DSC ANALYSIS OF ETHYLENE 1-BUTENE COPOLYMERS OBTAINED WITH DIFFERENT ZIEGLER-NATTA CATALYSTS

The crystallization and melting behaviour of two sets of ethylene/1-bu tene copolymers have been analysed by DSC. The samples, with comonomer content in the range from 0 to 21.5 mol %, were obtained by industria l processes using both Mg/Ti-based and Ti/V-based catalyst systems. Th e composition dependences of melting and crystallization temperatures were found to be strictly affected by the catalyst type. Moreover, log arithmic plots of the melting and crystallization enthalpy as a functi on of the ethylene content (mol%) in the copolymers fitted linear rela tionships whose slopes have been related to the critical sequence leng th of crystallizable ethylene units, depending on the catalytic system . These results are compared with those reported in the literature for ethylene/1-butene copolymers synthesized by other catalysts and are a ccounted for by a different distribution of the comonomer units in the macromolecules of the two sets of samples.