Polymerizations of Lactams

Polymerizations of lactams produce important commercial polymers. The polymerization reactions, therefore, received considerable attention. Lactam molecules polymerize by three different mechanisms: cationic, anionic, and a hydrolytic one (by water or water releasing substances). The lactam ring is strongly resonance stabilized and the carbonyl activity is low. Nevertheless, the ring-opening polymerizations start with small amounts of initiators through trans-acylation reactions. Fairly high temperatures, however, are needed, often above 200C. In all such reactions, one molecule acts as the acylating agent or as an electrophile while the other one acts as a nucleophile and undergoes the acylation. Generally, the initiators activate the inactive amide groups causing them to react with other lactams through successive transamidations that result in formations of polyamides. Both acids and bases catalyze the transamidation reactions. The additions of electrophiles affect increases in the electrophilicity of the carbonyl carbon of the acylating lactam. The nucleophiles, on the other hand, increase the nucleophilic character of the lactam substrate (if they are bases).

All initiators can be divided into two groups. To the first one belong strong bases capable of forming lactam anions by removing the amide proton. This starts the anionic polymerization reaction. To the second one belong active hydrogen compounds capable of protonating the amide bond and thereby affecting cationic polymerization [114]. Side reactions are common in lactam polymerizations. Their nature and extent depends upon the concentration and character of the initiators, the temperatures of the reactions, and the structures of the lactams. When cationic polymerizations of lactams are initiated by strong acids, strongly basic amidine groups can be produced. These groups bind the strong acids, inactive the growth centers, and decrease the rate of polymerization. Use of strong bases to initiate polymerizations of lactams possessing at least one a-hydrogen also result in side reaction. Compounds form that decrease the basicity of lactams and polyamides and slow the polymerizations. Also, side reactions give rise to irregular structures, namely branching. The ring-opening polymerization reactions depend upon thermodynamic and kinetic factors, and on the total molecular strain energies of the particular ring structures. Six-membered d-Valero lactam is the most stable ring structure and most difficult to polymerize. Also, presence of substituents increases the stability of the rings and decreases the ability to polymerize.

اخر الاخبار

اخبار العتبة العباسية المقدسة

المجمع العلمي يقيم برنامجًا قرآنيًّا رمضانيًّا في جامعة الكوفة

الحلقة 21 من جائزة العميد القرآنية تشهد تأهل القارئ محمد حسن زاده من أفغانستان إلى المرحلة النهائية

موكب أهالي كربلاء يحيي ذكرى شهادة الإمام علي (عليه السلام) عند مرقده الطاهر

لليوم الثالث.. شعبة الخطابة تنظم مجالس العزاء لإحياء ذكرى شهادة الإمام علي (عليه السلام)

المزيد

الآخبار الصحية

تأثير اللياقة البدنية على الدماغ

تجربة سريرية تظهر فوائد اللوز للمصابين بالسمنة

اكتشاف طريقة غير متوقعة لتقليل خطر الإصابة بالسكري

خمسة مؤشرات صحية مهملة قد تنقذ حياتك

المزيد

الآخبار التكنلوجية

علماء الجيولوجيا يفكون لغز الصدع العملاق تحت الماء في المحيط الأطلسي

تحذير جديد: الاحترار العالمي يتسارع وقد نكسر حاجز 1.5 درجة قبل 2030

الصين تكشف عن ألياف كربون تفوق قوة الفولاذ بـ10 مرات

الجهاز المناعي يظهر دورا غير متوقع في صحة العظام

المزيد

مواضيع ذات صلة

Spontaneous Alternating Zwitterion Copolymerizations

Copolymerization of Cyclic Monomers

Ring-Opening Polymerizations of Cyclic Sulfides

Cationic Polymerization of Lactams

Special Catalysts for Polymerizations of Lactones

Special Catalysts for Polymerizations of Lactones

Polymerization of Lactones by Coordination Mechanism

Polymer-Based Solar Cells

Photo-Conducting Polymers That Are Not Based on Carbazole

Photoconductive Polymers Based on Carbazole

Photo-Conducting Polymers

Liquid Crystalline Alignment