Morphological Evolution of Ionomer/Plasticizer Mixtures during a Transition from Ionomer to Polyelectrolyte

Abstract

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.

Pendant side‐chain sterics against electrostatic forces: Influencing short‐range ordering in random polyelectrolytes

“…In this regime, the value of d B ~ d L . A coexistence of the backbone–backbone spacing and cluster–cluster spacing features have also been reported recently by Zhang et al . A third regime can be observed from P4VP‐ r ‐PI_C5Br to P4VP‐ r ‐PI_C8Br, ( d B =17–21 å).…”

“…The intensity of the VDW peak has been used to correlate the fraction of other observed features in WAXS. For instance, the intensities of crystalline or ionomer peaks relative to the VDW peak intensity have been used to estimate the fraction of these morphological features in a polymer …”

“…The more rigid the polymer chains are, the less likely are these polymer chains to be distorted. Thus, the formation of ionomer cluster morphology is less likely in rigid polymers . On the other hand, the more rigid the polymer backbones are the more likely the backbone–backbone correlations between these polymer chains.…”

“…Polymers with pendant side chains and ionomers have been studied independently and extensively in the literature. However, a study on these morphologies competing, or coexisting, in a copolyelectrolyte system has received little attention in the literature.…”

“…Building on the phenomenological argument put forth by Colby, on the formation of ionomer morphology, a characteristic spacing below which dipole–dipole attraction energy is dominant can be estimated. The thermal energy, K B T , where K B is the Boltzmann's constant, and T is the temperature, is a measure of the reach of dipole–dipole attraction energy.…”