On the morphology and crystallization kinetics of monodisperse polyethylene oligomers crystallized from the melt

The melt crystallization of three monodisperse paraffins, C294H590, C246H494 and C198H398, has been studied optically as a function of temperature. In both C294H590 and C246H494, a distinct minimum in the rate of crystal growth has been observed, corresponding to a transition from predominantly chain-extended crystallization at high temperatures to the growth of crystals in which the molecules adopt a once-folded conformation. This change in molecular conformation is accompanied by a change in optical texture. Well below the minimum, morphologies, are spherulitic and closely resemble polyethylene. When crystals contain chain-extended molecules, highly birefringent, coarse lamellar textures develop. In C198H398, no minimum in the crystal growth rate has been observed; this system does, however, exhibit similar morphological trends to those seen in C294H590 and C246H494. Copyright (C) 1996 Elsevier Science Ltd.