Overview of the synthesis method of polycarbonate diol
In the past, the main soft segment raw materials of polyurethane produced on an industrial scale were divided into the following types: polyether type represented by polytetramethylene glycol; and adipate ester represented by Polyester polyol type; polylactone type represented by polycaprolactone; or polycarbonate type represented by polycarbonate diol. In contrast, polyurethane using polycarbonate type represented by polycarbonate diol is considered to be the best durability grade in terms of heat resistance and hydrolysis resistance, and is widely used as a durable film or artificial material for automobiles. Leather, (water-based) coatings, adhesives.
Synthesis method of polycarbonate diolSynthesis method
The synthesis of polycarbonate diol (PCDL) includes traditional phosgene method, transesterification method, cyclic carbonate ring-opening polymerization method and regulated polymerization method of carbon dioxide and epoxide, etc. The phosgene method uses phosgene and aliphatic diol as raw materials. The dichloroformate is first generated, and then reacts with the diol for chain extension to generate polycarbonate diol. However, this method has been basically eliminated because phosgene and hydrogen chloride cause serious corrosion to the equipment, generate a large amount of wastewater during neutralization treatment, and produce poor production conditions. The transesterification method uses diol and carbonate as raw materials to perform transesterification reaction to obtain polycarbonate diol (PCDL). Polycarbonate diols with various structures can be synthesized by adjusting the type of glycols. Among them, the transesterification reaction of small molecular polyol carbonates is currently the most mature method for synthesizing polycarbonate diols.
Although the raw materials for this method are easily available, the cost of synthesized PCDL is relatively high. Cyclic carbonate ring-opening polymerization method. During the ring-opening polymerization process, six-membered rings and cyclic carbonates larger than six-membered rings can form polymer polycarbonate diol. Five-membered ring cyclic carbonates undergo ring-opening polymerization. During polymerization, polycarbonate diols with very low molecular weights are produced. However, ring-opening polymerization has high industrial costs. Currently, there are relatively few studies using this method to prepare elastomers, coatings, and polyurethane (PU) adhesives. By regulating polymerization, polycarbonate diol can also be synthesized using CO2 and epoxide as raw materials, but this method requires high-pressure reaction equipment.
Application of synthesis method of polycarbonate diol
Polycarbonate diol is used as a raw material for the soft segments of polyurethane and thermoplastic elastomers used in artificial leather, synthetic leather, paints, coating agents, adhesives, etc., and is considered a polyether polyol. , the shortcomings of polyester polyol are excellent in heat resistance, weather resistance, hydrolysis resistance, etc., and are widely used as raw materials that impart high durability.
Synthetic method and preparation of polycarbonate diol
Method 1: A preparation method of polycarbonate diol. The method provided by the invention is: put a certain amount of glycol, urea and catalyst into a reactor, react under heating and stirring, and the glycol and urea undergo direct alcoholysis and polymerization reaction. After the reaction is completed, polycarbonate diol is obtained through simple separation. The preparation method has the characteristics of simple operation, high product yield, and easy industrial implementation of trifluoromethylbenzene boric acid. The details are as follows: Install an electric stirrer, thermometer and distillation device on a 250mL three-neck flask, add 118g 1,6-hexanediol and 1g dibutyltin oxide, heat to 160°C, and add 60g urea while stirring. Connect the tail ammonia absorption system, heat and stir the reaction, keep the temperature at 150-250°C, absorb the released ammonia, and react for 6 hours. 131g of light yellow viscous liquid was obtained. The hydroxyl value is 135.2mgKOH/g.
Method 2: A method for preparing polycarbonate diol. Polycarbonate diol is obtained through polymerization reaction of dimethyl carbonate and glycols, in which oxidized alkaline earth metal is used as a catalyst. The general reaction formula is as follows:
Specific steps include the following:
Step 1: Add the dimethyl carbonate, the glycols and the catalyst in a molar ratio of 1:1:0.0005-1:10:0.01 into a reactor whose internal atmosphere is nitrogen. ;
Step 2, perform initial heating of the reactor until the internal temperature of the reactor is 110-150°C, and control the internal temperature of the reactor.��Pressure is 0-5㎏/m2;
Step 3: After heating for 1-3 hours, start the reflux condensing methoxypyridine device to remove the preliminary waste methanol;
At this time, introduce all the evaporated gas to the reflux condenser, condense and reflux the unreacted dimethyl carbonate to participate in the reaction, and discharge the reaction by-product methanol vapor, which is also condensed and collected.
Step 4: When the distillation is not distilled, the reactor is heated twice until the temperature in the reactor is 200-250°C. After heating for 20-40 minutes, the waste methanol is completely removed. and unreacted raw materials;
Step 5, close the reflux device of the reflux condenser, heat the reactor three times until the internal temperature of the reactor is 200-250°C, and control the pressure in the reactor to 0.001 -0.05kg/m2, after heating for 80-120 minutes, remove the low molecular weight polycarbonate to obtain the final product polycarbonate diol which is a transparent liquid at room temperature.
