Segmented poly(tetramethylene oxide) zwitterionomers and their homologous ionenes. 2. Phase separation through DSC and solid state 1H-NMR spectroscopy
Résumé
Phase separation has been quantitatively analyzed through DSC and solid state 1H-NMR spectroscopy (line shape and T1ρ analysis) on a series of segmented PTMO zwitterionomers carrying dipolar functions of the ammoniopropanesulfonate or ethoxydicyanoethenolate type and of their analogous ionenes. All the amorphous copolymers (Mn0(PTMO segment) < 3 × 103) display a typical biphasic structure characterized by a strongly predominant soft matrix of pure PTMO (TgS = -77 °C) and polar hard domains (TgH = -5 to 40 °C) where all the polar junctions are concentrated and where every polar unit locks and rigidifies about the two or three vicinal PTMO monomeric units. The thermal stability of the polar aggregates which persist at temperatures much higher than the glass transition TgH depends on their chemical structure: for promoting high cohesion, zwitterions are much more efficient than ion pairs (zwitterionomers versus ionenes) and the ammoniopropanesulfonate function is more efficient than the ethoxydicyanoethenolate one in spite of similar dipole moments (∼25 D). Semicrystalline copolymers (Mn0(PTMO segment) > 3 × 103) still show phase separation in their amorphous state in the higher temperature range above their melting points (Tm ∼ 10-25 °C). The typical biphasic morphologies of all these copolymers may be readily interpreted within the multiplet-cluster concept revisited by Eisenberg, and the rigidification of the PTMO units immediately surrounding the polar multiplets is unambiguously evidenced in solid state NMR spectroscopy. The specific segmented chain topology results, however, in an earlier (lower polar unit contents) and far better phase separation than in similar statistical copolymers.