Structure characterization of copolymers of ethylene and 1-octadecene

Four ethylene-1-octadecene copolymers and the corresponding polyethylene ho mopolymer, synthesized with a metallocene catalyst, have been analyzed by u sing three characterization techniques in the solid state: differential sca nning calorimetry, wide-angle X-ray diffraction, and Raman spectroscopy. Ve ry important annealing effects are observed in the copolymers with higher c omonomer content while standing at room temperature, in such a way that the enthalpies of melting derived from the first and second melting are differ ent. The X-ray diffractograms have been analyzed in terms of amorphous and crystalline components, determining both the crystallinity and the position of the different reflections. The variation of the unit cell parameters ha s been calculated from those reflections. No indication of a possible parti cipation of the relatively long 1-octadecene branches in the crystallizatio n can be deduced from the X-ray data. The degree of crystallinity has also been determined from the Raman spectra, following two procedures. The resul ts indicate that the crystallinities deduced from the band at 1416 cm(-1) a re much lower than those derived from the other two characterization techni ques. On the contrary, the data from the 1060 cm(-)1 band are practically c oincident with the X-ray determinations. (C) 2000 John Wiley & Sons, Inc.