Scission and Acid End Groups

Irradiation of polytetrafluoroethylene produced acid end groups and the scission occurs in both the crystalline and amorphous regions. When a sample of polytetrafluoroethylene is used with a high initial crystallinity, irradiation decreases the crystallinity 23S). 

Effect of Fiber Degradation on the Corrosion Solution. Hydrolysis and oxidation of protein and cellulose have been described in the literature primarily with the focus on degradation in industrial processing conditions. In alkaline conditions, amino acids are released from silk in a chain unzipping mechanism in acidic conditions, the scissions are random (8,9). As the polymer deteriorates, free carboxyl and amine end groups are formed. Tyrosine oxidizes to a quinone this reaction gives aged silk its yellow coloration. Amorphous areas of the fiber are attacked first. 

Scheme 1.73. Acid hydrolysis of PET producing chain scission and generation of acid and alcohol end groups. The carboxylic acid catalyses further hydrolysis.

Scheme 1.74. The mechanism for acid hydrolysis of polyamide leading to chain scission and amine and carboxylic acid end groups. After Zaikov (1985).

The My, of unmodified PA-6 significantly increases after a residence time of 30 min in the melt from 23 to 64 kg mofi. Clearly, the post-condensation reaction which occurs between the amine and carboxylic acid end groups in the melt at 260 °C cannot be avoided. For PA-6 whose amine end groups have partially been blocked, a comparable treatment in the melt leaves the M nearly unaffected (a change from 20 to 21 kg mofi ). These results clearly point to an increased melt stability of the partially end-capped PA-6. The fact that the molecular weight of PA-6 slightly decreases upon the modification in the supercritical fluid indicates that more low-molecular-weight material is present as a result of some chain scission. 

Scission of some of the C—C bonds results in the formation of carbonyl end-groups. Aldehyde and acid ends are expected to form according to the reactions ... 

Under UV irradiation poly(dimethylacrylimide) (4.68) decomposes by elimination of isocyanic acid (HNCO), which results in main chain scission with the formation of olefin and ketene end-groups, as shown below [947] ... 

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