Compatibility and mesophase separation in blends of α‐helical polyglutamates

Abstract

AbstractBlends composed of the α‐helical polymers, poly‐L‐glutamates [(NHCαHRC′O)n, R = CH2CH2COO(CH2)m(C6H5] (Lm) and the corresponding D enantiomers (Dm), have been studied by x‐ray diffraction and viscoelastic measurements. Binary blends of L2, D2, L3, and D3 are compatible and form isomorphous mixed crystals at all compositions, whereas other pairs, with the exception of L1/D1, are incompatible. The demixing process is described for a ternary system consisting of L1, D3, and a diluent chloroform at 40°C. The phase diagram comprises four regions, I, IA, A, and AA, with increasing polymer concentration; I: isotropic, A: anisotropic, IA: I–A biphasic, and AA: A–A biphasic. The IA biphasic gap is greater in the ternary system than in the binary ones. The high‐molecular‐weight component (D3) is partitioned into the A phase in the IA region. The AA separation originates from incompatibility of the polymers. The phase behavior is discussed on the basis of the Abe‐Flory theory by incorporating the polymer‐polymer interaction parameter.