Vinylidene chloride copolymers have a number of superior properties, most notably, a high barrier to the transport of oxygen
and other small molecules. As a consequence, these materials have assumed a position of prominence in the packaging industry.
At processing temperatures these copolymers tend to undergo degradative dehydrochlorination. The dehydrochlorination reaction
is a typical chain process with distinct initiation, propagation, and termination phases. It has been demonstrated that initiation
of degradation is strongly facilitated by the presence of unsaturation along the backbone. Such unsaturation may be introduced
via interaction of the polymer with a variety of agents which might commonly be encountered during polymerization or processing.
The presence of an unsaturated unit within the polymer generates an allylic dichloromethylene which may function as a major
defect (labile) site for the initiation of degradation. The conversion of these dichloromethylene units into non-reactive
groups would interrupt propagation of the dehydrochlorination reaction and lead to the stabilization of the copolymer. Potential
stabilization in the presence of metal formates has been examined using a vinylidene chloride/methyl acrylate (five mole percent)
copolymer and thermogravimetric techniques. The effect of the metal formate on the stability of the polymer reflects the relative
halogenophilicity of the metal cation present. Metal formates (sodium, calcium, nickel(II) and to a lesser extent lead(II),
cadmium, manganese(II) and magnesium) may be expected to be ineffective as stabilizers for vinylidene chloride copolymers.
At the other extreme, metal formates which contain cations sufficiently acidic to actively strip chlorine from the polymer
backbone, e.g., zinc formate, will function to enhance the degradation process. An effective carboxylate stabilizer must contain
a metal cation sufficiently acidic to interact with allylic chlorine and to facilitate its displacement by the carboxylate
anion. Copper(II) formate may possess the balance of cation acidity and carboxylate activity to function as an effective stabilizer
for vinylidene chloride copolymers.