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Prof. Chen Yile's group at the University of Science and Technology of China realizes copolymerization of olefins and polar internal olefins
2020-01-07 Source: Polymer Technology

Polyolefins are usually saturated, which makes many properties of polymers such as printability, dyeability, etc. relatively poor. The introduction of a small amount of polar monomers in the polyolefin chain, such as vinyl chloride, vinyl ether, vinyl acetate, acrylate, etc., can greatly improve the surface properties, adhesion, flexibility, solvent resistance, Rheological properties, as well as miscibility and miscibility with other polymers and polymer materials. The coordination copolymerization of olefins and polar monomers through transition metal catalysts has great potential in the preparation of functionalized polyolefins. However, the realization of this process is very challenging and is also considered to be one of the last "holy grail" in the polyolefin field. Compared to simple mono-substituted polar olefins, the polymerization of 1,2-di-substituted polar internal olefin monomers is more challenging.

Recently, the research group of Professor Chen Zile of the University of Science and Technology of China has developed a direct copolymerization method of palladium catalyst and a series method of metathesis and palladium-catalyzed copolymerization. Functionalized polyolefin material.

In recent years, transition metal catalysts have been involved in catalyzing the copolymerization of ethylene with polar monomers to produce functionalized polyolefins (Figure 1). From the figure they found that these monomers are based on simple olefin-terminated polar monomers. In order to further expand the range of polar monomers, the art also needs to develop polar comonomers that have not been covered in existing reports to obtain new functionalized polyolefins. At the same time, in order to further reduce production costs, in the selection process of polar monomers, we need to try to select those polar comonomers that are cheap and readily available, especially polar monomers that can be obtained from biomass sources. Therefore, their research focused on 1,2-disubstituted polar internal olefin monomers derived from biomass.

Figure 1. Transition metal catalyzed preparation of functionalized polyolefins: development of polar monomers.

Due to the large steric hindrance of 1,2-disubstituted polar internal olefin monomers (methyl crotonic acid, ethyl cinnamate, dimethyl maleate, etc.), the process of choosing to directly catalyze their copolymerization with ethylene requires The following conditions are satisfied: the catalyst has a strong tolerance to polar functional groups; the catalyst steric hindrance must be moderate; the catalytic system does not have a chain walking mechanism. Through analysis, they chose the phosphine-palladium sulfonate catalyst PO-Pd , which has developed rapidly in recent years, and this type of catalyst can just meet the above conditions.

Through screening, PO-Pd can catalyze the copolymerization of 1,2-disubstituted polar internal olefin monomers (methyl crotonic acid, ethyl cinnamate, dimethyl maleate, etc.) with ethylene, thereby preparing a new type of Functionalized polyolefin. The number average relative molecular weight of the prepared polar polyolefin material is between 1300-10400, and the insertion ratio of the polar monomer is between 1.1-3.4% (Figure 2). In particular, compared with conventional polar copolymers, the polymer chains of such copolymers each have a substituent on two adjacent carbons in the polar monomer insertion region. In particular, for the dimethyl maleate monomer, an adjacent polar carbon functional group is attached to each of the adjacent carbons of the polar region of the copolymer structure. This special copolymer is similar to the classic ethylene- Compared with methyl acrylate copolymer, water contact angle and adhesion performance are greatly different and improved.

Figure 2. PO-Pd directly catalyzes the copolymerization of ethylene with 1,2-disubstituted polar internal olefin monomers.

Although the copolymerization process of 1,2-disubstituted polar internal olefin monomer and ethylene can be carried out through PO-Pd catalyst, the following problems still exist in this process: in the presence of more polar monomers, the catalytic activity of the catalyst Lower; this catalytic system cannot effectively copolymerize polar internal olefin monomers such as methyl oleate, which are used in large quantities in industry. This largely limits the choice of 1,2-disubstituted polar internal olefin monomers.

In order to apply polar internal olefin monomers such as methyl oleate to the preparation of functionalized polyolefins, and to further improve the utilization of polar monomers, they introduced a Ru-catalyzed ethylene decomposition process. In the presence of 1,2-disubstituted polar internal olefin monomer, Ru catalyst can effectively catalyze the ethylene decomposition process between the two. The resulting product is one same or two different terminal olefins, and then in the PO- Under the catalysis of Pd or PO-Pd * , the terminal olefin can be effectively copolymerized with ethylene to obtain a functional binary or terpolymer. The realization of this process is that two types of catalysts, Ru and Pd, are in one pot. By adjusting the polymerization temperature, the two catalytic steps (ethinylation at 30 C and copolymerization at 80 C) are carried out step by step and work in cooperation to achieve the entire process. The tandem process (Figure 3).

Figure 3. One-pot two-step tandem (ethyleneolysis and copolymerization) preparation of functionalized polyolefins based on 1,2-disubstituted polar internal olefin monomers.

This research result was published in the international authoritative journal Angew. Chem. Int. Ed. (2020, 59, 1206-1210) and was selected as a VIP article. The first author of the paper is Chen Min , a special associate researcher at the University of Science and Technology of China, and the corresponding author is Professor Chen Yuele of the University of Science and Technology of China. This work was supported by the National Natural Science Foundation of China.

Paper Information:

Min Chen, Changle Chen *

Direct and Tandem Routes for the Copolymerization of Ethylene with Polar Functionalized Internal Olefins.

http://doi.org/10.1002/anie.201913088

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