MORPHOLOGY OF HOMOGENEOUS COPOLYMERS OF ETHENE AND 1-OCTENE .1. INFLUENCE OF THERMAL HISTORY ON MORPHOLOGY

The morphology of homogeneous copolymers of ethene and 1-octene synthe sized using a V-based Ziegler-Natta catalyst was studied as a function of the short chain branching content( SCBC) and the molar mass. Linea r polyethylenes (LPE) were used as reference material. For the linear samples an increase in molar mass results in an increase of the long p eriod and the crystalline lamella thickness. A decrease of cooling rat e results in an increase of the melting temperature, the long period a nd the crystalline lamella thickness and an evolution from spherulitic structures to perfectly stacked lamellae. For the branched samples, i ncreasing the SCBC results in a decrease of the melting and the crysta llization temperature, crystallinity, spherulite radius, the long peri od, and the crystalline lamella thickness. The two latter tend to a li miting value on reaching a SCBC of 20CH(3)/1000C. On the other hand, a n increase of the a axis and to a lesser extent the b axis of the unit cell is observed. Decreasing the cooling rate affects only the crysta llinity of the least branched samples. Furthermore decreasing the cool ing rate results in smaller spherulites, has a minor influence on the lamellar parameters and reduces the dimensions of the basal plane of t he unit cell. Increasing the molar mass of the branched samples result s in a drop of the crystallinity, a deterioration of the superstructur e, enlarges the amorphous layer thickness and the dimensions of the ba sal plane. All these observations can be accounted for by the differen t crystallization regimes being applicable when different molar masses , SCBC and cooling rates are used. (C) 1997 John Wiley & Sons, Inc.