Fullerene C60 as stabiliser for acrylic polymers

The influence of fullerene C-60 additives on thermal behaviour and thermodegradation of poly-n-alkyl acrylates, from butyl to heptyl, and of corresponding polymethacrylates was investigated by thermogravimetry in dynamical conditions and pyrolysis/gas chromatography in isothermal conditions at 400-650 degrees C. The fullerene is a well-known efficient acceptor of radicals and its presence influences the thermal degradation of acrylic polymers, shifting the decomposition process from a radical pathway to a non-radical mechanism. For poly-n-alkyl acrylates the addition of fullerene leads to increase in the yields of olefin and alcohol, degradation products coming from non-radical pathways. On the other hand, the yields of the pyrolysis products deriving from the random main-chain scission, i.e. monomer, dimer, saturated diester, trimer, corresponding acetate and methacrylate, decrease. The recorded temperatures of maximum weight loss (obtained by thermogravimetric experiments) are slightly increased by the presence of fullerene. The effect of fullerene is more noticeable in the thermal behaviour of poly-n-alkyl methacrylates, in fact the enhancements of the temperature of maximum weight loss are 19-25 degrees C. The mixtures containing fullerene give rise to a marked decrease of the monomer yield and, at the same time, an increase of olefin and methacrylic acid amounts. The fullerene acts as radical acceptor suppressing the unzipping process and favouring the non-radical side-chain reactions. (c) 2005 Elsevier Ltd. All rights reserved.