Mechanical cleaving of polymer chains

In both cases, the process gives rise to mixtures of block copolymer and homopolymer(s). 

WWWWWV MjM2 AAVWWW i vwvwwwv M jMj Wwvww, AWWWWV M7M2 WWVWW(i 

---

The recycling of PET is an important environmental topic as well as a commercial opportunity due to its widespread use, abundance and availability in bottles, packaging and fibres. While mechanical recycling of PET is now well established, newer chemical recycling techniques rely on depolymerization routes which cleave the polymer chains into new monomer building blocks (see Chapter 16). 

The fact that functionalization of polymers and small molecules is observed to occur predominately on terminal (methyl) carbon atoms does not imply that the oxyfluorination reaction is truly selective. Although the reaction mechanism has not been studied in detail, it is undoubtedly a free-radical process. Molecular oxygen reacts spontaneously with the fluorocarbon—hydrogen radicals generated by fluorine during the fluorination process. Acid fluorides are retained on terminal carbon atoms because they are stable in 1 atm of elemental fluorine. Hypofluorites, which may be short-lived intermediates of oxygen reactions with methylene radical sites along the carbon chain, are not observed in the functionalized polymers. It is probable that, if they are intermediates, they are cleaved and removed by the excess elemental fluorine. 

On the other hand, in arranged domains of macromolecules, polymer chains can be cleaved more easily than in amorphous regions. Sudi a conclusion ensues from the fact that after a disruption of a polymer chain, entropy of the system may rise more in an arran d macromolecular state than in random coils [57]. Since generation of radicals is more effective in an amorphous ase, the radiation transformation proceeding by a radical mechanism will occur there preferentially, and radiation destruction will be faster in orient (strained) macrcanolecules of an amorphous state. 

The polydispersity of sample A is rather high. This is due to a fimgal infection of the extracted polymer. It seems that the polymer chains did undergo some cleaving by extracellular depolymerases from the fungi, which led to increased PD and a rather low value of Mn. This is a mechanism also responsible for the biodegradation of these polymers in a natural envirorunent. 

The two radical fragments of the polymer cleaved by mechanical strain, Rp and R -, can now react with the rest of the polymer sample to produce higher molecular weight products of connected, polymer chains, as crudely illustrated in equation 10. The actual reactions leading to the formation of the crosslink may be multistep... 

---