DYNAMIC DSC, SAXS AND WAXS ON HOMOGENEOUS ETHYLENE-PROPYLENE AND ETHYLENE-OCTENE COPOLYMERS WITH HIGH COMONOMER CONTENTS

Ethylene-propylene (EP) and ethylene-octene (EO) copolymers polymerize d with the aid of homogeneous vanadium and metallocene catalysts were compared by DSC and time-resolved simultaneous SAXS-WAXS-DSC at scanni ng rates of 10 and 20 degrees C min(-1) using synchrotron radiation. A n EP copolymer with a density of 896 kg m(-3) (about 89 mol% ethylene) after compression moulding gave orthorhombic WAXS reflections. The cr ystallinity as a function of temperature [w(c)(T)] calculated from the se reflections using the two-phase model was in good agreement with w( c)(T) calculated from c(p) measurements using DSC, The c(p) measuremen ts also enabled calculation of the baseline c(p) and the excess c(p). The SAXS measurements revealed a strong change in the long period in c ooling and in heating. The SAXS invariant as a Function of temperature showed a maximum in both cooling and heating, which could be explaine d from the opposing influences of the crystallinity and the electron d ensity difference between the two phases. Two EO copolymers with densi ties of about 871 kg m(-3) (about 87 mol% ethylene) no longer showed a ny clear WAXS reflections, although DSC and SAXS measurements showed t hat these copolymers did crystallize. The similarity between the resul ts led to the conclusion that the copolymers, though based on differen t catalyst systems - vanadium and metallocene - did not have strongly different sets of propagation probabilities of chain growth during pol ymerization. On the basis of a Monte Carlo simulation model of crystal lization and morphology, based on detailed knowledge of the microchain structure, the difference between WAXS on the one hand and DSC and SA XS on the other could be explained as being due to loosely packed cry: tallized ethylene sequences in clusters. These do cause the density a nd the electron density of the cluster to increase (which is measurabl e by SAXS) and the enthalpy to decrease (which is measurable by DSC) b ut the clusters are too small and/or too imperfect to give constructiv e interference in the case of WAXS. Of an EP copolymer with an even lo wer ethylene content (about 69 mol%), the crystallization and melting processes could still be readily measured by DSC and SAXS, which prove s that these techniques are eminently suitable for investigating the c rystallization and melting behaviour of the copolymers studied.