Free Radical Reactivity and Compatibilization of Polyolefins

The foeus on free radical reactivity is particularly important for the polymer blends in which none of the polymer components contain functional groups for condensation reactions, for example the polyolefins. The purpose of using peroxide in a proeess of in situ compatibilization of polyolefin blends is to trigger the polymer modification, taking advantage of the high sensitivity (and reactivity) of polyolefins to free radicals. 

A common example for polyolefin blends are the blends of polyethylene/polypropy-lene (PE/PP). PE and PP are immiscible due to their difference in molecular structure. Although both have a high reactivity in free radical reaction, the compatibilization of a PE/ PP blend cannot generally be achieved through reactive blending of PE and PP melts by simply using a radical initiator (such as peroxide) [2-4]. This is due to the different side reactions of PE and PP when their molecular chains are attacked by free radicals. Both PE and PP molecules can form a macromolecular free radical when a hydrogen molecule is abstraeted from them. Then the macro-radicals of PE tend to combine with each other. 

Theoretically, it is possible to have a reciprocal grafting reaction between the macroradicals of PE and PP, as shown below in the reaction Eq. (9.4). 

A logical deduction from the results mentioned above is that a key requirement for ftie in situ compatibilization process for PE/PP blends may be 

In the interest of this chapter s theme, the work of Scott et al. confirmed that, on the one hand, the process of free radical reaction in the polymer melt can be applied to the PS. On the other hand, the free radical reactivity of PS is so weak that a very long reaction time is needed when a peroxide alone is used in the melt blending process. The 

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