Degradation of polymer chain

A PP sample after ozonization in the presence of UV-irradiation becomes brittle after 8 hrs of exposure, whereas the same effect in ozone is noticeable after 50-60 hours.Degradation of polymer chain occurs as a result of decomposition of peroxy radicals. The oxidation rapidly reaches saturation, suggesting the surface nature of ozone and atomic oxygen against of PP as a consequence of limited diffusion of both oxygen species into the polymer. Ozone reacts with PP mainly on the surface since the reaction rate and the concentration of intermediate peroxy radicals are proportional to the surface area and not the weight of the polymer. It has been found that polyethylene is attacked only to a depth of 5-7 microns (45). 

Most properties of polypropylene are similar to polyethylene but polypropylene has higher softening point and at 140°C polypropylene still retains its shape. Polypropylene is more susceptible to oxidation by air at higher temperature. Cross-linking, chlorination and other reactions lead to degradation of Polymer chain and are not very useful commercially. 

The chemistry of the solid-state polycondensation process is the same as that of melt-phase poly condensation. Most important are the transesterification/glycolysis and esterification/hydrolysis reactions, particularly, if the polymer has a high water concentration. Due to the low content of hydroxyl end groups, only minor amounts of DEG are formed and the thermal degradation of polymer chains is insignificant at the low temperatures of the SSP process. 

Ultrasonic devulcanization, therefore, causes significant degradation of polymer chains. A simple model based on a purely topological consideration was proposed and simulation of the process was carried out. In the model they have assumed a breakup... 

The cryo-grinding process is the first preference [1], the low temperature preventing the chemical-related degradation of polymer chains. Moreover, the rubber powder should preferably be ultrafine [2]. 

Positive photoresists have been increasingly important because of their higher resolution capability and better thermal stability. They become more soluble in exposed areas by increasing their acidity or by undergoing bond scission and degradation of polymer chains. 

Prevailing shear rate in injection and flooding process (besides the usual shear thinning behaviour of polymer solutions, extreme shear conditions can result in mechanical degradation of polymer chains). 

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