The global production of synthetic plastics surpasses 380 million tonnes annually, with polyolefins accounting for half. Despite Ziegler-Natta catalysts' significant contributions, incorporating polar functional groups into polyolefins to expand their applications remains a challenge. Late-transition-metal catalysts, with their lower oxophilicity, offer better tolerance towards polar groups than early transition-metal catalysts, which are susceptible to poisoning. The polyolefin industry largely relies on heterogeneous catalysts due to their morphology control, enabling continuous polymerization and preventing reactor fouling. Homogeneous catalysts, while advantageous for mechanistic studies and structural modification, lack the industrial benefits of heterogeneous systems. Surface organometallic chemistry (SOMC) aims to bridge this gap by heterogenizing homogeneous complexes on solid supports. However, conventional heterogenization methods for olefin polymerization catalysts suffer from catalyst leaching and incompatibility with polar comonomers, particularly concerning late-transition-metal catalysts. Existing examples of heterogeneous late-transition-metal catalysts for ethylene copolymerization with polar comonomers show limited activity and comonomer incorporation. This research focuses on overcoming these limitations by developing a novel and general heterogenization strategy.

Previous approaches to heterogenizing olefin polymerization catalysts typically involved three routes: (a) introducing a precatalyst to a cocatalyst-pretreated support, (b) introducing a cocatalyst to a precatalyst-pretreated support (often avoided due to side reactions), and (c) activating the precatalyst before support impregnation (unsuitable for sensitive active species). These methods suffer from weak catalyst-support interactions, leading to leaching, especially when polar comonomers are involved. Covalent tethering, although offering stronger interactions, is complex and challenging for characterization. Existing literature on late-transition-metal-based heterogeneous systems for ethylene polymerization, particularly with polar comonomers, is limited. While some examples demonstrate copolymerization, they suffer from low activity and comonomer incorporation. This paper addresses the need for a more versatile and efficient method.

This study designed an ionic anchoring strategy (IAS) for heterogenizing transition metal catalysts. Hydroxyl-functionalized ligands were synthesized from commercially available reagents via simple reactions, including protection, lithiation, and complexation. Specifically, phosphinophenolate nickel and phenoxy-imine titanium complexes were prepared. The hydroxyl groups were then converted into sodium alkoxides (ONa). The supported catalysts were prepared by stirring the metal complex solutions with the solid supports (SiO₂, TiO₂, Al₂O₃, ZnO, MgO). The adsorption capacity of the ONa-tagged complexes was significantly higher than their OH- and non-functionalized counterparts, confirming strong ionic interactions with the solid supports. Ethylene polymerization and copolymerization studies were conducted in hydrocarbon solvents. Active site counting was performed using PMes as a poison. The influence of various solid supports on catalytic activity, polymer molecular weight, and melting point was investigated. Ethylene copolymerization studies used methyl acrylate (MA), other acrylates, trimethoxyvinylsilane, and allyl comonomers. High-temperature polymerization experiments were conducted to evaluate catalyst thermal stability. Large-scale polymerization in a 2.5 L reactor was performed to assess scalability and morphology control. Finally, polyethylene composites were synthesized in situ by using the supported catalysts and different fillers. The resulting materials were characterized for mechanical properties, thermal diffusivity, electrical conductivity, and flame retardancy. Photodegradation studies were conducted using TiO₂-supported catalysts to evaluate the efficiency of photocatalytic degradation.

The IAS significantly enhanced the activity and molecular weight of the polyethylene produced compared to their homogeneous counterparts. Active site counting revealed that approximately 95% of the nickel centers were active during ethylene polymerization. Different solid supports significantly affected catalytic activity and polymer properties; more basic supports generally led to higher activity and molecular weight. Supported nickel catalysts demonstrated high activity (up to 10⁸ g mol⁻¹h⁻¹) in ethylene polymerization even at high temperatures (150–170 °C). The supported catalysts showed higher comonomer incorporation in ethylene copolymerization with polar comonomers than their homogeneous analogs. The IAS facilitated high-temperature (100–140 °C) copolymerization with tert-butylacrylate and methyl 10-undecenoate, maintaining high activity and increasing comonomer incorporation. Large-scale polymerization yielded significant amounts of polymer in a 2.5 L reactor. In situ generation of polyolefin composites with various fillers resulted in improved material properties compared to those produced by extrusion blending. For example, the in situ generated polyethylene composites with Al₂O₃ exhibited enhanced thermal conductivity, and those with graphene demonstrated dramatically improved electrical conductivity. Flame retardancy was also significantly improved with the in situ generated composites. Importantly, photocatalytic degradation studies showed that polyethylene composites with TiO₂ supported via IAS underwent significantly faster degradation than blends, with the inclusion of polar functional groups further accelerating the process.

The IAS successfully addressed the limitations of previous heterogenization strategies for olefin polymerization catalysts. The strong ionic interactions between the ONa tag and the solid support prevent catalyst leaching and maintain catalytic activity in the presence of polar comonomers. The improved activity and comonomer incorporation observed with supported catalysts likely stem from the electronic modification of the metal center by the support. The enhanced thermal stability of the heterogeneous catalysts enables high-temperature polymerization, critical for industrial applications. The in situ generation of composites provides an efficient method for producing high-performance materials with homogeneous filler distribution, leading to superior material properties. The enhanced photodegradation of TiO₂-supported composites presents a promising approach to addressing the environmental concerns associated with polyolefin waste. The results highlight the versatility and effectiveness of the IAS for various polymerization systems and composite material synthesis.

This work presents a simple yet powerful ionic anchoring strategy for heterogenizing olefin polymerization catalysts. The method is versatile, effective, and leads to improved catalyst performance, morphology control, and the facile synthesis of high-performance polyolefin composites. This strategy offers a significant advancement in the field, paving the way for sustainable and efficient production of advanced polymer materials and addressing the challenges of polyolefin waste management. Future research could explore expanding the range of applicable metal complexes and solid supports, further optimizing catalyst design for specific applications, and investigating the detailed mechanism of the enhanced comonomer incorporation and photocatalytic degradation.

While the IAS offers significant advantages, some limitations exist. The scope of suitable polar comonomers might need further investigation to ensure broad applicability. The long-term stability of the supported catalysts under rigorous industrial conditions requires further evaluation. A deeper understanding of the interactions between the ionic tag and the solid supports is needed for further optimization and rational design of the catalysts. More detailed mechanistic studies are needed to completely understand the enhanced performance of the IAS. Finally, scaling up the composite synthesis process for mass production needs to be explored.