The effect of multi-block structure on the crystallization and properties of ethylene/1-octene copolymers from chain shuttiling technology.

The crystallization properties, the morphology at nanometric length scale and the tensile properties of ethylene/1-octene multi-block copolymers (EOBCs) obtained from chain shuttling technology are analyzed. The samples are characterized by a statistical multi-block architecture, where soft and amorphous blocks with high octene concentration (≈18.9mol%) alternate with hard and crystalline blocks with low octene concentration (≈0.5mol%). A set of samples with similar octene concentration in the hard and soft blocks, fraction of hard blocks and melting temperature of ≈120°C, but different average length of the blocks and average number of blocks/chain are selected.
We show that the crystallization properties of EOBCs and the structural organization of the chains which develops by effect of crystallization are strongly influenced by the multiblock architecture, the tendency of the hard blocks to crystallize in separated domains, the short and polydisperse length of the hard blocks and the steric constrains imposed by the covalent bonding between the hard and soft blocks. This results in a hierarchical structural organization which is articulated over different length scales, involving the stacking of the chain folded lamellae in separated domains at lamellar length scale, and the relative arrangement of the hard domains in the compliant matrix populated by the soft blocks, at the scale of domain spacing.
The block architecture also influences the mechanical properties. The samples, in spite of similar octene concentration, molecular mass and fractional content of hard blocks, show remarkable differences of mechanical properties, which reflect differences in the average block length ad number of block/chain. The achieved properties encompass those of strong elastomers, in the case of samples with low block length and high number of blocks/chain, up to reach those of soft elastomers in the case of samples with high block length and low number of blocks/chain.