I Have a Research Support System

Chen Wanqing added about 10 milliliters of toluene to her reaction flask, reheated to 70 degrees Celsius and started stirring.

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 borrowed someone else's laboratory to do the experiment. Chen Wanqing said.

Have you successfully synthesized the polymer? Xu Qiu asked.

Of course I did, it succeeded... this time, Chen Wanqing said:

Let's not talk about this, my product has dissolved and can be post-processed.

When talking about the number of successes, her voice was so low that Xu Qiu couldn't hear clearly at all.

Estimated to be zero? once?

Xu Qiu shook his head, did not continue this topic, and said:

I remember that after the reaction is over, the capping reaction must be carried out.

That's right, Chen Wanqing said:

The end-capping reaction, that is, the reaction of thiophene with trimethyltin on one side and thiophene with bromine group on one side with the polymer.

In this way, the useless groups at the end of the polymer can be removed, and the defects of the polymer material in the film state can be reduced.

But I did such a bad reaction this time, so there is no need to block it.

Xu Qiu thought for a moment, and decided not to respond to blocking.

On the one hand, there is a class meeting at 7:00 pm, so the time will be tight;

On the other hand, although his balloon was not completely deflated like senior sister's, it was only as big as an incandescent light bulb, and some air should have leaked 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 do the blocking reaction anymore. Xu Qiu said.

Okay, then let's go straight to the post-processing. Chen Wanqing said:

The products we obtained include not only the high molecular polymers we need, but also some oligomers and small molecules.

Oligomers are polymers that have been polymerized, but the molecular weight is not high, and their photoelectric properties are usually poor.

Small molecules include trimethyltin bromide remaining in solution, catalysts, and even unreacted monomer raw materials.

For these substances, we need to remove them from the product to obtain a clean high molecular 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 blend solvent of toluene and methanol.

After filtering the solution, the resulting solid matter was collected and this was the crude product.

The crude product was further purified in a Soxhlet extractor.

Finally, the dry polymer material can be obtained by drying in a vacuum oven.

Xu Qiu nodded, and the senior sisters demonstrated in this part, and then started the experiment directly.

He took two disposable PE cups, added about 250 ml of methanol solvent, and then covered a piece of filter paper on top to prevent dust from falling.

Then, he touched the walls of the two flasks and judged that the temperature had dropped to about 50 degrees Celsius.

After he shut down the reaction before, he removed all other devices, leaving only a two-necked flask above the oil bath.

In addition to allowing it to cool down to room temperature quickly, it can also allow the simethicone oil on the bottle wall to return to the oil bath.

The viscosity of simethicone is very high. If you take out the bottle directly, the oil will be sprayed everywhere, and you need to use a lot of toilet paper to clean it.

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 dropwise addition, the methanol solution also changed from colorless and transparent to blue, which indicated that many products were dissolved in methanol.

Because the molecular weight of the polymer roughly presents a normal distribution, and now there are many small molecules and oligomers, the molecular weight of the remaining high molecular weight polymers will naturally not be high.

Sure enough, the reaction this time was not very good.

Xu Qiu was not too surprised. He changed to another cup filled with methanol and continued to add the polymer solution drop by drop.

It took five times to add more than ten milliliters of the solution, and two cups of cloudy liquid with blue precipitates were obtained.

He took two pieces of filter paper, folded them into a funnel shape, and filtered two cups of solution separately.

At the beginning of the filtration, the solution dripped quickly, and then it became slower.

After pouring out all the solutions, Xu Qiu covered the filter with a piece of filter paper and put the device in a fume hood.

It is estimated that it will take a few minutes to ten minutes for the filtration to complete.

So, Xu Qiu went to the nearby fume hood to check on the progress of the senior.

She is adding the toluene solution of the product dropwise to 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:

Student, how are you? How does your product feel?

It's about the same as yours. Xu Qiu said.

Hey, Chen Wanqing said with a sigh:

We're both going to be cool this time, but let's take a look at the Soxhlet extraction product, and then post another reaction today.

Okay, then I'll go do the preparations. Xu Qiu said.

Yesterday’s toluene can still be used for re-steaming, as long as the devices are set up in order.

There are only four oil baths, and the subsequent Soxhlet extraction will take up two more. If the toluene is not re-distilled in advance, the oil bath will not be enough for the reaction.

Thinking of this, Xu Qiu copied the four oil baths in the simulation laboratory again, and then said to Chen Wanqing:

Senior sister, can you apply to Teacher Wei to buy more oil baths? I feel that four are not enough now.

Okay, it's indeed a little short, I'll call him and ask about it later. Chen Wanqing said.

After starting the toluene redestillation device, Xu Qiu cleaned the newly used glass instruments with ethanol solvent and put them in the oven.

...

After the product is precipitated in methanol and filtered, it is further purified by Soxhlet extraction.

Chen Wanqing picked up the extraction tube used for Soxhlet extraction, and introduced:

The Soxhlet extraction uses a Soxhlet extractor, which was also called a fat extractor at first.

This device consists of three parts from bottom to top: Erlenmeyer flask, extraction tube, and spherical condenser. The extraction tube is a special glass instrument with siphon tubes and connecting tubes on both sides.

First, wrap the sample in filter paper and put it into the extraction tube, then add a mixed solvent of methanol, acetone, and n-hexane into the Erlenmeyer flask, and finally insert a spherical condenser tube to connect the condensed water.

Heating the Erlenmeyer flask, the mixed solvent vaporizes, rises from the connecting pipe into the condenser pipe, condenses into a liquid and then drops into the extraction pipe to extract the small molecular substances 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 continues to be heated, vaporized, rises, condenses, and drops 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, indicating that the small molecular substances are basically removed.

Thanks to _xszx, Ojisang who loves to read books, and brother Wuming Yi 1 for their 100-point rewards.