Production method of SAN resin through polymerization in two serially-connected kettles

Abstract

The invention relates to a production method of SAN resin through polymerization in two serially-connected kettles. 34 to 52 parts by weight of acrylonitrile and 48 to 66 parts by weight of styrene are introduced into the first polymerization kettle, and 32 to 50 parts by weight of acrylonitrile and 50 to 68 parts by weight of styrene are introduced into the second polymerization kettle. The stay time of materials in the first kettle accounts for 0.1 to 30% of the total stay time, and the stay time of materials in the second kettle accounts for 70 to 99.1% of the total stay time. The reaction mixture in the first kettle is mixed with fresh materials, which are to be introduced into the second polymerization kettle, outer circulation materials of the second polymerization kettle, monomer condensed liquid in the kettle top, and volatile condensed liquid in a static mixer, and then the mixture is transferred to the second polymerization kettle. The mixture is polymerized at a temperature of 140 to 160 DEG C so as to obtain SAN copolymer with a high acrylonitrile content. The acrylonitrile content of the obtained SAN resin is not less than 32%, the fusion index is less than 6g / 10min, and the molecular weight distribution index (Mw / Mn) is less than 2.

Description

technical field [0001] The invention relates to the copolymerization technology of styrene and acrylonitrile in the field of petrochemical industry, especially the copolymerization technology under high acrylonitrile content. More specifically, it adopts the method of two-tank series copolymerization, Background technique [0002] SAN resin is a copolymer of styrene and acrylonitrile. It has good transparency, mechanical properties, chemical resistance and permeability resistance. It is mainly used in transparent structural materials or as a blending component of polymer alloys. [0003] The SAN copolymer is a quite complex mixture in terms of chemical composition, and the molecular weight size and distribution, the acrylonitrile content in the copolymer and other indicators have a great influence on the performance of the SAN resin. With the increase of acrylonitrile content in SAN resin, the mechanical properties, solvent resistance and temperature resistance of the resin...

AI Technical Summary

Problems solved by technology

[0008] However, in engineering practice, for the characteristics of the conventional heat-initiated continuous bulk polymerization method, if the existing single-pot process is used to prepare SAN products with high nitrile content, due to the increase of the proportion of acrylonitrile in the reaction feed, this will face The following problems: (1) The viscosity of the polymerization system of SAN resin with high nitrile content increases. At the same time, the increase of acrylonitrile content, because acrylonitrile is a polar group, and ethylbenzene is usually used as a solvent in the polymerization process, ethylbenzene It is a non-polar solvent, so with the increase of acrylonitrile content in SAN, ethylbenzene has gradually become a poor solvent for SAN resin. The combination of these will lead to a sharp increase in the viscosity of the reaction system, which will bring about difficulties in removing heat and mixing. The system appears uneven; (2) The increase of acrylonitrile content in the reaction feed increases the probability of acrylonitrile homopolymer or ultra-high content acrylonitrile copolymer in the reactor under the condition of longer residence time , leading to a wider distribution, which will greatly deteriorate the mechanical properties and color of the material; (3) The increase in the content of acrylonitrile in the reaction system will increase the amount of acrylonitrile monomer evaporated in the polymerization reactor, which will require the reactor to feed There is a higher content of acrylonitrile in the monomer composition, which will further exacerbate the aforementioned two problems and form a vicious circle. At the same time, the content of acrylonitrile in the evaporated gas phase is higher, which increases the generation of acrylonitrile in the condenser. Chances of homopolymers or copolymers with high acrylonitrile content, these components are insoluble gel-like polymers with very low thermal stability, causing red and black spots on the molded article, spoiling the appearance of the article

According to experiments, high nitrile SAN resin is prepared in the existing equipment, and the tensile properties, impact strength and yellow index of the obtained product are difficult to achieve satisfactory results

Therefore, it is difficult to prepare SAN resin with high nitrile content and narrow distribution. It is necessary to explore a new polymerization process to solve the problems caused by long residence time, high viscosity of the system, and evaporation and heat removal of acrylonitrile.

According to the results of literature research, there are few literature reports on the preparation method of SAN resin with high nitrile content. In Chinese patent CN85106459A, a process for continuous bulk polymerization of styrene and acrylonitrile is disclosed. Acrylonitrile in the copolymer of its embodiment 5 The content is 33%, which belongs to high nitrile content SAN resin, but its distribution and yellow index are not specified

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