Free-Radical Grafting Reactions to Polymers with Double Bonds

Carbon to carbon double bonds, either in the backbone or in the pendant groups, are potential sites for free-radical attacks. In addition to the double bonds, the hydrogen atoms on the neighboring carbons are allylic and potential sites for chain transferring. Because rubbers, natural and synthetic, possess such unsaturations, they are used extensively as backbones for various grafting reactions. Whether the reactivity of the initiating radical is important in determining grafting efficiency is not completely established. Graft copolymers of poly (methyl methacrylate) on gutta-percha, however, form in good yields when the initiator is benzoyl peroxide. Yet, when azobisisobutyronitrile is used, only a mixture of homopolymers forms. Work with 14C-labeled initiators shows that the primary radicals react both by addition to the double bonds and by transfer to the methylene group.

Grafting reactions to polybutadiene, however, proceed via chain transferring from the growing chain radical to the backbone . Nevertheless, strong evidence also shows that the initiator radicals can interact directly with polymeric backbones . When graft copolymers of polystyrene to natural rubber form, the chain length of the attached branches equals to the chain lengths of the unattached polystyrene homopolymer that forms simultaneously . This led to the following conclusions :

1. As the concentration of rubber increases, the length of the grafted branches diminishes, while their number remains the same.

2. When the concentration of the initiator increases, the length of the branches diminishes, but the number of branches increases.

 3. When the concentration of monomers increases, the length of the branches also increases, but their number diminishes.

 4. When the polymerization time increases, the length of the branches remains the same, but their number increases.

اخر الاخبار

اخبار العتبة العباسية المقدسة

قسم الشؤون الخدمية يهيئ أماكن لاستراحة الزائرين في محيط العتبة العباسية المقدسة

جناح العتبة العباسية المقدسة في معرض طهران الدولي للقرآن الكريم يشهد إقبالًا واسعًا

ضمن خطته الخاصة بشهر رمضان المبارك.. قسم المضيف يقدم 3500 وجبة إفطار يوميًّا للزائرين.

قسم الشؤون الفكرية يطلق مسابقة النور الزكي الرمضانية في ذي قار

المزيد

الآخبار الصحية

دراسة تحذر من الإفراط في ممارسة الرياضة.. كيف يضر دماءك؟

الطهي بزيت الزيتون.. مضر أم مفيد؟

دماغ الرضع في خطر.. دراسة تحذر من "العدو الخفي"

التمر بالحليب عند الإفطار.. "كنز صحي" في رمضان

المزيد

الآخبار التكنلوجية

أثر نفسي غير متوقع للرياضة.. مرتبط بالغضب

القمر يواصل الانكماش.. رصد تشققات حديثة على سطحه

إطلاق أول تطبيق مراسلة "مشفّر".. ثورة في عالم الدردشة

خلل تقني يؤجّل أول رحلة مأهولة إلى القمر منذ عقود

المزيد

مواضيع ذات صلة

Block Copolyesters

Block Copolymers

Miscellaneous Graft Copolymerizations

Preparation of Graft Copolymers with Ionic Chain-Growth and Step-Growth Polymerization Reactions

Graft Copolymer Formation with the Aid of High-Energy Radiation

Photochemical Syntheses of Graft Copolymers

Initiations of Polymerizations from the Backbone of Polymers

Preparation of Graft Copolymers with the Aid of Macromonomers

Free-Radical Grafting by Chain-Transferring Process

Vulcanization of Elastomers

Miscellaneous Exchange Reactions

Substitution Reactions of Poly (vinyl alcohol)