The effect of metal acetylacetonates on the thermal degradation of poly(methyl methacrylate): part II-Manganese (III) acetylacetonate

The effect of small amounts of manganese(III) acetylacetonate on the thermal stability and degradation mechanism of radically polymerised poly(methyl methacrylate) (PMMA) has been examined, using a similar approach to the previous study of the effect of the corresponding cobalt(III) chelate. Like Co(acac)₃, the manganese salt initially breaks down to the bis-chelate with loss of an acac radical, which can induce monomer production in the polymer at quite low temperatures. Unlike Co(acac)₃, however, Mn(acac)₃ can complex with the ester side groups of PMMA. In practice, this difference is not reflected in the degradation behaviour and it is concluded that decomposition of the bis-chelate and the effects of its ability to complex with ester side groups are more important. Although there is some destabilisation of the polymer at low temperatures, the main effects are of stabilisation at the main decomposition stage, due to the formation of some modified structures in the polymer backbone which act as blocking groups for the monomer-producing depropagation and consequently greatly reduce the zip length for this process. Small amounts of other products, including some chain fragments, are formed in addition to monomer, which is the sole degradation product from the pure polymer.