Comparative evaluation of polycyanoacrylates.

Cyanoacrylate esters (CA) and their corresponding polymers (PolyCA) are used as general and medical adhesives, biodegradable carriers for controlled drug delivery, and as agents for fingerprint development in forensic science. Most reports of cyanoacrylate are on ethyl or 2-octyl cyanoacrylate ester with little attention to other esters. It is the objective of this study to determine the differences amongst cyanoacrylate esters regarding their synthesis, chemical characterization, hydrolytic degradation, and thermal and mechanical properties. Cyanoacrylate polymers of short and long alkyls or oxy-alkyls, cyclic, and aromatic esters have been synthesized and evaluated. All monomers form polymers when exposed to triethylamine vapours possessing molecular weights in the range of 15,000-150,000Da, where the alkyl esters form high MW polymers. A wide range of hydrolytic degradation rates has been found, as monitored by the release of formaldehyde over time. Alkoxy CAs show faster hydrolytic degradation compared to alkyl CAs. Regarding mechanical properties, CAs are classified into primarily viscous (G'>G″) and primarily elastic (G″>G'). Alkoxy CA polymers have a higher loss modulus (G') than storage modulus (G″). Octyl CA polymer possess a G'≈G″ (phase angle ∼45°) providing appropriate balance between mechanical strength and plasticity. Most alkyl CAs are compact and brittle. Alkoxy CAs show enhanced plasticity, but they lack mechanical strength. In general, the Tg for alkoxy CAs is less than alkyl CAs. Alkoxy CAs depolymerise rapidly at temperatures >200°C. Overall, ester sidechains of CA esters strongly affect the polymer property. STATEMENT OF SIGNIFICANCE: Polycyanoacrylates are an important class of biodegradable polymers mainly used as bioadhesives. The study describes comparative evaluation of different cyanoacrylate polymers with respect to their chemistry, degradation, safety, mechanical, and thermal properties. The study forms the basis for choosing appropriate combination of cyanoacrylate esters for various biomedical uses. Moreover, this study reveals properties of a few new polycyanoacrylates for the first time.