Issue 32/2012 - Styrene-butadiene Advances in the production of thermoplastic elastomers

Styrene-butadiene thermoplastic elastomer (SBC) is mainly made of styrene, butadiene or isoprene as monomer, alkyl lithium as initiator, and anionic solution polymerization
.
The current production methods mainly include three-step feeding method using single lithium initiator, two-step mixed feeding method, coupling method and two-step feeding method using double lithium initiator
.
In terms of technological progress, it is mainly reflected in the polarization modification of SBC, coupling agent technology, improvement of polymerization process and new product development
.

1.
Polarization modification

SBC has the advantages of high tensile strength, large surface friction coefficient, good low temperature resistance and excellent processing performance, but due to its small molecular polarity, its oil resistance and solvent resistance are poor, and its compatibility and adhesion with polar materials are also limited
.
At present, the chemical modification of SBC is mainly through the introduction of polar groups through unsaturated double bonds, such as epoxidation, grafting, sulfonation, etc
.

Sinopec Baling Petrochemical uses n-butyllithium as initiator, cyclohexane and tetrahydrofuran as mixed solvents, adds modified monomer after synthesizing active SBS, and introduces a small polar group at the end of SBS to prepare polar SBS (PSBS), the product has good compatibility with polar materials, and the peeling strength is about 50% higher than ordinary SBS, which can be directly used as a toughening modifier of nylon
.
Researchers from South China University of Technology prepared epoxySBS (ESBS)
by epoxidizing SBS by epoxidizing formic acid and hydrogen peroxide generated in situ.
The results show that the order of reactivity of the double bonds on the butadiene chain segment is: cis-1,4-structure> trans-1,4-structure> 1,2-structure
.
During the epoxidation reaction of SBS, a small amount of epoxy group will undergo ring-opening side reactions
.
When the ratio of C=C double bond, formic acid and hydrogen peroxide in SBS is 1:0.
5:0.
6, the reaction time is 2h, and the reaction temperature is 60°C, the epoxy mass fraction of ESBS is the highest, reaching 18.
1%.

Adding a small amount of polyethylene glycol to the system is conducive to the improvement of the
epoxy mass fraction of ESBS.

Epoxidation modification can not significantly improve the thermal stability of SBS/SIS under the condition of limited degree of epoxidation, while silicone modification can improve the thermal stability of the product, and at the same time can improve the polarity, adhesion and aging
resistance of SBS 。 Zhou Ting et al.
added the initiator azobisisobutyronitrile AIBN and the modifier vinyltriethoxysilane WD-20, WD-20: SBS=1.
2 (molar ratio), and reacted at 55~60 °C for about 4h, WD-20 and other organosilicon compounds and SBS grafted copolymers to obtain SBS silane grafted copolymers with obvious Si-C bond absorption peaks
.
The modified SBS thermal decomposition temperature can be extended up to 450 °C
.
Due to WD-20's good wetting ability to bond interfaces, the bond strength of the copolymer is also enhanced
.

Sinopec Baling Petrochemical researchers conducted a process study
on the grafting of maleic anhydride and acrylic acid in SBS.
The results show that under the process conditions of grafting reaction time of 56h and reaction temperature of 60~64°C, the grafting rate of SBS-g-MAH can reach 1%~2%.
Under the process conditions of grafting reaction time of 8~10h and reaction temperature of 62~64 °C, the grafting rate of SBS-g-AA can reach 9%~10%.


Researchers from Dalian Maritime University prepared an aminostyrene/butadiene/styrene ternary block polymer (SBS-N)
using n-butyllithium as the initiator of anionic polymerization and Schiff base as the capping agent for anionic polymerization.
The preparation of modified bitumen with SBS-N can significantly improve the performance of asphalt, reduce the degree of segregation, and thus improve the storage stability
.

2.
Coupling agent technology

Kraton Polymer Research has invented a process for coupling styrenic block copolymers, characterized by the use of 4-vinyl-1-cyclohexene diepoxy compound (VCHD) as a coupling agent
。 First, styrene or other vinyl aromatics undergo anionic polymerization to generate active styrene polymer blocks of the required molecular weight; Then, diolefins such as butadiene or isoprene undergo anionic polymerization to obtain the active end of the styrene polymer block; Then VCHD is added to the polymerization reaction mixture, the molar ratio of VCHD to polymer is 0.
5~0.
55, the temperature of the coupling reaction is 75~95 °C, and the coupling reaction time is not less than 30min
.

Jiang Yaoming et al.
of Sinopec Baling Petrochemical proposed a preparation method of star block copolymer of SBS or SIS, which is characterized in that the coupling agent is R1OOC-R2-COOR3 compounds (such as diphenyl terephthalate), where R2 is an alkyl or phenyl group of 1~8 carbons; R1 and R3 are alkyl or phenyl groups of 1~6
carbons.
Due to the use of halogen-free polyfunctional coupling agents, star copolymers do not affect the color of the product when agglomerating; The use of such coupling agents can make the star copolymer do not need to add alkyl lithium during hydrogenation; The coupling efficiency is more than 80%, and the coupling degree is more than
2.
5.

3.
Improvement of polymerization process

Sinopec Baling Petrochemical Zhang Hongxing et al.
provide a method to reduce the permanent deformation of linear styrene thermoplastic elastomers, with n-butyllithium or sec-butyllithium as initiator (when n-butyllithium is the initiator, a small amount of activator such as tetrahydrofuran should be added), cyclohexane or cyclohexane, hexane mixture, etc.
as solvent, a period of initiation temperature of 40~50 °C, the maximum temperature of the reaction shall not exceed 75 °C, and the reaction time is 20~50min; The initiation temperature of the second and third stages is 50~60 °C, the maximum temperature of the reaction shall not exceed 110 °C, and the reaction time is 20~50min; The concentration of reaction monomer is 10%~20% (weight percentage).

It is characterized by the completion of a styrenic monomer reaction, and the conjugated diolefin monomer and styrenic monomer are added to the reactor for the second and third stage reactions
.
The linear styrene thermoplastic elastomer prepared by this method has a permanent deformation of less than
25%.
In addition, Zhang Hongxing et al.
provide a method to terminate the polymerization reaction containing conjugated diolefins, in SBC synthesis, after the polymerization reaction is completed as required, the measured phenolic substances are added to the reaction kettle as a terminator, fully stirred, and the reaction is more than
1 min.
The products prepared by this method have low macromolecular content and good
product quality.

Sinopec Beijing Yanshan Petrochemical Company has developed "energy-saving SBS coalescing process technology" and applied it to the C line
of the SBS coalescing unit of the plant.
Using the combination of three-kettle differential pressure agglomeration and rubber particle water concentration technology, through the adjustment of temperature and pressure, the three condensing kettles have their own emphasis on solvent removal and energy saving, and at the same time, the concentration technology is used to concentrate the condensed particle water
.
The implementation of this project has significantly reduced the residual oil rate in the glue, reduced the emission of light hydrocarbons in post-treatment, solved the problem of high solvent content in the product, and the performance indicators of the finished product meet the quality standards, while the steam consumption is reduced, and the effect of energy saving and consumption reduction is remarkable
.
In addition, Baling Petrochemical developed a new technology of SBS three-kettle condensation, which extended the condensation time and improved the coagulation effect, and the cyclohexane and steam consumption of SBS production were greatly reduced
.

4.
New process of screw extrusion synthesis

Zheng Anna of East China University of Science and Technology et al.
invented a new type of styrenic block copolymer reaction extrusion polymerization method, including the following steps: styrene monomer, initiator, styrene/conjugated diolefin mixed monomer are sent to each section of the screw extruder for polymerization reaction, or styrene monomer, monofunctional organic alkali metal or alkaline earth metal initiator, styrene conjugated diolefin mixed monomer and coupling agent are sent to each section of the screw extruder for polymerization reaction to obtain styrenic block copolymer
。 The invention uses reactive extrusion technology, which shortens the entire production cycle to a few minutes, and basically has no solvent participation, no need for complex solvent separation and purification
.

5.
Development of new products

Kraton Polymers introduces Kraton A
, a new SEBS elastomer product.
Compared to conventional SEBS, the new resin has increased rigidity, improved processability, higher isotropy (longitudinal/transverse) during shrinkage, and stronger adhesion to a variety of engineering thermoplastics
overmolding.

BASF has developed a new injection grade SBS under the trade name Styrolux 3G33, which has better transparency, impact strength and stiffness than conventional SBS plastics, as well as faster melt flow, and better overall performance than PET, PVC or acrylic plastics
.
Recently, BASF launched a new SBS product under the brand name Styrolux 3G55, which has low production costs and good toughness, and can be blended with GPPS for extrusion and
thermoforming.

Baling Petrochemical Company has developed a special grade SBSYH-788 with linear structure, which has the advantages of large melting index, good transparency, high strength, good melt fluidity and good foaming, and can be used for the production of foamed soles, transparent injection molding products and toy products; High oil filling rate performance YS-803SBS products, belonging to star structure SBS, are mainly used in the production of high oil filling shoes granules, with high oil filling rate, fast oil absorption, stable performance after oil filling and so on; The new SBS grade TPEYH-168 for solvent-based adhesive has reached the international advanced level of similar new grades, and has good adhesion performance, cold flow resistance and processing performance
.
Baling Petrochemical Company also synthesized a new polystyrene block copolymer (SIBS) for asphalt modification through molecular design based on the principle of active anionic polymerization, and verified and further optimized
it on a 300-ton pilot plant.
User applications show that the product can effectively improve the ductility, high temperature storage stability and construction performance of modified asphalt, and the manufacturing cost is greatly reduced
compared with the traditional SBS796-H.

On the basis of the introduction of technology, PetroChina Dushanzi Petrochemical Company has developed the block ratio 40/60 linear adhesive SBS special material product T167
that meets the market demand.
At present, the company is conducting performance evaluation and market use tests
on the product.