Polyvinylpyridine and its copper chelate

A rapid initial drop in molecular weight followed by a slower decrease is observed when polyvinylpyridine is heated at 250°C [85]. This behaviour is qualitatively similar to that of polystyrene. Scission of weak links may be involved in the fast decay of molecular weight, but random scission may also explain the shape of the curve. As in the case of polystyrene, the mechanistic problem is very complex and many more experiments are needed to solve it. Chelation of 2- and 4-polyvinylpyridine makes those polymers less heat-resistant chain scissions already occur at 100°C while the uncomplexed polymer suffers no damage at this temperature. On heating, a change in the absorption spectrum of 2-polyvinylpyridine copper chelate dissolved in 1M HC1 is observed a new peak is formed at 

420 nm, the absorbance of which increases linearly with heating time. Most probably a redox reaction is responsible for the initiation of this degradation. Such a redox reaction has been identified in the polymerization of vinylpyridine in the presence of cupric acetate. A one-electron transfer from Cu2 + ion to vinylpyridine in a complex including two monomers per metal ion has been shown to initiate the polymerization [86]. 

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