Crystallinity and amorphous segmental properties in random propylene-ethylene copolymers: NMR correlation

We present a characterization of the state of semi-crystallization of rando m propylene-ethylene copolymers, observing the transverse relaxation of pro tons attached to the chains. The degree of crystallinity was determined ste p by step, from NMR, during the progressive annealing of the copolymers, qu enched at room temperature from the melt. The ethylene content varied over the range 0-4.7 (w/w). It is shown that the empirical temperature dependenc e of the degree of crystallinity, as detected by NMR, obeys a single curve; this curve is translated along the temperature axis in accordance with the melting point depression when the ethylene content varies. The degree of c rystallinity is primarily a function of the undercooling, whatever the ethy lene content. Considering any state of semi-crystallization, a strong corre lation between the degree of crystallinity and the relaxation rate of the p rotons attached to amorphous segments is established; the NMR sensitivity t o crystallinity is considerably enhanced when detected by amorphous propert ies. (C) 1999 Society of Chemical Industry.