Oxidation of Step-Growth Polymers

Oxidation of step-growth polymers follows the paths that are similar to oxidation reactions of organic molecules. Thus, oxidation of poly (ethylene terephthalate) was shown to proceed as follows [529]:

During thermal oxidation of polyamides, the N-vicinal methylene group is the preferred side of attack [531]. The reactivity depends, apparently, on the conformation of the amide group because an interaction takes place between the p-electronic system of the carbonamide group and its C–H bonds. In polycaprolactam, there exists a statistical distribution of both gauche and trans-conformations. The N-vicinal methylene groups in the trans-conformations to the amide groups are much more reactive than gauche [531]. When the oxidation of a polyamide occurs through an attack by NO₂ or ozone, then the amide groups themselves are subject to the attack [532]:

This appears to take place with hydrogen-bonded amide groups as well. The reaction, however, is inhibited by benzaldehyde or by benzoic acid. When the degradation does take place, it occurs at random [532]. Thermo-oxidative degradation of polyoxyglycols is reported to occur typically by a free-radical mechanism with the formation of hydroperoxides. The decomposition of the peroxides leads to formation of acids and carbonyl compounds [533]. A study of thermal oxidation of oligomers (molecular weight approximately 1,900) of polyoxypropylene glycols showed that at 70–120C the end hydroxyl groups are not responsible for degradation and that chain ruptures occur through decomposition of the hydroperoxides [534]: Two types of cleavage are possible. One can take place through the carbon-to-carbon single bonds as follows:

The other type of cleavage can occur through the oxygen–carbon bonds:

Both long and short molecular chains undergo degradation in an identical manner. The secondary radicals that form as a result of the decomposition of the alkoxy radical accelerate the oxidation process. It transforms into a chain process with an accompanying formation of various compounds. The products are alcohols, aldehydes, and ketones. The aldehydes are easily oxidized into peracids that degrade further into radicals. Thermal–oxidative degradation of polysulfones was studied at 280C [535]. The oxidation is a radical chain reaction with the initiation consisting of hydrogen abstraction from a methyl group:

The process then continues with formation of alkyl peroxide radicals, isomerization, breakdown, and formation of oxygen-containing compounds like aldehydes, and ketones. In the oxidative pyrolysis of poly-p-xylene, the oxygen attacks methylene groups first to form hydroperoxides [536]. This is followed by chain cleavage:

اخر الاخبار

اخبار العتبة العباسية المقدسة

العتبة العباسية المقدسة تعلن تأجيل مؤتمر معالم الحياة الطيبة عند أهل البيت (عليهم السلام) الدولي الثاني

قسم العلاقات العامة يقيم أمسية رمضانية ثقافية لطلبة الأقسام الداخلية في جامعة بابل

قسم الشؤون الفكرية ينظم ختمة قرآنية رمضانية في دولة تشاد بإفريقيا

ضمن مشروع بيوت النور.. المجمع العلمي ينظّم أمسية قرآنية رمضانية في كربلاء

المزيد

الآخبار الصحية

الماء المملح.. فائدة حقيقية أم "صيحة زائفة"؟

عادة بسيطة تدعم الصحة وتحافظ على الوزن المثالي

الغذاء النباتي يقلل مخاطر السرطان.. مع استثناء مهم

الحليب قليل أم كامل الدسم.. أيهما أفضل؟

المزيد

الآخبار التكنلوجية

أنثروبيك تتحدى البنتاغون.. وترامب يأمر بوقف التعامل معها

ميزة جديدة من "إنستغرام" لحماية المراهقين من الانتحار

الأولى من نوعها.. "تقنية مذهلة" في هاتف سامسونغ الجديد

لماذا تشعر المرأة بالألم أكثر من الرجل؟.. دراسة تجيب

المزيد

مواضيع ذات صلة

Photo-Oxidative Degradations of Polymers

Hydrolytic Degradation of Polymers at Elevated Temperatures

The Termination Reaction

صناعة حمض الكبريتيك

تركيب حامض الكبريتوز

كلوريد الثيونيل Thionyl Chloride

حامض الكبريتوز: Sulphureous Acid

مركبات الكبريت مع الأكسجين

مركبات الكبريت مع الهيدروجين

الكبريت الغروي

الحصول على الكبريت من المناجم Sulphur Mining

الأشكال التأصلية للكبريت