Functionalization of polyolefins in the melt

Polyolefins with a controlled amount of functional groups can be obtained either by catalytic copolymerization of suitable monomers or by chemical modification of the obtained macromolecules by a free radical reaction in bulk. This paper describes the main aspects of the latter method which is at present the one more extensively used. Thus examples are discussed showing that the modification can be modulated to a great extent depending on feed composition and macromolecular structure. For instance in case of linear polyethylene conditions can be found by which the sole grafting reaction takes place and can be predicted with a simple mathematical model based on a reaction with first order kinetic with respect to the grafting monomer. Under these optimal conditions mixtures of comonomers can be used to introduce in one step two different reactive groups. On the other side it is shown that degradation is favoured by the extensive branching while linearity and double bonds favour crosslinking. Proper coagents are indicated able to limit degradation thus allowing crosslinking and grafting of functional monomers even in case of polypropylene. On the other side the use of transfer agents can hinder crosslinking of highly unsaturated polymers. Selectivity is also observed with preferential conversion of vinyl versus internal double bonds and aliphatic blocks versus styrene blocks.

Key words: functionalization, polyolefins, functionalization kinectics, ethylenepolymers .propylene polymers, styrene polymers, maleic acid derivatives.