F. Auriemma, C. De Rosa, M. Scoti, G. Talarico
Dipartimento di Scienze Chimiche, Università di Napoli Federico II, Complesso Monte Sant’Angelo, via Cintia, 80126 Napoli.
The crystallization properties, morphology and elastomeric behavior of some ethylene/1-octene multi-block copolymers produced by chain shuttling technology  are analyzed. We evidence that the samples consist of a reactor blend of chains characterized by alternation of crystalline (hard) blocks with low octene content and amorphous (soft) blocks with high octene content, having different length and different number of blocks. The sample show similar degree of crystallinity and melting temperature, and good elastomeric properties at 25°C. Differences occur for the crystallization temperature, morphology and elastomeric properties at 60°C. These differences reflect differences in segregation strength. For samples containing a high fraction of chains with hard-blocks of short length, and long soft-blocks, the segregation strength is high, and the hard domains are well separated at high correlation distances. For samples containing a high fraction of chains characterized by long hard-blocks and short soft-blocks some kind of interpenetration of the hard segments in the soft domains occurs, with consequent decrease of segregation strength and interdomain distance. Since the long hard-segments can also connect different hard-domains, a well interpenetrated network is formed. Therefore, the samples forming an interpenetrating network crystallize at lower temperatures (more slowly), show high mechanical strength and ductility, and good elastomeric properties even at high temperatures. The samples with no inter-woven structure with short hard-blocks, instead, form a more heterogeneous morphology, show low mechanical strength and lose elastomeric properties already at 60°C.
 D.J. Arriola, E.M. Carnahan, P.D. Hustad, R.L. Kuhlman, T.T Wenzel, Science, 312, 714 (2006). (link)