Polyolefin is the main part of the heat shrinkable tube, because of the molecular structure, olefin monomer is not as easy to occur free radical polymerization reaction as the vinyl monomer with polar substitution group, so the Polyolefin industrialization time than polystyrene, polyvinyl chloride, poly methyl methacrylate, polybutadiene and other polymers to be late. It was only in the 30 's that it was discovered that ethylene polymers could be obtained under high temperature and pressure (greater than 100MPa). Later, by the 1950s, after the development of catalysts such as Ziegler-natta catalysts and Phillips, polyethylene and polypropylene have rapidly become industrialized large varieties of products.
After about half a century of development, the initial z-n catalyst has developed into today's highly efficient and high-performance catalysts, in the the 1980s and 90 's, and successively developed metallocene catalysts and post-transition metal catalysts, forming a common development of a variety of catalysts in today's pattern. Polyolefin resins are also transformed from general-purpose materials to functional materials. Throughout the history of Polyolefins, the development of polyolefin materials is inseparable from the progress of its catalysts, and the successful development of each new type of catalyst system will bring new polymerization processes and new polyolefin products, so that polyolefins can be used in a wider field.
Over the past 50 years, there are more than 20 kinds of production of polyolefin technology routes, all kinds of technology according to the type of polymerization, polyethylene can be divided into high-pressure method, gas phase method, solution method, slurry method (also known as solvent method); Polypropylene can be divided into main body method, body gas phase combination method, gas phase process. The initial production process includes a complex post-processing process in the process, after the 1980s, with the successful development and application of high-activity, high-performance catalysts, the post-treatment process was canceled in the production process. In the 90 's, the new technology of polyolefin industry represented by the condensed gas fluidized bed process of UCC and Exxon Company and the supercritical slurry process of Nordic Borealis Co., Ltd., which greatly promoted the improvement of existing production capacity and the diversification of resin properties. Over the past 50 years, the Polyolefin field has developed greatly, and has made many significant technical achievements.