For ionomers, unfavorable interaction between highly polar ion pairs and the low polarity polymer medium leads to ion aggregation. In contrast, for polyelectrolytes, the counterions prefer solvation in the polar medium to leave the chain charged and accordingly stretched due to the charge repulsion. In this study, linear viscoelastic and dielectric properties of mixtures of two ionomers with high dielectric constant low volatility plasticizers were examined. The ionomer chains having bulky side chains are not entangled. Upon increasing the plasticizer content, the terminal relaxation is significantly accelerated due to two effects: (1) a plasticizing effect lowering the T g and (2) a higher dielectric constant that softens the ionic interactions, leading to ionic dissociation into isolated pairs that further boosts the static dielectric constant at low frequency/long time. A model incorporating these two mechanisms and utilizing a dielectric constant εC, after the nonionic segmental α relaxation as the relevant dielectric constant for ion dissociation, predicts quantitatively the accelerated dynamics, as ionomers transition to polyelectrolytes on dilution.

Nitroxide-mediated polymerization (NMP) affords the synthesis of well-defi ned ABA triblock copolymers with polystyrene external blocks and a charged poly(1-methyl-3-(4-vinylbenzyl)-imidazolium bis(trifl uoromethane sulfonyl)imide central block. Aqueous size-exclusion chromatography (SEC) and 1 H NMR spectroscopy studies confi rm the control of the composition and block lengths for both the central and external blocks. Dynamic mechanical analysis (DMA) reveals a room temperature modulus suitable for fabricating these triblock copolymers into electroactive devices in the presence of an added ionic liquid. Dielectric relaxation spectroscopy (DRS) elucidates the ion-transport properties of the ABA triblock copolymers with varied compositions. The ionic conductivity in these single-ion conductors exhibits Vogel-FulcherTammann (VFT) and Arrhenius temperature dependences, and electrode polarization (EP) analysis determines the number density of simultaneously conducting ions and their mobility. The actuators derived from these triblock copolymer membranes experience similar actuation speeds at an applied voltage of 4 V DC, as compared with benchmark Nafi on membranes. These tailorable ABA block copolymers are promising candidates for ionic-polymer device applications.

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.

Reversible addition–fragmentation chain transfer (RAFT) polymerization enabled the synthesis of well-defined A–BC–A triblock copolymers containing a synergy of pendant ether and imidazolium sites.