Preparation of Butyl Rubber by Cationic Solution Polymerization
The process of cationic polymerization generally includes the refining and preparation of monomers and other components, the preparation of initiators, the polymerization process, the separation of unreacted monomers and solvents, recycling, and post-processing of polymerization products.
The influencing factors are usually affected by solvent and temperature.
The following table lists the solvents and related parameters for cationic polymerization.
| Solvents and related parameters for cationic polymerization | ||||
| Solvent | Melting point/℃ | Boiling point/℃ | Relative density | Dielectric constant |
| Ethylene | -181 | -103.7 | ||
| Ethane | -183.3 | -88.6 | ||
| propane | -189.9 | -42.1 | 0.585（-45℃） | 1.61（0℃） |
| n-butane | -138.9 | -0.5 | 0.58 | 1.76（20℃） |
| n-Hexane | -95 | 69 | 0.66 | 1.890（20℃） |
| cyclohexane | 6.6 | 80.7 | 0.779 | 2.023（20℃） |
| benzene | 5.5 | 80.1 | 0.879 | 2.248（20℃） |
| Toluene | -95 | 110.6 | 0.867 | 2.379（25℃） |
| Methyl chloride | -97.7 | -24.2 | 0.916 | 12.6（-20℃） |
| Ethyl chloride | -136.4 | 12.3 | 0.898 | 16.5（-72℃） |
| Dichloromethane | -95.5 | 40 | 1.327 | 9.08（20℃） |
| Chloroform | -63.5 | 61.7 | 1.483 | 4.806（20℃） |
| Tetrachloromethane | -23 | 76.5 | 1.594 | 2.238（20℃） |
| 1,2-Dichloroethane | -35.4 | 83.5 | 1.235 | 10.65（20℃） |
| chlorobenzene | -45.6 | 132 | 1.106 | 5.708（20℃） |
| o-Dichlorobenzene | -17 | 180.5 | 1.305 | 9.93（25℃） |
| m-Dichlorobenzene | -24.7 | 173 | 1.288 | 5.04（25℃） |
| Nitromethane | -17 | 100.8 | 1.137 | 35.9（20℃） |
| Nitroethane | -50 | 115 | 1.045 | 28.06（30℃） |
| Nitrobenzene | 5.7 | 210.8 | 1.204 | 34.82（25℃） |
| carbon dioxide | ‘-56.5（5am） | -78.5 | 1.6（20℃，50atm） | |
| carbon disulfide | -110.8 | 46.3 | 1.263 | 2.641(20℃) |
| sulfur dioxide | -72.7 | -10 | 17.6(-20℃) | |
The cationic growth active chain is very active and is prone to chain transfer to monomers and solvents. When the polymerization temperature is high, the molecular weight of the product will decrease a lot. In order to synthesize high molecular weight polymers, it must be carried out at a very low temperature.
The total activation energy of cationic polymerization is in the range of -21~42kJ/mol, which is relatively small. When the activation energy is complex, the chain growth rate increases with decreasing temperature, which is a phenomenon unique to cationic polymerization.
Cations can only polymerize at lower temperatures. For example, the average chain length of the polymer obtained by the cationic polymerization of isobutylene has a turning point near -100℃. This is because above -100℃, the chain transfer is mainly to the solvent, and below -100℃, the chain transfer is mainly to the monomer. Industrial production of butyl rubber Select the reaction temperature to be around -100℃.
Butyl rubber is a random polymer obtained by cationic polymerization of isobutylene and isoprene under the action of a cationic initiator. The macromolecular chain of butyl rubber has a linear structure with basically no branches. On the macromolecular chain, isobutylene is mainly connected head to tail, isoprene is mainly a trans-1,4-structure, and the aggregated structure is non-branched. Take shape. Under normal circumstances, the glass temperature of amorphous butyl rubber is about -70℃, and it can crystallize under stretching. The following table shows the air tightness of several common rubbers.
| Air tightness of several commonly used rubbers | |||||
| Rubber variety | Air | oxygen | Nitrogen | carbon dioxide | hydrogen |
| natural rubber | 100 | 100 | 100 | 100 | 100 |
| Styrene-butadiene rubber | 65 | 73 | 60 | 72 | 84 |
| Neoprene | 30 | 17 | 24 | 25 | 27 |
| Butyl rubber | 13 | 6 | 11 | 14 | 15 |
Compared with other highly unsaturated rubbers, butyl rubber's ozone resistance is about 10 times higher than that of natural rubber, styrene-butadiene rubber, etc. Its resistance to heat, sunlight and oxygen is better than other general-purpose rubbers. It has better high temperature > 100℃, elasticity and higher heat resistance. (About 150℃). Good electrical insulation, better than ordinary rubber.
Butyl rubber also has shortcomings. Due to the small amount of isoprene, the vulcanization speed is reduced, which hinders the co-vulcanization of butyl rubber and highly unsaturated rubber commonly used in tires. Butyl rubber has poor adhesion to other rubbers, self-adhesiveness and It has poor mutual adhesion and is not easily compatible with other rubbers. Poor resilience and high calorific value. The molecular weight of vulcanized rubber of butyl rubber will decrease after thermal aging, so it is a thermally degradable polymer. The halides of butyl rubber are chlorobutyl rubber and bromobutyl rubber. The compatibility, self-adhesion and mutual adhesion of its halides with other polymers are also better than those of butyl rubber. These two halogenated Butyl rubber is currently a common material for tire inner liners and pharmaceutical bottle stoppers.
The copolymerization reaction of butyl rubber is as follows:
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There are two polymerization methods for butyl rubber production: solution polymerization and slurry polymerization. We will discuss this in the next stage.
