Properties of Polycyanoacrylates

Polyalkyl cyanoacrylates are clear, colorless thermoplastics whose physical properties are roughly equivalent to those of other common thermoplastics such as PMMA or polystyrene. Because the majority of adhesives sold today are based on ethyl cyanoacrylate, the properties of polyethyl cyanoacrylate (PECA) will be discussed in detail, and existing data for other esters will be tabulated. 

PECA is soluble in several highly polar solvents including nitromethane, DMF, acetone, tetrahydrofuran, and acetonitrile. Donnelly and Pepper have presented a more complete list of solvents and non solvents for polymethyl, polyethyl, and poly-n-butyl cyanoacrylate. These authors calculated the solubility parameter of PECA to be 11.2. Water absorption by PECA at room temperature and 50% RH is negligible.  

The production of formaldehyde under hydrolytic conditions has been documented. The rate of hydrolysis at pH 8 is two orders of magnitude higher than at pH 7, suggesting that the initial attack on the polymer is by hydroxide ion. Polycyanoacrylates are also susceptible to radiation-induced degradation.  

The thermal instability of polycyanoacrylate is of particular importance both to the manufacturer and the consumer of cyanoacrylate adhesives. The degradation of cyanoacrylate oligomer has been described in general terms previously, as an important step in the production of cyanoacrylate monomer. Heating PECA above 150°C results in the steady production of cyanoacrylate monomer in high yield. This process is end group-initiated 

With the exception of polycyanoacrylates containing reactive groups such as polyallyl cyanoacrylate, the properties of the other polyalkyl cyanoacrylates are generally similar to those of PECA. Table IV presents the data available for commercially important cyanoacrylates. 

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