Thin film melt polymerized single crystals of poly(p‐oxybenzoate)

The morphology of poly(p‐oxybenzoate) polymerized from p‐acetoxybenzoic acid (pABA) in constrained thin films at temperatures between 130°C and 315°C for various times is described. Polymerization below the melting point of the monomer, 196°C, occurs by a sublimationrecrystallization‐melting process, with polymerization occuring in the melt. Lamellar crystals, often bilayered, are found that are ca. 100 Å thick as well as single disclination domains. Electron diffraction patterns indicate the presence of either phase I or II in a given crystal, with the unit cell for phase II being proposed; the molecular axes are normal to the lamellae. Polymerization above 200°C results in holes in the lamellae; it is suggested that polymerization also is in the form of lamellae followed by the hole formation as further reaction occurs in the crystalline state, initial “crystal” growth at all temperatures is in the liquid crystalline state.