Supramolecular structure of liquid-crystalline polyesters in triclinic cell

We have analyzed the phase behavior of a series of liquid-crystalline polyesters bearing the n-alkoxy pendant group. For n = 1-4, this class of polymers shows a crystalline phase, called phase I, with a layered molecular packing and two chains per unit cell. For n > 4, a new molecular packing is observed. The new phase, called phase II, is characterized by the supramolecular assembly of 10-12 chains, each structurally independent of the others. This assembly is located in a large triclinic cell: in the case of P(5), the cell parameters are a = 18.67 Angstrom, b = 17.54 Angstrom, c = 21.23 Angstrom, alpha = 111. 1degrees, beta = 81.7degrees, and gamma = 105.5degrees, with 10 chains per unit cell (d(caled) = 1.23 g cm(-3)). The molecular packing of phase II is well-described in terms of a "fracture" of the layered molecular structure of phase I. This fracture is restored when samples are dipped into chlorinate solvents, The reason the packing fracture of phase I occurs is hot clear: we believe that a complex balance between "packing incompatibility" of rigid chains and flexible side groups might be responsible for this phenomenon.