Graft Copolymer Formation with the Aid of High-Energy Radiation

High-energy radiation sources include gamma rays from radioactive elements, electron beams from accelerators, and gamma rays from nuclear reactors. The energy radiated by these sources is sufficiently high to rupturing covalent bonds. This results in formations of free radicals. Several different methods are used to form graft copolymers. One of them is irradiation in open air. The free radicals that form scavenge oxygen and form peroxides and hydroperoxides on the polymeric chains. These are subsequently decomposed in the presence of monomers to form graft copolymers. When they are decomposed thermally [361], the hydroperoxides yield much greater quantities of homopolymers then do the peroxides. When, however, the decompositions are done at room temperature by redox mechanisms, formations of homopolymers are reduced [361, 362]. Another method is irradiation in vacuu. This results in formations of trapped radicals on the polymer back bones. After irradiation, the polymers are heated in the absence of oxygen and in the presence of vinyl monomers. The best results are obtained when irradiations are done at low temperatures, below Tg of the polymers. High degree of crystallinity is also beneficial, because mobility of the chains results in loss of trapped radicals. When the monomers are added, however, heat must be applied, but this can result in loss of some of the radicals. The third method is mutual irradiation in an inert atmosphere of polymers and monomers together. The polymers are either swelled or dissolved by the monomers. The relative sensitivities of the two species, the monomer and the polymer to radiation, can be important factors in this third procedure. Efficiency of grafting depends upon formations of free radicals on the polymer backbones. If only a small number of free radicals form, the irradiations produce mainly homopolymers. Also, if the polymers tend to degrade from the irradiation, block copolymers form instead. Presence of solvents and chain-transferring agents tends to lower the amount of the grafting [363]. It was also shown [409] that energetic heavy ions can also produce graft copolymers. The results appear similar to those obtained by electron beams. Also, many papers reported use of plasma for surface modification of films. The process can result in formation of graft copolymers when it is accompanied by an introduction of a monomer or monomers. One such example is a use of argon plasma to graft polyacrylamide to polyaniline films [410]. The near ultraviolet light plasma induces the reaction. Other monomers that can be grafted by this reaction are 4-styrenesulfonic acid and acrylic acid [410].

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

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 Reactions to Polymers with Double Bonds

Free-Radical Grafting by Chain-Transferring Process

Vulcanization of Elastomers

Miscellaneous Exchange Reactions

Substitution Reactions of Poly (vinyl alcohol)