Wenpeng Zhao

A sulfur-crosslinkable, elastomeric branched poly(propylene–diene) copolymer with well-regulated chain parameters was prepared using a new class of α-diimine nickel complexes, thereby serving as an alternative to traditional EPDM.

Coordination chain transfer polymerization (CCTP) has emerged as an efficient and controllable polymerization strategy that also allows for efficient in situ end-functionalization of polydienes through the highly reactive metal–carbon bonds that are generated during the CCTP process. Despite substantial progress in CCTP chemistry, reviews focusing specifically on its application to diene monomers—and particularly on its effectiveness in producing end-functionalized polydiene elastomers—remain scarce. To address this gap, this review summarizes the advances achieved over the past decade in the end-functionalization of polydienes via CCTP. We begin with a brief overview of the fundamental principles and core mechanisms of CCTP, followed by a systematic discussion of functionalization strategies for key diene monomers, including isoprene and butadiene. Finally, we highlight the existing challenges in this field and provide our perspectives on future research directions.

A family of titanium complexes (Ti1–Ti7) with the general formula LTiCl_3, supported by tridentate phenoxyimine [O⁻NO] ligands (L1–L7) bearing bulky sidearms, were synthesized by treating the corresponding ligands with stoichiometric amount of TiCl₄. All the ligands and complexes were well characterized by ¹H and ¹³C NMR spectroscopies, in which ortho- methoxyl groups on N-aryl moieties shifted to downfield, corroborating the successful coordination reaction. Structural optimization by DFT calculations revealed that one of the phenyl groups on dibenzhydryl moiety could form π-π stacking interaction with the salicylaldimine plane, because of which the obtained titanium complexes revealed good thermal stabilities for high-temperature polymerization of ethylene. The thermal robustness of the complexes was closely related to the strength of π-π stacking interactions, which were mainly influenced by the substituents on the dibenzhydryl moieties; Ti1, Ti4 and Ti5 emerged as the three best-performing complexes at 110 °C. With the aid of such π-π stacking interactions, the complexes were also found to be active at >150 °C, although decreased activities were witnessed. Besides homopolymerizations, complexes Ti1–Ti7 were also found to be active for the high-temperature copolymerization of ethylene and 1-octene, but with medium incorporation percentage, demonstrating their medium copolymerization capabilities.

A family of half-titanocene complexes bearing π,π-stacked aryloxide ligands and their catalytic performances towards ethylene homo-/co- polymerizations were disclosed herein. All the complexes were well characterized, and the intermolecular π,π-stacking interactions could be clearly identified from single crystal X-ray analysis, in which a stronger interaction could be reflected for aryloxides bearing bigger π-systems, e.g., pyrenoxide. Due to the formation of such interactions, these complexes were able to highly catalyze the ethylene homopolymerizations and copolymerization with 1-hexene comonomer, even without any additiveson the aryloxide group, which showed striking contrast to other half-titanocene analogues, implying the positive influence of π,π-stacking interaction in enhancing the catalytic performances of the corresponding catalysts. Moreover, it was found that addition of external pyrene molecules was capable of boosting the catalytic efficiency significantly, due to the formation of a stronger π,π-stacking interaction between the complexes and pyrene molecules.

A new alternative for accessing metal–ligand containing polymers via coordination insertion copolymerization of 1-hexene and ligated α-olefin is disclosed herein. To overcome the deactivation of active species by heteroatoms, the present study employed a less electrophilic late transition metal complex, and efficient copolymerizations were successfully achieved, giving rise to poly(1-hexene) elastomers containing a benzimidazolyl quinoline ligand up to 5.77%. Moreover, the copolymerization displayed a living nature, demonstrating a capability of control over the molecular weights and molecular weight distribution. Coordination of the obtained ligated poly(1-hexene) elastomers with metal ions produced polymer networks with the ligand–metal complexes as crosslinkers and thus led to a significant enhancement of the mechanical properties of the resultant materials.