Solution polymerization generally refers to a reaction process in which a monomer is dissolved in a solvent and an initiator is added to carry out polymerization. The advantages of the method include easy heat dissipation, easy control of the reaction process, low viscosity of the solution, easy purification, and easy molecular weight adjustment. The disadvantage is that the concentration of the monomer is reduced after using the solvent.
In addition, chain transfer is also apt to occur, the average molecular weight is low, the solvent is difficult to remove, and the solvent cost is relatively higher than the emulsion polymerization. If the obtained polymer (synthetic rubber) is insoluble in a solvent, it will precipitate as the reaction progresses, and it is called “precipitation polymerization J. The polymer obtained has a high molecular weight and good uniformity.
However, this ideal situation does not exist in rubber synthesis. It is feasible to precipitate the precipitate by pouring the polymer into a solvent which cannot dissolve the monomer, and the resulting precipitate is subjected to a series of post-treatments such as drying and degassing to obtain a synthetic rubber. Take the solution of styrene-butadiene rubber (SSBR) as an example, and briefly introduce the following.
Solution polymerization generally employs an anion polymerization system using an alkyl lithium as an initiator. The host material (monomer) is made of butadiene and styrene in a content of 99% to 99.5%, and the solvent is cyclohexane or hexane.
The procedure for each step is as follows.
1 The polymerization is carried out in a single-pot batch polymerization or a multi-tank continuous polymerization. The basic process conditions are: polymerization temperature 50~100 ° C, time 20 min, polymerization period 60 min, the coupling agent used is silicon tetrachloride, and the monomer conversion rate is 100%.
2 De-liquid flashing When the temperature reaches 90~100 °C, add anti-aging agent, concentrate the glue to 20%, and carry out flash desolvation.
3 Blending The flashed concentrated glue liquid is transferred to the buffer tank, and the blending of different batches is carried out to achieve the technical performance after blending.
A double or three-pot (50 m3 per tank volume) was used for agglomeration. The stirrer in the agglomerator is 45. Folding paddles, the glue ratio is required to reach 6:1. If a double kettle is used, the temperature of the No. 1 kettle is maintained at 85 to 88 ° C, and the No. 2 kettle is maintained at 96 to 105 ° C.
4 After treatment, the agglomerated material still contains 50% solvent after separation, and then the solvent is removed by a squeeze type liquid separator. The temperature of the machine head is required to reach 160~180 °C, and then transported and dried by hot air. Finally, the total amount of volatiles is reduced to less than 1%.