Issue 46/2015 - New developments in polyisoprene rubber production technology

Polyisoprene rubber (IR) is a synthetic rubber rubber made
by bulk polymerization or solution polymerization of isoprene monomer under the action of a catalyst.
According to the different structure of isoprene units, it can be divided into four isomers: high cis-1,4-polyisoprene rubber (referred to as isoprene rubber), trans-1,4-polyisoprene rubber, cis-3,4-polyisoprene rubber and 1,2-polyisoprene rubber
.
According to the initiation system, it can be divided into lithium-based, titanium and rare earth polyisoprene rubber
.

Lithium polyisoprene rubber

Lithium polyisoprene rubber is a kind of stereonormal elastomer
formed by the polymerization of isoprene monomer by anionic solution under the action of alkyl lithium initiator.
Its catalytic efficiency is high and the dosage is small; No gel and glue hanging phenomenon, high monomer conversion rate, can eliminate the monomer recovery process and remove catalyst process, the process is relatively simple
.
However, its cis-1,4- structural content is relatively low, only 91%~92%, and the comprehensive performance of the rubber is not as good as titanium isoamyl rubber
.
In addition, lithium-based catalysts are very sensitive to impurities, especially compounds containing oxygen, sulfur and nitrogen, and have more stringent
requirements for raw materials.

Chen Guozhong et al.
of Sinopec Chemical Division studied the effect
of diphenyldimethoxysilane (DDS) as an additive on the polymerization reaction with n-butyllithium as initiator and cyclohexane as solvent.
The experimental results show that DDS can improve the activity of the catalyst, adjust the content of the cis1,4-structure of the polymer, and the mass fraction of the cis-1,4-structure reaches more than
86%.

Wang Nini of Dalian Maritime University and others used n-butyllithium as initiator and isoprene as monomer to synthesize lithium isoprene rubber under a non-polar solvent system
.
The results show that solvent cyclohexane is superior to residual oil, and can synthesize cis-1,4-polymers with high structural content.
Under the cyclohexane solvent system, the lower initiation temperature, monomer content and high relative molecular mass are conducive to the formation of cis-1,4-structure, and the mass fraction of cis-1,4-structure of polymer is as high as 86.
9%.

Rare earth polyisoprene rubber

The catalyst for the synthesis of rare earth polyisoprene rubber consists of two important components, one is a rare earth salt and the other is a metal alkyl compound, usually using alkyl aluminum compounds
。 Isoprene rubber is synthesized by rare earth catalyst, which has high activity, less dosage, and easy uniform dispersion; The content of cis-1,4-isoprene of raw rubber is high, the relative molecular mass distribution is easy to adjust, the polymer gel content is low, and the ash content is low (mass fraction is less than 0.
3%).
The average molecular weight of raw rubber is large, the distribution is narrow, and it has high physical and mechanical properties and good processing properties; The initiator residue is harmless to the rubber performance, there is no need for water elution and ash removal, and the "three wastes" treatment amount is small; The catalyst is simple to prepare and use, the polymerization initiation speed is fast, the induction period is short, the anti-interference ability of impurities in the polymerization system is strong, and continuous polymerization
can be carried out in production.
Therefore, the synthesis of polyisoprene rubber catalyzed by rare earth has become a hot spot
in research and development.

Zhang Jie et al.
of Beijing Research Institute of Chemical Industry of Sinopec developed an isoamyl rubber and its continuous production method
.
The reaction materials containing isoprene, rare earth catalyst and solvent are continuously fed from the first adiabatic reactor in series to obtain the glue by polymerizing isoprene, and the glue is agglomerate, dehydrated and dried in turn; The feed temperature of the reaction material is less than 0 °C, and the rare earth catalyst contains neodymium carboxylate, alkyl aluminum and halide
with carbon atom number 7~14.
The preparation of isoprene rubber by this method can eliminate the temperature control system that regulates the polymerization temperature, reduce the production cost, and the mass content of cis-1,4-structure in isoprene rubber is greater than 98%.


Liu Naiqing of PetroChina Jilin Petrochemical Company and others have developed a wet agglomeration method
for rare earth isoamyl rubber.
The rubber hexane solution is preheated by steam, and is dispersed by the metering pump into the glue pretreatment device and circulating hot water, with a volume ratio of 1:4.
The pressure is 0.
3MPa, and the obtained 90~95 °C glue suspension is sprayed into the kettle by pulsating double-fluid mode through a nozzle with a thimble; the top of the kettle is stirred into a high-efficiency wide-blade axial paddle and a curved axial paddle with a speed of 300rpm; the bottom of the kettle is stirred for six-blade composite disc turbine stirring, with a speed of 400~500rpm; under the strong shear force of the bottom stirring and steam, it is quickly dispersed in the condensed hot water at 90~95 °C, and the hexane and monomer in the glue are instantly vaporized to form uniform rubber particles, and under the action of the kettle top stirring and spiral baffle, the rubber particles are all dispersed in hot water and stay for 20~30min ； The rubber particles are discharged tangentially at the mixing position at the bottom of the kettle in the direction of 30 degrees inclination, and hexane and monomer are discharged from the top of the kettle for condensation recovery
in the gas phase.

Li Yang of Dalian University of Technology and others developed a class of rare earth catalytic system star-branched polyisoprene and preparation method thereof
.
The polymer has an An-C structure, where A is a polyisoprene branched chain prepared by rare earth catalyst.
C is the astrobranching agent residue, and the astrobranching agent is epoxy; n is the degree of branching, and n is greater than or equal to 3
.
The weight-average molecular weight of star-branched polyisoprene is (10~100)×104, the weight-average molecular weight of polyisoprene branched chain A is (0.
5~20)×104, the mass percentage of cis-1,4-structure is 80%~98%, and the mass percentage of the sum of 3,4-structure and trans-1,4-structure content is 2%~20%.


Yang Liangliang et al.
of Beijing Research Institute of Chemical Industry of Sinopec developed an isoprene rubber and its continuous polymerization method
.
In the presence of an organic solvent and catalyst, isoprene monomers are polymerized in a continuous polymerization reaction unit comprising a plurality of tandem reactors
.
The method further comprises adding alkyl aluminum to the first reactor, and the molar ratio of the added alkyl aluminum to neodymium carboxylate in the first reactor is 1~15:1
.
This method can obtain isoprene rubber with the content (mol) of cis-1,4-structure in the structural unit greater than 98.
5%, and the single-pass conversion rate of continuous polymerization reaction is more than
95.
3%.

Trans-polyisoprene rubber

Ni Xufeng et al.
of Zhejiang University developed a catalyst
for the preparation of high trans polyisoprene by gas phase polymerization.
The components of the catalyst include a compound of the first component transition metal vanadium or titanium, a second component cocatalyst, a third component support, and a fourth component of nano-inorganic particles
.
Polyisoprene is prepared by this method to generate inorganic-organic alloys in the reactor containing the third and fourth components in situ, which can still have good anti-stick effect
when the content of nano-inorganic particles is as low as 0.
1wt%.

Zhang Chunyu, president of the Chinese Academy of Sciences, developed a preparation method
of low crystallinity and high trans-1,4-polyisoprene.
Isoprene, cocatalyst, main catalyst and comonomer were mixed sequentially, and prepolymerization and polymerization reactions were carried out to obtain low crystallinity and high trans-1,4-polyisoprene
.
This method effectively solves the problems of
polymer morphology control and polymer fluidity during bulk precipitation polymerization.

Jinlun Fu et al.
, Qingdao University of Science and Technology, used gas-solid phase method to chlorinate trans-1,4-polyisoprene (TPI) to obtain trans-1,4-polyisoprene (CTPI).

The results showed that with the increase of chlorine content, the crystallinity of CTPI decreased and the melting point decreased
.
As the size of TPI decreases and its relative molecular mass distribution narrows, chlorination is easier, the degree of chlorination is more uniform, and the more
crystallinity decreases.

other

Liaoning Heyun Synthetic Rubber Research Institute Co.
, Ltd.
Miao Lina et al.
developed a molecular weight distribution adjustment method
for 3,4-polyisoprene rubber.
Under the protection of nitrogen, isoprene monomer, organic solvent, and then catalyst are added, and then polymerization reaction at 0~70 °C for 1~6h, and then 2,6-di-tert-butyl-4-p-cresol solution is added to the polymerization system, and the polymerization glue is washed and dried to obtain polyisoprene rubber
with molecular weight distribution index Mw/Mn of 1.
26~3.
89.
This method has the advantages
of gel-free products, simple operation, low cost, and easy implementation.

Zhang Chunyu, president of the Chun Institute of Applied Chemistry, Chinese Academy of Sciences, etc.
mixed isoprene, diisobutyl (2,6-di-tert-butylphenol) aluminum and the main catalyst for prepolymerization reaction, and after 0.
5~5h, butadiene was added for polymerization reaction to obtain polyisoprene rubber alloy
with core-shell structure 。 The high trans 1,4-structure was prepared by segmented polymerization method, which solved the fluidity problem of polyisoprene during processing while ensuring the high anti 1,4- content of polyisoprene, and obtained high-performance polyisoprene alloy, which can fundamentally solve the polymer morphology control in bulk precipitation polymerization and avoid the occurrence
of polymer particle bonding in the process of modifying trans polyisoprene with isoprene and butadiene.

Wu Jiaming of Shanghai University of Engineering Science and others developed a preparation method
for vulcanized polyisoprene rubber at room temperature.
This method not only realizes the vulcanization of polyisoprene rubber at room temperature, but also has excellent mechanical properties and solves the problem
that polyisoprene rubber is not easy to form and process.

He Aihua of Qingdao University of Science and Technology et al.
developed a high molecular weight polyisoprene rubber
containing 3,4-structure, cis-1,4-structure and trans-1,4-structure.
The prepared product not only has good wet slip resistance, but also has the characteristics of low heat generation; The catalyst system used is insensitive to water, oxygen, carbon dioxide, etc.
, and the experimental operating conditions are mild, especially suitable for high-performance tires and other rubber products
.

Development priorities

Accelerate the research and development of catalytic technology, further improve the content of cis-1,4 structure, so that polyisoprene rubber products have high chain normalization (high cis content and sequence distribution), controllable relative molecular mass (narrow relative molecular mass distribution) and polarized polymer chain (end modification, etc.
) characteristics in structure, reduce viscosity, and improve the comprehensive properties
of rubber.

Through modification and other technologies, develop high-end products and improve the technical level
of China's tire and other industries.
It mainly includes improving the performance of vulcanized rubber of polyisoprene rubber raw rubber and rubber mixtures in view of the difference with natural rubber; Chemical modification by halogenation, hydrogenation, cyclization, etc.
, to expand the field of application
.