Crystal structure and morphology of bromo‐substituted fully aromatic liquid crystal polyesters

Abstract

AbstractThe bromo‐substituted main chain liquid crystal polyesters poly(3‐bromo‐4‐oxybiphenylene‐4′‐carbonyl) (PBOBC) and poly(5‐bromo‐6‐oxy‐2‐naphthoyl) (PBONY) have been polymerized as lamellar single crystals using the confined thin film melt polymerization (CTFMP) technique. Electron diffraction indicates a triclinic (pseudo‐orthorhombic) unit cell with a12.71, b3.85, c10.50 Å, αβγ90° for PBOBC and a monoclinic unit cell with a13.02, b4.06, c17.15 Å, β101° for PBONY. The crystal structures of the two polymers have been simulated by the Cerius2 program and are suggested to have space group P for PBOBC and space group P121/c1 for PBONY. DSC measurements indicate that these two bromo‐substituted fully aromatic polyesters have crystal‐mesophase transition temperatures (Tk‐m389°C for PBOBC and 429°C for PBONY) with TGA indicating the onset of degradation at similar temperatures (400 and 420°C). The Tk‐m are between those of the corresponding non‐substituted and phenyl‐substituted aromatic polyesters. Possible reasons for the Tk‐m differences are considered in detail.