Using a structural model for a similar comb-like polymer (Figure ), we assigned 24 reflections to the distances of repeating interlayers. Following our PXRD analysis, protonation with a strong acid (PEI-C16-H + ) contracted the interlayer distances more than in the pristine sample (PEI-C16). This contraction is less pronounced in the post-desalination sample (PEI-C16-Cl), suggesting that ion association and pH influence this behavior. The contraction reaches 12% for distance L0 and 8% for L1 in PEI-C16-H + and 7% for L0 and 3% for L1 in the PEI-C16-Cl. A small reflection peak was observed for the interlayer distance L2 in PEI-C16.