M.E. Shivokhin, C.R. López-Barrón, P. Brant
Keywords: polyolefins, compatibilizers, comb block, copolymer
Summary:In this talk I will introduce a novel class of olefin-based block copolymers with hyper-branched comb block (CB) architecture. The starting material for the CB synthesis is ESCOR 5100, a long-chain branched random copolymer of ethylene and acrylic acid (EAA), hydroxyl-terminated (atactic or isotactic) polypropylene (from vinyl-terminated macromonomers) are grafted to the EAA by esterification to produce the hyperbranching structures. Small-angle X-ray scattering (SAXS) measurements, in the melt, reveal nano-segregation of the PP side chains from the EAA backbone, which results in remarkable enhancement in linear viscoelastic and extensional flow properties. Both the elastic and viscous moduli in the terminal regime increase as a function of PP side chain length and weight fraction. A second (low frequency) elastic modulus plateau is observed in CBs with high PP side chains (>40 wt%), suggesting formation of a weak network made of EAA chains connecting PP segregated domains. This network formation has a strong effect on the non-linear response of the CBs, namely, a very large extensional strain-hardening is observed. The strain hardening strength (measured at Hencky strain of 2.5) increases from values of ~3, for the neat EAA polymers, to ~100, for some EAA-cb-PP. It is proposed that the many PP-cb-EAA interfacial junctions per chain are responsible for the enhanced strain hardening compositions. Apart from demonstrated significantly enhanced processability these comb-block copolymers can potentially be used as compatibilizers for post-consumer polyolefin mixtures to unlock high-value applications, which is in alignment with the Exxonmobil sustainability efforts.