Nanoscale layers of precise ion-containing polyamides with lithiated phenyl sulfonate in the polymer backbone

We investigate a new series of precise ion-containing polyamide sulfonates (PASxLi), where a short polar block precisely alternates with a non-polar block of aliphatic carbons (x = 4, 5, 10, or 16) to form an alternating (AB)n multiblock architecture. The polar block includes a lithiated phenyl sulfonate in the polymer backbone. These PASxLi polymers were synthesized via polycondensation of diaminobenzenesulfonic acid and alkyl diacids (or alkyl diacyl chlorides) with x-carbons, containing amide bonds at the block linkages. The para- and meta-substituted diaminobenzene monomers led to polymer analogs denoted pPASxLi and mPASxLi, respectively. When x ≤ 10, the para-substituted diamine monomer yields multiblock copolymers of a higher degree of polymerization than the meta-substituted isomer, due to the greater electron-withdrawing effect of the meta-substituted monomer. The PASxLi polymers exhibit excellent thermal stability with less than 5% mass loss at 300 °C and the glass transition temperatures (Tg) decrease with increasing hydrocarbon block length (x). Using the random phase approximation, the Flory-Huggins interaction parameter (χ) is determined for pPAS10Li, and χ (260 °C) ∼ 2.92 reveals high incompatibility between the polar ionic and non-polar hydrocarbon blocks. The polymer with the longest hydrocarbon block, pPAS16Li, is semicrystalline and forms well-defined nanoscale layers with a spacing of ∼2.7 nm. Relative to previously studied polyester multiblock copolymers, the amide groups and aromatic rings permit the nanoscale layers to persist up to 250 °C and thus increase the stability range for ordered morphologies in precise ion-containing multiblock copolymers.