Coordinative polymerization brings opportunities for producing well-defined long-chain branched polyolefins specifically by using homogeneous single-site catalysts. Herein, we report a new dual catalytic system for the controlled formation of long-chain branches in a coordinative chain transfer polymerization. The growing polymers on the main aryl-substituted αdiimine nickel catalyst are frequently transferred via a chain transfer agent to the vinyl-producing catalyst, (Bipy) 2 FeEt 2 , where they are released as macromers through β-H elimination. The released macromers are incorporated into the growing polymer structure thanks to the high comonomer affinity of the main catalyst. By recurrence of this reaction cycle, a branch-on-branch structure is produced, which cannot be obtained using previous single or dual catalytic systems. The efficiency of the reaction is studied by performing ethylene and 1-hexene polymerizations at different reaction conditions. By increasing the amount of vinyl-producing catalyst, dramatic effects on the rheological properties are observed including increased dynamic moduli, prolongation of the G′−G″ crossover, and significant thermorheological complexity, all demonstrating formation of long branches. The microstructural analysis using 13 C NMR indicates that short-chain branches are vastly found in all samples due to the chain walking reaction. The spectroscopy and thermal analyses suggest that these short branches decrease by the addition of the vinyl-producing catalyst. This is presumably attributed to the high steric hindrance of the macromers, which forces the catalyst centers to preferentially attach to the primary carbons.
Plastics offer several advantages, but their production
and disposal
processes have severe environmental implications. To overcome these
issues, there is a need to switch from the linear to a circular economy
by recycling plastic waste and by utilizing renewable resources to
create bioplastics. However, this is challenging in the case of nonbiodegradable
polyolefins (POs), which form the largest fraction of produced polymers
and the least recycled one. Mechanical recycling, chemical recycling,
and PO bioplastics are the three pillars of PO circular economy. Although
mechanical recycling is an environmentally and economically viable
option, it often results in the degradation and downgrading of POs.
Nonetheless, innovations in mechanical recycling, such as the use
of (nano)fillers or compatibilization with olefin block copolymers,
attempt to mitigate these issues. Furthermore, the development of
covalent adaptable networks improves the mechanical properties of
recycled PO thermoplastics and provides recyclable PO elastomers.
If mechanical recycling fails to meet the desired characteristics
of the recyclate PO, chemical recycling to other chemicals is a potential
alternative. Although retrieving the monomer is ideal for achieving
a closed-loop circular economy, traditional approaches for the noncatalytic
chemical recycling of POs are energy-intensive and lack specificity.
This has been tried to be addressed by advancements in catalytic approaches.
Finally, biobased polyolefins, especially those produced through emerging
nonbiochemical approaches, offer attractive alternatives that can
be integrated into existing petrochemical plants. With this comprehensive
perspective on POs circular economy academic and industrial researchers
of the field can better contribute to a more sustainable future.
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