Degradation and stabilization of polycyanoacrylates

Polycyanoacrylates were found to be inherently unstable. Even in the absenc e of a deliberately added strong base, their molecular weights decreased dr astically on standing in solution in accord with observations by Ryan and M cCann (Makromol Chem Rapid Commun 1996, 17, 217). The initial high molecula r weight polymer disappeared over the course of a few hours in solution and was replaced by a much lower molecular weight material. For polymers made by anionic polymerization, the entire sample degraded, but for polymers mad e by free-radical polymerization, only a portion of the sample was affected . This behavior was consistent with the mechanism proposed by Ryan and McCa nn, in which the polymer chains are in dynamic equilibrium with their monom ers and the polymer degrades from its chain terminus. Surprisingly, the deg radation in molecular weight even occurred slowly in the solid state. The d egradation was inhibited by acids and could be prevented by free-radical co polymerization with small amounts of more stable monomers. (C) 1999 John Wi ley & Sons, Inc.