Chapter 87: Post-reaction processing

　　 Chen Wanqing added about 10 milliliters of toluene to her reaction flask, reheated it to 70 degrees Celsius and started stirring.
　　 "Senior sister, how many times have you done polymerization before?" Xu Qiu asked curiously.
　　 "About four or five times, I studied with Teacher Wei for a month before, and at that time I still borrowed other people's labs to do experiments." Chen Wanqing said.
　　 "Have you successfully synthesized a polymer?" Xu Qiu asked.
　　 "Of course I did, it succeeded... this time," Chen Wanqing said:
　　 "Don't talk about this, my product has dissolved and can be post-processed."
　　 When talking about the number of successes, her voice was extremely small, and Xu Qiu didn't hear it clearly.
　　 Estimated to be zero times? once?
　　 Xu Qiu shook his head, did not continue this topic, and said:
　　 "I remember that after the reaction is over, the capping reaction will be carried out."
　　 "Right," Chen Wanqing said:
"The end-capping reaction" means that thiophene with trimethyltin on one side and thiophene with bromine group on one side are reacted with the polymer.
"This can remove the useless groups at the end of the polymer and reduce the defects of the polymer material in the film state.
　　 But my reaction is so bad this time, there is no need to block it. "
　　 Xu Qiu thought for a moment, and decided not to make a capping reaction.
　　 On the one hand, there is a class meeting at 7 o'clock in the evening, and the time will be tight;
　　 On the other hand, although his balloon was not completely deflated like Senpai, it was only as big as an incandescent lamp, and it should have leaked some air in.
　　Moreover, the amount of solvent used in this reaction is too much, and it is estimated that the molecular weight of the product obtained will not be very high.
　　 "Senior sister, I won't make a capping reaction anymore." Xu Qiu said.
　　 "Okay, let's do post-processing directly." Chen Wanqing said:
　　"The products we get include not only the high molecular polymers we need, but also some oligomers and small molecules.
　　 oligomers are polymers that have undergone polymerization, but their molecular weight is not high, and their photoelectric properties are usually poor.
"Small molecules" include trimethylstannide bromine, catalyst, and even unreacted monomer raw materials remaining in the solution.
　　 For these substances, we have to remove them from the product to obtain a clean polymer material.
　　In the first step, we will slowly drop the polymer solution into methanol.
　　 Because methanol is a polar solvent, it is also a poor solvent for polymers.
　　 So in this step, the polymer will be precipitated, and some small molecules and oligomers will be dissolved in the mixed solvent of toluene and methanol.
　　After filtering the solution, the solid material obtained is collected, and this is the crude product.
　　 Put the crude product in a Soxhlet extractor for further purification.
　　 Finally, dry high molecular polymer materials can be obtained by drying in a vacuum oven. "
　　 Xu Qiu nodded, this part of the inner school sister demonstrated and directly started the experiment.
　　 He took two disposable PE cups, added about 250 ml of methanol solvent, and then covered them with a piece of filter paper to prevent dust from falling in.
　　 Then, he touched the wall of the two-necked flask and judged that the temperature had dropped to about 50 degrees Celsius.
　　 After he shut down the reaction before, he removed all the other devices, leaving only a two-necked flask above the oil bath.
　　 In addition to allowing it to quickly cool to room temperature, it can also return the simethicone on the bottle wall to the oil bath.
　　 The viscosity of simethicone is very high. If you take out the bottle directly, you will get oil everywhere, and you need a lot of toilet paper to clean it up.
　　 Therefore, this oil control operation must be done.
After confirming the temperature of the polymer solution, Xu Qiu sucked the solution in the two-necked flask with a disposable dropper and slowly dropped it into the methanol solution.
　　 When the polymer solution was in contact with methanol, a blue flocculent precipitate was produced.
　　 After continuous dripping, the methanol solution also changed from colorless and transparent to blue, indicating that a lot of products were dissolved in methanol.
　　Because the molecular weight of the polymer is roughly in a normal distribution, there are many small molecules and oligomers, so the molecular weight of the remaining high-molecular polymers will naturally not be high.
　　 As expected, the reaction this time was not good.
　　 Xu Qiu was not too surprised, he changed another cup with methanol, and continued to drip the polymer solution.
　　 More than ten milliliters of the solution, it took five times to add all the drops, and two cups of turbid liquid with blue sediment floating.
　　He took two pieces of filter paper, folded them into a funnel, and filtered two cups of the solution.
　　 When the filtration started, the dripping speed of the solution was very fast, and then it became slower.
　　 After pouring all the solutions, Xu Qiu put a piece of filter paper on the filter device and put the device in a fume hood.
　　It is estimated that it will take several minutes to ten minutes to complete the filtration.
　　 So, Xu Qiu went to the fume hood next to him to check the progress of the senior sister.
　　 She is dropping the toluene solution of the product into methanol, and the addition is almost complete.
　　 Xu Qiu saw that the color of her methanol solution was darker than his.
　　 Chen Wanqing heard the movement and asked:
　　 "School brother, how are you? How does your product feel?"
　　 "Similar to yours," Xu Qiu said.
　　 "Hey," Chen Wanqing sighed:
　　 "This time we will both be expected to be cool, but let's take a look at the product Soxhlet, and then add another reaction today."
　　 "Okay, then I'm going to do the preparatory work." Xu Qiu said.
　　 Yesterday’s toluene can still be re-steamed. Just set up the device in order.
　　 There are only four oil baths, and the next Soxhlet extraction will take two more. If the toluene is not re-steamed in advance, the oil bath will not be enough.
　　 Thinking of this, Xu Qiu copied the four oil baths in the simulation laboratory again, and then said to Chen Wanqing:
　　 "Senior sister, can I apply for a few more oil bath pans with Teacher Wei? I feel that the four are not enough now."
　　 "Okay, there are indeed some shortages. I'll call him later and ask." Chen Wanqing said.
　　 After starting the toluene re-steaming device, Xu Qiu cleaned the glassware that was newly used today with ethanol solvent and put it in the oven.
　　……
After the product is separated out in methanol and filtered, it must be further purified by Soxhlet extraction.
　　 Chen Wanqing picked up the extraction tube for Soxhlet extraction and introduced:
　　" The Soxhlet extractor was used in Soxhlet extraction, which was also called fat extractor at first.
　　 From bottom to top, this device consists of three parts: a conical flask, an extraction tube, and a spherical condenser. The extraction tube is a special glass instrument with a siphon tube and a connecting tube on both sides.
　　 First wrap the sample in filter paper and put it in the extraction tube, then add a mixed solvent of methanol, acetone, and n-hexane in the Erlenmeyer flask, and finally insert the spherical condenser and connect the condensed water.
　　 Heating the Erlenmeyer flask, the mixed solvent vaporizes, rises from the connecting tube into the condenser tube, condenses into liquid and drips into the extraction tube to extract small molecules in the sample.
　　 When the liquid level of the mixed solvent in the extraction tube reaches a certain height, the solvent flows into the extraction bottle through the siphon.
　　The mixed solvent flowing into the extraction bottle will continue to be heated to vaporize, rise, condense, and then drip into the extraction tube, and so on, until the extraction is complete.
　　 It is generally believed that the color of the solution in the extraction tube becomes colorless and transparent, which indicates that the small molecules are basically removed. "