Molecular weight reduction mechanisms

They may also act as reactive super plasticisers to increase rubber flow while increasing the mechanical properties of the rubber. Viscosity reduction or polymer solvation and higher filler loading can be accomplished with less plasticiser. Flow is achieved through molecular rearrangement and not average molecular weight reduction of the rubber. 

The reduction in molecular weight of various fractions of crude oil is an important operation in petroleum chemistry. The process is called cracking. Catalytic cracking is usually achieved by passing the hydrocarbons over a metallic or acidic catalyst, such as crystalline zeolites at about 400-600 °C. The molecular-weight reduction involves carbocationic intermediates and the mechanism is based on the )8-scission of carbenium ions (equation 28). 

The molecular weight reduction, which is a first consequence of the mechanochemical act, is macroscopically reflected in the change of some mechanical properties, among them being the tensile strength [701]. Accordingly, the variation of with the parameters of ultrasonic treatment, especially with the time, can constitute an estimation criterion for the intensity of the mechanochemical processes which develop in the mechanically stressed material. 

Cullis and Hirschler proposed a detailed study on the mechanism of the thermal degradation of polymers [2, 40], which consists of two distinct reactions occurring simultaneously in the reactor. One is a random scission of links, causing a molecular weight reduction of the raw polymer, and the other is a chain-end scission of C-C bonds, generating volatile products [40]. 

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