Polymerization is the process of converting low molecular weight monomers into high molecular weight polymers, which can be divided into chain polymerization and step polymerization. Thanks to the development of polymerization reaction, many materials with excellent properties were synthesized, which greatly improve people's living standard and promote the progress of technology. Many types of polymerization reagents are used in polymerization reactions, which play important roles in the polymerization reaction, such as increasing the rate of reaction, increasing the specificity of reaction, and the others.
- Polyethylene products: With the advantages of good insulation, low temperature resistance, and chemical stability, polyethylene products are widely used in pipe, film, hollow products, wire, cable, and the others. According to the density, polyethylene products are mainly divided into high density polyethylene (HDPE), medium density polyethylene (MDPE), low density polyethylene (LDPE), and linear low density polyethylene (LLDPE). Polyethylene products are generally obtained by copolymerization of α-olefin and ethylene, and catalyst is the core of polyethylene production process.
- Acrylic resin: Acrylic resin has the advantages of light color, color retention, weather resistance, corrosion resistance, pollution resistance, and the others. It is widely used in the furniture, buildings, leather products, daily necessities, paper printing and dyeing, wood processing, plastic synthesis, and other aspects. The use of crosslinking agent is an effective means to modify the properties of acrylic resin, which can greatly improve the properties of water resistance and solvent resistance and reduce the sensitivity to temperature.
- The others: Polymerization reagents are also used by synthesizing other polymerization products, including ethylene propylene rubber, ABS resin, polypropylene products and the others.
- Initiators: Initiators can be divided into peroxide initiators, azo initiators, disulfide initiators, redox initiators, bifunctional initiators, multifunctional initiators, macromolecular initiators, and the others. Azo initiators are widely used in aqueous solution polymerization and emulsion polymerization. Bifunctional initiator refers to a compound containing two active groups in the same initiator molecule, while multifunctional initiator contains more than three active groups in one initiator molecule. Macromolecular initiators are macromolecular compounds with free radicals on the molecular chain.
Figure 1. An example of macromolecular initiator applied in polymerization.
- Catalysts: Catalysts play important roles in polymerization reactions, such as speeding up the reaction rate, reducing the conditions required for the reaction, and the others. Catalysts mainly include Ziegler-Natta catalyst, chromium-based catalyst, metallocene catalyst, non-metallocene catalyst, composite catalyst, etc. Chromium-based catalysts are mainly divided into organic chromium and inorganic chromium catalysts. Metallocene catalyst is a catalytic system composed of metallocene compounds and methyl aluminoxane. Non-metallocene catalysts include pre-metallocene transition metal catalysts and post-metallocene transition metal catalysts. The advantage of non-metallocene catalysts is that the steric hindrance can be changed by changing the ligand structure, and then the performance state of polymerization products can be regulated.
Figure 2. An example of Ziegler-Natta catalyst applied in polymerization.
- The others: In addition to the above mentioned ones, polymerization reagents also include crosslinking agent, surfactants, and chain transfer agents.
- S. Mu, J. Guo, C. Yu, et al. Synthesis and Applications of ATRP Macromolecular Initiator[J]. Progress in Chemistry, 2015, -281X(ISSN):539-549.
- Nuyken O, Pask S. Ring-Opening Polymerization—An Introductory Review[J]. Polymers, 2013, 5(2):361-403.