In 2006, the prices of low molecular weight polyisobutylene soared and often faced shortages, followed by a similar trend in 2007 for medium molecular weight polyisobutylene, which also experienced price hikes and supply constraints. This situation confirmed the prediction made by the China Petroleum and Chemical Industry Association that domestic demand for polyisobutylene has been steadily increasing, driven largely by the growing need for insulating glass sealants and chewing gum bases.
With the widespread adoption of plastic steel windows and the rapid penetration of hollow glass into residential areas, the market potential for polyisobutylene in China is vast. In the field of insulating glass sealants, polyisobutylene enhances flexibility and permeability. The current sealing structures in the market are typically single or double seals. A single seal involves using a gasket, while a double seal employs two types of adhesives: medium molecular weight polyisobutylene as the first sealant and high-strength polysulfide rubber or silicone rubber as the second. Regardless of the structure, medium molecular weight polyisobutylene plays a critical role due to its excellent water resistance and sealing performance. It generally constitutes about 20% of the sealant strip, and up to 40% or more in the first layer of a double-seal system.
Currently, the main suppliers of medium molecular weight polyisobutylene in China are products from BASF (Germany), ENEOS (Japan), Jihua, and Shunda. As environmental regulations become stricter, the demand for this material is expected to grow further.
Polyisobutylene, when blended with paraffin wax and resin, improves the quality of chewing gum, making it softer, more stable, and maintaining good hydrophobic properties and film-forming ability. Food-grade medium molecular weight polyisobutylene used in chewing gum bases must be produced using a boron trifluoride catalyst system. This method ensures clarity, high purity, and the ability to meet medical and food-grade standards. However, some domestic manufacturers use an aluminum trichloride catalyst system, resulting in lower purity, wider molecular weight distribution, and poor appearance, limiting their applications. Therefore, most of the chewing gum base polyisobutylene currently used in China is imported, mainly from BASF and ENEOS.
Additionally, polyisobutylene can be mixed with various adhesives, including pressure-sensitive adhesives, to create food-grade adhesives. It can also be combined with paraffins and polymers to serve as release agents for packaging films and food packaging materials, as well as for hot melt adhesives.
Domestic producers of medium molecular weight polyisobutylene include the additive plant of Lanzhou Refining and Petrochemical General Plant, the chemical fiber plant of Daqing Petrochemical Plant, the Fine Chemicals Plant of Jilin Petrochemical Company, and Hangzhou Shunda Group Polymer Materials Co., Ltd. However, many of these facilities have either ceased operations or are underutilized. Only Hangzhou Shunda continues production, having transformed its low-molecular-weight facility into a medium-molecular-weight one, claiming a capacity of 10,000 tons per year, though industry sources suggest it may only reach 6,000 tons.
The production process for medium molecular weight polyisobutylene, developed jointly by Hangzhou Shunda and the National Key Polymerization Laboratory, uses boron trifluoride catalysts and has won a national invention patent. It features a simple process, high-quality output, low cost, and safe operation. Despite this, most products still rely on the aluminum trichloride system. Meanwhile, Jilin Petrochemical’s new 2,000-ton-per-year plant, set to start in February 2008, will use the boron trifluoride system.
The successful development and industrial application of the boron trifluoride catalyst system will enhance product quality, expand application areas, and improve international competitiveness, gradually reducing reliance on imports. Promoting the production of medium molecular weight polyisobutylene not only meets domestic demand but also upgrades local products and improves the utilization of MTBE and C4 resources, holding significant economic and strategic value.
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