# Porous Organic Polymers-Supported Metallocene Catalysts for Ethylene/1-Hexene Copolymerization
## 1 Introduction  
Since the discovery of catalysts for olefin polymerization by [PERSON], [PERSON], and [PERSON] in the 1950s, the production of polyolefins has continuously grown and the research in this field has remained very competitive [1]. The development of well-defined molecular catalysts giving access to fine control of the polymerization has allowed the preparation of polyolefins with improved properties and original materials [1, 2]. Metallocene complexes have proved to be attractive catalysts for olefin polymerization, due to the possibility of influencing the catalyst activity and tailoring the properties of polyolefins such as the polymer molecular weight, comonomer incorporation, and stereospecificity by simply changing the structure of the ligands used [3].  
In order to fulfill important requirements such as the control of product morphology, prevention of reactor fouling, and control of the catalyst cost for slurry or gas-phase process [4, 5], immobilization of the metallocenes on suitable supports is necessary. Numerous studies on inorganic supports (MgCl\({}_{2}\), MgF\({}_{2}\), Al\({}_{2}\)O\({}_{3}\), molecular sieves, zeolite, and clays) and immobilization procedures havebeen investigated [6; 7; 8; 9; 10; 11; 12; 13; 14]. However, these supports suffer from several drawbacks, including the need for complex chemical treatments to get rid of acidic groups on their surfaces and to obtain appropriate particle morphology, and the presence of residual inorganic fragments within the produced polyolefins that may affect their mechanical and optical properties [15; 16; 17; 18; 19]. In contrast, porous organic polymer (POP) supports offer significant advantages over their inorganic equivalents: they provide a much closer analogue to the environment prevailing in homogeneous polymerization, do not require fastidious pre-treatment, and should not significantly affect the final polyolefin properties [9; 20; 21; 22]. Furthermore, porous organic polymers can be properly designed and synthesized with tunable pore size distribution, flexible synthetic strategy, and readily modifiable functionality [23; 24; 25; 26; 27; 28; 29; 30; 31].  
However, understanding structure/polyolefin properties relationships in these heterogeneous metallocene catalysts are nearly focused on metallocene complexes and activators, and little attention has been paid to the selection of supports for metallocene catalysts. In a previous work, we reported that the chain length of homo-polyethylene (PE) can be tuned by the pore structure of the nanoporous organic polymer supports [32]. Therefore, it is a simple, useful, and complementary method tothe metallocene complexes/activators systems to control the molecular structure of polyolefin--especially for ethylene/\(\alpha\)-olefin copolymers--by designing or tailoring the pore structure of the used POP supports. To obtain high-performance ethylene/\(\alpha\)-olefin copolymers by designing suitable metallocene/methylaluminoxane (MAO)@POPs systems, there is a need to understand how the pore structure influences the molecular structure (e.g., molecular weight, molecular weight distribution, comonomer(s) incorporation, and chemical composition distribution--CCD), which are highly related to the physical performance of products made with an ethylene/\(\alpha\)-olefin copolymer [33].  
In the recurrent paper, ethylene/1-hexene copolymerization was conducted using a 2-hydroxyethylmethacrylate (HEMA)-functionalized POPs-supported (\(n\)-BuCp)\({}_{2}\)ZrCl\({}_{2}\)/MAO/metallocene system. We investigated how the molecular chain length, molecular weight distribution, branching degree, and thechemical composition distributions of the produced ethylene/1-hexene copolymer were influenced by the active species scattered in the POPs-supported metallocene catalysts with well-defined pore structure.