Chloroprene Rubber, Poly(2-chloro-1,3-butadiene)

2-Chloro-1,3-butadiene (chloroprene) was originally synthesized in 1930. The material can polymerize spontaneously to an elastomer that has good resistance to oil and weathering. Commercial production of chloroprene rubber started in 1932. Since then, many types of polymers and copolymers were developed with the trivial generic name of neoprene. The monomer can be prepared from acetylene:

It can also be formed from butadiene.

Chloroprene is polymerized commercially by free-radical emulsion polymerization. The reaction is carried out at 40C to a 90% conversion. A typical recipe for such an emulsion polymerization is as follows [127]:

When the polymerization reaches 90% conversion, the reaction mixture is cooled to 20C and tetraethyl thiuram disulfide is added. This is done to prevent the pendant unsaturation in the polychloroprene backbones from cross-linking or forming branches. An unmodified polymer is difficult to process even at a 70% conversion. To overcome this, a sulfur–tetraethyl thiuram modification is carried out. When the product is treated with the thiuram, an exchange reaction takes place to yield a stable, thiuram-modified polymer of reduced molecular weight. It is believed that the reaction takes place through cleavage of the sulfur links, formed during polymerization in the presence of sulfur, and formation of free radicals [128]

After the reaction with tetraethyl thiuram disulfide is completed, the latex is acidified with acetic acid, short of coagulation. The rubber is then recovered at a low temperature (about 15C) in the form of sheets by deposition of the latex on cooled rotating drums [127, 128]. The polymer, formed by this technique, consists of about 85% of trans-1,4 units, 10% of cis-1,4 units, 1.5% of 1,2 units, and 1.0% of 3,4 units. The polymer is essentially linear with a molecular weight equal to approximately 100,000. The sulfur-modified polychloroprenes are sold under a trade name of Neoprene-G. An unmodified version prepared with mercaptan chain transferring agents (Neoprene W) is a polymer with a molecular weight of about 200,000 [128, 130]. Table 6.9 lists the structures of polychloroprenes that form by free-radical polymerization at different temperatures. Chloroprene polymerizes by cationic polymerization with the aid of Lewis acids in chlorinated solvents. When aluminum chloride is used in a mixture of ethyl chloride–methylene chloride solvent mixture at 80C, the polymer has 50% 1,4 units [131, 132]. If it is polymerized with boron trifluoride, the product consists of a 50–70% 1,4-adducts. A very high trans-1,4 poly (2 chloro-1,3-butadiene) forms by X-ray radiation polymerization of large crystals of chloroprene at 130 to 180C.Itis 97.8% trans-1,4 [130]. Presumably the mechanism of polymerization is free radical.

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اخبار العتبة العباسية المقدسة

العتبة العباسية المقدسة: نهج البلاغة مصدر صافٍ للفكر والمعرفة ومحصِّنٌ من الشبهات

العتبة العباسية المقدسة تطلق محاضرات محفل نهج البلاغة الأسبوعي في ذي قار

العتبتان المقدستان الحسينية والعباسية تدعوان للمشاركة في مهرجان الشموع بنسخته السادسة والعشرين

بالتعاون مع مستشفى الكفيل.. قسم الشؤون الطبّية يواصل إقامة البرنامج التدريبي لملاكاته النسوية

المزيد

الآخبار الصحية

الصحة العالمية تكشف حقيقة انتشار فيروس نيباه خارج الهند

متى يصبح محيط الخصر "مؤشر خطر"؟

دراسة تكشف دور "العوامل الوراثية" في تحديد عمر الإنسان

رائحة كريهة في الجسم.. "علامة خفية" أخطر مما تتصور

المزيد

الآخبار التكنلوجية

مايكروسوفت تكشف عن الجيل الثاني من شرائحها للذكاء الاصطناعي

خرافة "ثمانية أكواب يوميا".. كم من الماء يحتاج جسمك فعليا؟

هل توجد حياة خارج كوكبنا؟.. اكتشاف جديد يثير اهتمام العلماء

اكتشاف الخلايا المسؤولة عن فقدان ذاكرة الطفولة

المزيد

مواضيع ذات صلة

Polystyrene Prepared by Ionic Chain-Growth Polymerization

Preparation of Polystyrene by Free-Radical Mechanism

GR-N Rubber

GR-S Rubber

Cyclopolymerization of Conjugated Dienes

Special Polymers from Dienes

Synthetic Polyisoprenes

High Molecular Weight Polybutadiene

Liquid Polybutadiene

Polybutadiene

Ionomers

Copolymers of Ethylene with a-Olefins and Ethylene with Carbon Monoxide