Radical polymerisation polar monomers

Ziegler Natta catalysts are characterised by low activities in both olefin/ polar monomer copolymerisation and polar monomer homopolymerisation. Homopolymers of polar monomers appeared in most cases to exhibit properties that were very similar to those of homopolymers obtained by radically initiated polymerisations this testifies to the radical mechanism that operates in such polymerisations [28]. 

It is to be noted in this connection that alkyl radicals normally formed during reduction of the transition metal compound in Ziegler-Natta systems [scheme (7)] do not initiate the radical polymerisation of olefins, in contrast to that of polar monomers. Most of the modified Ziegler-Natta catalysts for polar monomer polymerisation are characterised by low activities and lack of stereospecificity, producing polymers with properties that are very similar to those of polymers obtained by more conventional procedures for radical polymerisation [28],... 

The mechanism of the initiation of the radical polymerisation of polar monomers in systems comprising organometallic compounds Homogeneous anionic polymerisation of unsaturated monomers Metallopolymers... 

The fact that replacement of one methyl group by carboxyl or carboxylate changes the situation drastically, in that methacrylic acid and its esters are readily polymerised by radicals, may be due to the introduction of a high degree of polarity, which reduces the activation energy for the reaction of a radical with the monomer. 

Bailey [172] has combined the results obtained for the oxidation of chloroprene in the presence of azobisisobutyronitrile with those in the absence of initiator, to show that fej varies between 1 X 10-7 s 1 at 0°C and 1.65 X 10 6 s-1 at 35° C, the corresponding chain lengths being 90 and 170. Comparison of the reactivity of several monomers shows that chloroprene is oxidised faster even than styrene and Bailey has shown that the results agree well with predictions based on the reactivity of the double bond and the polarity of monomers involved ih co-polymerisation [173]. The system adopted describes the reactivity of monomers in co-polymerisation in terms of the rate coefficient for the addition of monomer 2 (polarity e2) to the radical of monomer 1... 

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