a difference between fluctuation and dissociation of ionic pairs.

The linear viscoelastic (LVE) behavior of oligomeric sulfonated polystyrene ionomers (SPS) and binary blends of two SPS ionomers with different sulfonation levels and cations was compared to the predictions of the reversible gelation model for the rheology of ionomers [ Macromolecules 2015, 48, 1221−1230]. Binary blends had the same gel point as the neat ionomer components if a linear mixing rule was used to calculate an average sulfonation level for the blend. The binary blends, however, exhibited a broader relaxation time distribution than the neat ionomers having the same number density of ions. A linear mixing rule for the ionic dissociation frequency of the blend was proposed, and when incorporated into the reversible gelation model, reasonable predictions of the terminal relaxation time of the blends were achieved.

•A facile strategy to tune block copolymer morphologies is presented by using polyoxometalate macroions as electrostatic additives.•Polyoxometalate macroions can interrupt the regularity of PS-b-P4VP to form disordered bicontinuous morphologies.•The incorporated polyoxometalate macroions can tune the thermal and viscoelastic properties of PS-b-P4VP.Bicontinuous block copolymer morphologies can offer unique transporting properties in catalysis and energy materials, whereas they are difficult to be obtained due to the relatively narrow window in phase diagram. In this work, we present a facile strategy to induce block copolymers to form bicontinuous morphologies by using nanoscale ionic clusters as electrostatic additives. A Keggin-type polyoxometalate cluster, H4SiW12O40 (SiW) was incorporated into the matrices of a series of poly(styrene-b-4-vinylprydine) (PS-b-P4VP) through the electrostatic interaction between SiW and P4VP chains. Upon the increase of SiW content, disordered bicontinuous morphologies were evolved from the PS-b-P4VP with an initial cylindrical phase, accompanying with the disappeared Tg of P4VP and the mechanical reinforcement of PS-b-P4VP/SiW nanocomposites. The bicontinuous structures can also be induced by other polyoxometalate clusters with different charges. However, the PS-b-P4VP with an initial isolating spherical phase retains their spherical structures in spite of loading SiW. These results demonstrate a new concept to obtain bicontinuous polymeric structures by using inorganic macroions to interrupt the regularity of percolating block copolymer phase, which may favor the fabrication of transporting membranes and solid electrolyte materials based on block copolymers.