Chapter 77: Purchase of raw materials

After the 　　 group meeting, Chen Wanqing said happily:
　　 "With a budget of 15,000, I can buy a lot of monomers and raw materials."
　　 "Where do we usually buy medicines?" Xu Qiu said.
　　 "You can check the commonly used reagents from the major reagent suppliers, such as Bailingwei, Anaiji, Alatin, Sinopharm, etc." Chen Wanqing said:
　　" After confirming, you can place an order on the school’s drug warehouse website and entrust them to purchase on your behalf.
　　When choosing reagents, the first thing to look at is the purity. The higher the purity, the better. For synthesis, chemical purity is generally sufficient. For devices, analytical purity or higher is usually used.
　　 Then look at the packaging. If it is a liquid solvent, choose a package of 100 ml, 500 ml, 1 liter, etc. according to your needs.
　　 Next, see if there are other special requirements, such as whether it is equipped with molecular sieves, which are mainly used for drying and removing water.
　　 Like if we use it in a glove box, molecular sieves are not needed, because the water content in the environment is very low, and the addition of molecular sieves will bring impurities instead.
　　 But if it is used outside and the water content of the reagent is required, it is best to choose a molecular sieve.
　　 Finally, look at the price. Generally, you can buy directly below 1,000 yuan. If it exceeds 1,000..."
　　 "Just lower the requirements and find a more cost-effective one?" Xu Qiu asked.
　　 "Almost, if you really need it and there is no cheap alternative, you can also ask Teacher Wei for instructions and buy." Chen Wanqing said:
　　" In addition, it should be noted that some medicines are futures instead of spot products, and they may not arrive until one or two months after they are sold. Such drugs generally need to be shipped from abroad.
　　 But it’s not troublesome, because we bought them directly from their domestic branch, so we don’t need to report to customs ourselves.
　　 If you are looking for a foreign company to buy medicines, such as PCBM materials we buy, you must declare in the name of carbon when you pass the customs. "
　　 "Then are our monomer materials also bought from these reagent vendors? I always feel that these materials are a bit niche." Xu Qiu said.
　　 "General solvents will be bought from reagent vendors," Chen Wanqing said:
　　"For example, most organic photovoltaic monomer materials are not available from reagent vendors, and you need to find a company that specializes in photovoltaic materials.
　　 For example, the P3HT and PTB7-TH polymers we bought were purchased from a photoelectric material company in Beijing. If we buy monomers, we usually go to another company in Shenzhen.
　　 usually use QQ to contact, they will send me a quotation from time to time, introducing their latest products and quotations.
　　 I feel that the only use of QQ now is to contact them. "
　　 After finishing talking, she took Xu Qiu to sit down, opened the PDF of Shenzhen Optoelectronics' quotation with her computer, and said:
　　" The previous monomers were bought from them. The monomers from his house are not only high in purity, but also relatively cheap, but there are a few types.
　　 However, I have seen it, this time we have all the monomers involved in the synthesis scheme, so don't worry about being out of stock.
　　 Let's first determine which ones to buy, and then send them the demand, then we should be able to bargain. "
　　 "Okay." Xu Qiu nodded and began to study the quotation.
　　 In the previous literature reading, he learned that he wanted to connect the D unit and the A unit to synthesize the D-A copolymer by using condensation polymerization.
　　Condensation reaction simply means that the two hands of the D unit hold a key each, and the two hands of the A unit hold a lock. There is no difference between the keys and the locks.
　　Mix a large amount of unit D with two keys and unit A with two locks in an equimolar ratio of 1:1.
　　Under proper reaction conditions, the key can be inserted into the keyhole to open the lock, and then the key will fall off together with the lock. Unit D and Unit A form a hand-in-hand state.
　　 corresponds to the synthesis reaction:
　　Key-D-key+lock-A-lock→key-D-A-lock.
　　The key and lock at the end can also be combined with other locks and keys, making the D-A chain longer and longer.
　　Finally, the structure of the polymer obtained is:
　　Key-D-A-D-......-A-D-A-lock.
　　At the beginning of the reaction, there are many D units with keys and A units with locks, which can easily form a hand-in-hand state.
　　 But in the later stage, the consumption of the key and the lock is almost the same. After the D unit and the A unit also form a long chain, the key and the lock are difficult to touch, and the reaction almost stops.
　　 This kind of condensation reaction has very strict requirements on the ratio of the two monomer materials. If the ratio is not 1:1, even if it is 1:0.9, the final molecular weight will be greatly reduced.
　　Because the number of keys is more than that of locks, a lot of similar to:
　　 Key-D-A-D-key, key-D-A-D-A-D-key, ... such a structure causes the reaction to stop.
　　 As for the specific synthesis method, there are two kinds.
"One is the Suzuki coupling reaction, and the other is the Stille coupling reaction.
　　 The key and lock of the former are borate/boronic acid groups and bromine groups, respectively.
"The latter are trimethyltin/tributyltin and bromine groups, respectively.
　　……
　　 "Senior sister, which type of condensation do we generally use, Suzuki or Stille?" Xu Qiu asked.
　　 "Relatively speaking, the Stille coupling reaction is better, and the monomers are also relatively complete," Chen Wanqing said after turning the conversation:
"However, there is a problem, that is, the monomer unit with trimethyltin/tributyltin is highly toxic. After being absorbed by the human body, it will cause heavy metal poisoning, and if it is serious, it will cause a lot of hair loss. "
　　 "Then we..." Xu Qiu tentatively said.
　　 "Let’s use Stille reaction. The dose we make is small. As long as protective measures are taken, it is not dangerous if it is swallowed, inhaled or directly contacted with the skin." Chen Wanqing said:
　　"Actually, I am not willing to do chemical synthesis. Not only tin reagents, but other solvents such as chloroform, dichloromethane, chlorobenzene, etc. are toxic, and they also have potential carcinogenic risks.
　　 However, it’s okay that we mainly do materials, but chemistry is miserable. Basically we deal with various toxic reagents every day. "
　　 "I heard that it has been circulating in the circle that men don't need furan and women don't need pyridine?" Xu Qiu said.
　　 "Yes, these two solvents are common reproductive toxicity, and they are aimed at men and women," Chen Wanqing said:
　　 "There was a postdoctoral fellow in my original group. At that time, he took a one-year leave of absence before having a child, fearing that it would affect future generations."
　　……
　　 Although the synthesis is dangerous, the experiment will continue.
　　 "Senior sister, I have already decided which monomers to buy," Xu Qiu said:
　　 "It's just that many of them start at 500 mg or 1 gram. Can I discuss with them and sell at 200 mg?"
　　 "200 mg, isn't it gone after one reaction?" Chen Wanqing saw Xu Qiu's serious expression and said:
　　 "Okay, let me try it for you. Which monomer do you want?"
　　 "This, this, and this." Xu Qiu said, pointing to the quotation.
　　 "Are these two?"
　　 "No, buy 1 gram for each of these two, 200 mg for all other monomers on this page."