Poly mechanical degradation

If a mechanical degradation of a solution of two polymers is carried out by high speed stirring, the formation of a block copolymer is not probable as the scission of polymer molecules at low concentration is not caused mainly by intermolecular interaction, such as by collision of molecules and through entanglements, but by displacements due to hydrodynamic forces in velocity gradients. Nakamo and Minoura (98) did obtain reaction by stirring a benzene solution of polyethylene oxide and poly(methyl methacrylate). 

If mechanical degradation of a polymer solution by high speed stirring is carried out with a vinyl monomer in an inert atmosphere the monomer will be polymerized by the free macroradical. Goto and Fujiwara, for example, studied poly(vinyl acetate vinyl acetate) agitated in an Homomixer at 30000 rpm in a nitrogen atmosphere at 65° C (99). They found that the polymerization rate, Vp, is proportional to the square root of the initial concentration of poly(vinyl acetate) ... 

Structures of volatile degradation products show that all these molecules were detached from the cyclolinear polymer by the mechanism first suggested for poly(dimethylsiloxane) by Thomas [4], In this mechanism, degradation starts with formation of an intermediate fourcentered structure, and then two siloxane bonds involved are rearranged. 

HAB08] Hablot E., Bordes P., Pollet E., et al, Thermal and thermo-mechanical degradation of poly(3-hydroxybutyrate)-based multiphase systems . Polymer Degradation and Stability, vol. 93, no. 2, pp. 413 21,2008. 

X—NHCOCHj ) (X = poly caprolactam chain) Mechanical degradation of polycaprolactam/ Solid polymer EPR/ 77 2H(a) 1.9 67Zakl... 

Figure 1.6 Intramolecular ester interchange mechanism of poly(glycolide) degradation (the intramolecular arrow indicates the direction in which the ester interchange occurs).

Badia, J.D., Stromberg, E., Ribes-Greus, A., and Karlsson, S. (2011) A statistical design of experiments for optimizing the MALDI-TOF-MS sample preparation of polymers. An application in the assessment of the thermo-mechanical degradation mechanisms of poly (ethylene terephthalate). Anal. Chim. Acta, 692, 85-95. 

Viscometric data for dilute and semidilute poly(acrylamide) solutions can often be fit to a Carreau model (63,64). It is wise to remember the cautions that were cited previously about mechanical degradation of the high molecular weight components of a polyacrylamide sample when analyzing rheological data. 

Booth [25] found on mechanical degradation of a narrow MWD poly-isoprene that the MWD broadens after severe shearing. It should be emphasized that even if the degradation is selectively near the chain midpoint, a rich, broad-spectrum energy source might break the chain over a broad range of chain positions. This may especially be the case in sonic irradiation. 

Butyagin investigated the mechanical degradation of polymers with quaternary carbon atoms in the main chain. He distinguished different radical types [24]. An unpaired electron was found (1) at the chain end for poly(methyl methacrylate) and for polyisobutylene (2) in the methyl group of the main chain of poly(methyl methacrylate) and (3) in the benzene ring in poly(a-methylstyrene). 

Fig. 3.30 Mechanical degradation of various polymers in nitrogen (continuous curves) and in air (broken curves) (1) gelatin (2) PVC (3) poly(vinyl alcohol) [13].

From turbidimetric titration curves, it was deduced that mechanical degradation of polystyrene in the presence of acceptors results in linear chain degradation products, whereas poly(methyl methacrylate) gave branched and cross-linked fragments [45]. 

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