Poly(3-phenyl-4-oxybiphenylene-4’-carbonyl) (PPOBC) and poly(5-phenyl-2-oxy-6-naphthoyl) (PPONY) have been prepared as lamellar single crystals using the confined thin film melt polymerization technique. Electron diffraction indicates a monoclinic (pseudo-orthorhombic, alpha = 90 degrees C) cell with a = 15.24 Angstrom, b = 3.94 Angstrom and c = 10.54 Angstrom for PPOBC and an orthorhombic cell with a = 29.60 Angstrom, b = 5.08 Angstrom and c = 16.74 Angstrom for PPONY (1 Angstrom = 0.1 nm). Modelling using the Cerius(2) program suggests a Pn11 space group for PPOBC and a P2(1)/c2(1)/c2/n space group for PPONY. In contrast to the relatively low crystal-mesophase transition temperature (T-k-m = 350 degrees C) for poly(phenyl-p-phenylene terephthalate), in which the phenyl rings would be expected to be randomly positioned on the p-phenylene residues, the regular conformations in these two polymers lead to high T-k-m (422 degrees C for PPOBC and 528 degrees C for PPONY).