Background and overview[1][2]
Hexamethylphosphoric acid triamide is a high boiling point, highly polar organic solvent with excellent performance. It is also a very valuable chemical reaction medium with catalytic properties. It has important applications in the polymer synthesis industry. .
Since the 1990s, there has been considerable scale production abroad and it has been widely used. But so far only a few factories in the country produce it. Because of its backward synthesis method, low yield and high cost, some studies have compared domestic and foreign methods of synthesizing hexamethylphosphoric acid triamide and studied a new process to reduce the production cost of hexamethylphosphoric acid triamide. , eliminate or reduce pollution in production and improve product quality. Because the synthetic raw materials and processes involve toxic and volatile phosphorus oxychloride, amines, etc., the first attempt was made to use micro-chemical synthesis methods to study this synthesis process, and preliminary results have been obtained.
Apply[2]
Hexamethylphosphoric acid triamide is currently mainly used in polymer materials in my country as a solvent for the condensation reaction of polyphenylene sulfide (PPS) and as a modifier for MC-nylon. In addition to greatly improving the weather resistance and photo-oxidation resistance of the resin, its other main feature is its excellent compatibility with most resins, that is, hexamethylphosphoryltriamide molecules can combine into the molecular chain of the polymer, thus breaking the bonding points on the original polymer chain structure and selectively decomposing the polymer at these points.
1) As an excellent selective inert solvent for solution polymerization
High melting point resins developed in recent years, such as polyhydrazides and polyoxydiazole, can withstand 45 0 ℃ high temperatures and can be processed into various mechanical components, fibers or films. . Hexamethylphosphoric acid triamide is one of the best solvents for this type of resin. It can be used to complete the polycondensation reaction at a lower temperature. The so-called inertness only means that hexamethylphosphoric acid triamide is the acceptor of H C I in the reaction for reactants and products, so it can move the reaction to the right.
2) Used as anti-photograding agent, weathering agent, modifier or synergist for thermoplastics
The photoaging phenomenon of thermoplastic resins, especially polymers or copolymers of α-olefins such as propylene and styrene, is much more serious than that of thermosetting resins. Polypropylene or polyethylene film or fiber will become brittle after being exposed to the sun for 3-6 months outdoors. If 2% hexamethylphosphoric acid triamide and 1% 2-hydroxy-4, 4 ‘-Dimethoxybenzophenone or benzophenone-type ultraviolet absorber with similar structure (UV-9) , the film still maintains an elongation at break of 103% after being subjected to an aging machine for 70 hours, while the blank control sample without additives is only 7%.
3) Used as an efficient weathering agent for polyethylene and other chlorine-containing resin products or coatings
The soft polyvinyl chloride test piece stabilized with hexamethylphosphoric acid triamide can withstand outdoor exposure to the sun, rain, wind, frost, ice and snow for many years without deterioration. It can still maintain good flexibility, mechanical strength and The bending resistance test was conducted on a roof in the United States and was exposed to the sun for seven years without deterioration. Hexamethylphosphoric acid triamide is suitable for use in calendered films, extruded or compression molded products, plastisols and organosols. Hexamethylphosphoric acid triamide has poor high-temperature stability, which will cause the polyvinyl chloride to be heat-sensitive and slightly yellowish-brown. However, this shortcoming can be synergized by using organic tin or epoxy stabilizers with good heat resistance. to overcome it.
4) Hexamethylphosphoric acid triamide as a catalyst or cocatalyst for the polymerization of α-olefins and other monomers
The third component of the catalyst for isotactic polymerization of α-olefins, etc., can effectively improve propylene, butylene, styrene, 1,3-pentadiene, α-methyl It can also increase the degree of isotactic polymerization of monoolefins or diolefins such as styrene, thus improving the bonding properties, softening point, thermal stability and rigidity of these polymers. When polymerizing styrene, using hexamethylphosphoric triamide as a cocatalyst and polyethyl vinyl ether as the dispersant, a uniformly dispersed high molecular weight polymer can be obtained, and the product is easy to separate.
When using a catalytic system of metallic sodium and hexamethylphosphoric acid triamide in tetrahydropyran and hexamethylphosphoric acid triamide, polymerization is performed at 0-5 ℃ , can obtain better poly α-methylstyrene. In the polymerization of butadiene, hexamethylphosphoric acid triamide can be used as a cocatalyst to synthesize low molecular weight polybutadiene oil, or solid polybutadiene with uniform molecular weight distribution can be synthesized. Polyurethane uses hexamethylphosphoric acid triamide as a co-catalyst to obtain industrial synthetic fibers with good elasticity. France uses hexamethylphosphoric acid triamide as the catalyst component and copolymerizes ethylene and propylene to synthesize ethylene-propylene rubber with improved elasticity and oil resistance. Propylene is multi-step copolymerized with other monoolefins, butene, hexene, etc. using hexamethylphosphoric acid triamide as a catalyst to obtain a block copolymer resin with excellent low-temperature properties.
Preparation [1, 3]
Method 1: The synthesis reaction formula of hexamethylphosphoric acid triamide is:
It can be seen from the reaction formula that half of dimethylamine is consumed to generate dimethylamine hydrochloride. In order to save dimethylamine, ammonia gas can be introduced into the reaction mixture in the middle stage of the reaction to Ammonia replaces dimethylamine in dimethylamine hydrochloride, thus saving nearly 50% of dimethylamine. The reaction formula is:
The by-product ammonium chloride is easily separated from the crude product. In a 2000mL four-neck bottle with electric stirring, first add 1mL of toluene solution, then add 200g of phosphorus oxychloride at one time, and meter in dimethylamine while stirring continuously. When the reaction proceeds to neutrality, ammonia gas is introduced to the end point of the reaction. After cooling at 60°C for 1 hour, the by-product ammonium chloride was obtained by filtration. The filtrate was distilled to obtain 195.2g of HPT product with a purity of over 98%, with a yield of 82%. The new process of synthesizing HPT using toluene as the solvent requires mild conditions. The key is to ensure that the phthalocyanine pigment raw materials and the system are dry and free of water. It is also important to accurately control the addition of ammonia in the middle of the reaction. If dimethylamine is insufficient and ammonia is added prematurely, it will affect the progress of the amidation reaction and be detrimental to the generation of HPT.
Method 2: Apply micro-chemical synthesis method to synthesize hexamethylphosphoric acid triamide: install micro-synthesis reaction equipment. Add 5 mL of phosphorus oxychloride to the two-neck flask, add a certain amount of dimethylamine that has been pre-dissolved in hexamethonium phosphorus according to stoichiometry, and slowly heat using an oil bath placed on a magnetic heating stirrer. When the reaction proceeds to a certain extent, the temperature is raised to 90°C. After a few hours, the synthesis reaction is completed. The synthesis principle is shown in the reaction equation below.
Main reference materials
[1] Microchemical synthesis of hexamethylphosphoric acid triamide
[2] Application of hexamethylphosphoric acid triamide
[3] New synthesis method of hexamethylphosphoric acid triamide
