Controlling Surface and Crystalline Lamellar Morphologies of Nascent Poly(ethylene-alt-CO) Under Different Polymerization and Thermal Conditions

Through the tailoring of the polymerization conditions, using palladium(II)-based metal catalysts coordinated by 1,3-bis(diphenylphosphino)propane, it is feasible to synthesize highly crystalline nascent poly(ethylene-alt-CO) directly into its α and β crystal polymorphs. Crystallization during polymerization in the α or the β polymorph and the resultant surface morphology of the nascent poly(ethylene-alt-CO) are found to be strongly dependent on the polymerization conditions. While at the low polymerization temperature, the α-phase is preferred, at the high polymerization temperature predominantly crystals having the β-phase are obtained. The surface and crystalline morphology of the nascent polyketone is studied using scanning electron microscopy (SEM), differential scanning calorimetry (DSC), wide angle X-ray diffraction (WAXD), small angle X-ray scattering (SAXS), Fourier transform infrared (FTIR), and solid-state nuclear magnetic resonance (NMR) spectroscopy. Electron diffraction studies, on different nascent polyketone samples, confirmed the formation of single crystals during polymerization at varying polymerization conditions. The growth of single crystals, during polymerization, is suggestive of the direct attachment of the growing chains on the formed nucleus at a high supercooling. The nascent single crystals, having perfectly alternating poly(ethylene-alt-CO) molecular structures, are found to aggregate in different morphologies that are induced by the polymerization conditions. Solid-state ¹³C NMR spectroscopy and FTIR studies confirm that the thermal stability of the synthesized poly(ethylene-alt-CO) is dependent on the crystalline phase obtained during polymerization; the crystals formed in the high entropy β-phase are found to be thermally more stable than those in the α-phase. The thermal stability of the melt crystallized samples, obtained after melting and recrystallization of the nascent crystals, is also found to be dependent on the origin of the crystal polymorph.