Then, a second synthesis step was carried out to add alkyl chain ends that could both promote additive dispersion in the matrix, but also increase the free volume between polymer chains and thus their mobility. To this end, a fast conversion reaction of PHO-diol to PHO-hexyl was carried out with HI under stoichiometric, solvent-free conditions. The structure of PHO-hexyl was confirmed by 1 H NMR (SI, Figure ).