Intelligent design of synthetic rubber II

(1) Performance

Low cis polybutadiene has distinct characteristics compared to polybutadiene using other catalytic systems. First of all, in the molecular arrangement, its cis and trans structures are irregularly distributed, so that the cold resistance is better and the low temperature flexibility is more excellent. Second, the molecular weight distribution of low cis polybutadiene is narrower than that of ordinary butadiene rubber, and the processability is worse than the latter. Third, its color is lighter than ordinary butadiene rubber, with higher transparency and lower gel content. Therefore, it has good resilience, compression set resistance and wear resistance, and its aging resistance is superior to that of natural rubber.

(2) Polymerization process

With an alkyl lithium as an initiator, butadiene is anionically polymerized in a non-polar solvent to obtain a low cis polybutadiene. According to the ratio of microstructure, the butadiene chain links in the molecular chain are: cis-1, 4 structure 35%~38%, trans-1, 4 structure 50%~55%; in addition, there are vinyl 8% to 12%. The polymerization reaction is chain-type, including three stages of chain initiation, chain growth and chain termination. The characteristic of the polymerization is that the molecular weight always increases with the increase of the conversion rate, which is obviously different from the free radical polymerization.

(3) Variety specifications

Mainly divided into “rubber use” and “plastic modification” for users to choose. Generally, the rubber type is mainly Mooney viscosity 35 and 45, and when used for plastic modification, the Mooney viscosity is 55. In order to meet the needs of high impact resistance and high styrene modification, a variety of Mooney viscosity >55 was added, which expanded its application in plastic modification.

(4) Application

Since the 1970s, the development of low-cis polybutadiene has been slow but relatively stable, with annual growth rates ranging from 2% to 3%. One of the main application areas is the tread rubber of heavy-duty tires, which is designed to maintain good mechanical properties at low temperatures. Although its performance in this respect exceeds that of natural rubber and high-cis polybutadiene, it takes a long time to completely replace the original rubber as a new rubber, and it is not possible to complete it overnight.

It now appears that the field of faster application development is not a traditional vulcanizate product, but rather a modification of resins such as polystyrene (PS) and ABS. The amount of low cis polybutadiene used in this area in the United States has increased year by year, ranking first among various modified materials (about 65% to 70%). On the other hand, this consumption is equivalent to 30% of the total consumption of polybutadiene (including tires). The application of polybutadiene in plastic modification continues to expand, and its importance is obvious.