The action of ozone on polymers having unconjugated and cross- or linearly conjugated unsaturation: chemistry and technological aspects

We review the most recent work on the reaction of unsaturated polymers with ozone. Initially a series of diene polymers with unconjugated double bonds is considered and it is shown that the reaction rate with ozone (in solution) correlates with the free energy of reaction of each molozonide calculated according to MM+ and AM1 methods. The lower the free energy of reaction, the higher the reaction rate with ozone. Additionally, the reactivity of cured diene rubber with ozone in the solid state, in dry and moist ozone is discussed. A discussion is also presented about the crack growth of cured samples in the light of fracture mechanics. The reactivity and the peculiar mechanism of reaction with ozone of polymers having a long series of linearly conjugated double bonds is presented and discussed in comparison to an oligomeric model polyene compound: beta -carotene. A new mechanism is proposed to explain both the cis-trans isomerization (and vice-versa) and the experimental detection of radical cation species during the ozone treatment of polyenes. The final topic covers the reactivity with ozone of a unique polymer having a three-dimensional structure and 30 cross-conjugated double bonds: C-60 fullerene. The structure of the C-60 molozonide is reported together with calculations according to MM+ and AM1 which suggest the possible derivatives formed from the molozonide. Among the possible derivatives considered, the epoxide, experimentally observed, is among the most favoured. (C) 2001 Elsevier Science Ltd. All rights reserved.