What are the production methods and steps for polypropylene glycol PPG?
Polypropylene glycol PPG is miscible with epoxy resin and has low viscosity at room temperature. It is a good diluent for epoxy resin, with high boiling point, non volatile, no toxic side effects, and safe operation; It participates in the curing reaction of epoxy resin. The molecular structure has a flexible fat long chain, which can rotate freely and is elastic. Adding it to the formulation of epoxy resin can greatly improve its impact strength and cold and hot shock resistance, and improve the embrittlement defects of epoxy cured products. Generally, a one-step synthesis method is used for the production of polypropylene glycol PPG, but this method is difficult to control the reaction conditions during the synthesis process of polypropylene glycol PPG. There is also a solid alkali method, which is difficult to operate, difficult to control temperature, and has many side reactions. Relatively speaking, using a two-step synthesis method, especially when reacting with solvents, is relatively simple and the temperature is easy to control. Below is a detailed introduction to these two production methods of polypropylene glycol PPG. First, let me introduce the method of synthesizing polypropylene glycol PPG through a mixed catalyst. The steps are as follows:
(1) Ring opening reaction: Weigh propylene glycol and epichlorohydrin in a mass ratio of 1:2.4, and then weigh 300-400 parts of toluene per mole of alcohol. Mix propylene glycol and toluene with the ring opening catalyst, raise the temperature to 20-70 ℃, and then add epichlorohydrin dropwise, keeping the temperature constant after dropwise addition, to obtain the intermediate product chloropropylene glycol ether.
(2) Closed loop reaction: add 0.1-0.3wt% propylene glycol as Phase-transfer catalyst in the intermediate product synthesized in the previous step, raise the temperature to 65 ～ 85 ℃, then drop 1.05:1 ～ 1.2:1 liquid alkali and epichlorohydrin, after dropping, accelerate the stirring to keep the temperature unchanged, so that the semi-finished product of polypropylene glycol PPG can be obtained;
(3) Water washing and dehydration: Add the semi-finished product of polypropylene glycol PPG obtained in the second step to water for washing, and then obtain the initial product until the pH value of the aqueous phase reaches 7. Then, remove toluene and water through distillation technology to obtain the finished product.
Method 2: Polypropylene glycol PPG has two OH groups in the chemical formula, which can be generated by introducing epoxy groups and reacting with epoxy chloride under the action of alkali. The specific steps are as follows:
Add the weighed polyether, Phase-transfer catalyst, ECH and solvent into the reactor, start stirring to dissolve the catalyst and evenly mix the reactants. At a certain temperature, slowly add solid alkali (or liquid alkali), and then react for about 5 hours at a certain temperature. Then, use water to evaporate the solvent and return it to the water separator through condensation. At this time, the solvent will overflow and return to the reactor. Remove solvent, water and ECH from the solution by Vacuum distillation. The resulting product is polypropylene glycol PPG.