Chain polymerization alkyl-2-cyanoacrylates

A brief description of the chemistry of these materials is described on the article entitled Alkyl-2-cyanoacrylates. Commercial adhesive products are usually based on the ethyl ester but methyl, n-butyl, allyl -methoxyethyl and -ethoxyethyl are also important. Formulated adhesives consist of essentially pure monomer with relatively small amounts of property-modifying additives. The curing reaction is anionic polymerization, initiated by traces of alkaline material present on most substrate surfaces, particularly in conjunction with low levels of surface moisture (see Chain polymerization). 

The rate of degradation of PCAs is much faster than PLGAs which do not necessitate the overloading of the body with excess polymer that is still present long after initial treatment (Lherm et al. 1992). The alkyl cyanoacetate that is formed and the rate of formation are dependent on the length of the alkyl chain of the monomer used to produce the microparticles. The degree of toxicity is also dependent on the length of the alkyl chain. Poly(cyanoacrylates) have been approved by the FDA in several systems, so it is one of the more acceptable of the polymeric systems. 

Tissue adhesives are formulated from cyanoacrylate compounds such as bucrylate, enbucrilate, or mecry-late which polymerize in an exothermic reaction on contact with a fluid or basic substance to form a strong, flexible, and waterproof bond. They are synthesized by reacting formaldehyde with alkyl cyanoacetate to obtain a prepolymer, which may be depolarized to a liquid monomer by heat. This monomer may then be modified by altering the alkoxycarbonyl (-COOR) group of the molecule to give compounds of different chain lengths. 

The loss of the addition ability of an ion by delocalization of the electron defect in a conjugated polyene chain is documented by the observation of Subramanian et al. They polymerized monomers with C=C and C=N bonds by electroinitiation. Anionic polymerization of phenylacetylene started very easily but it rapidly died out without any external cause [109]. The polymerization of -alkyl-2-cyanoacrylate in the presence of tetracyanoethy-lene yields only low-molecular-weight products. This is due to the formation... 

Polyalkylcyanoacrylates (PACA) are considered interesting polymers because of the high reactivity of the corresponding monomer, which can polymerize in various media, and also in water. In particular, monomers are cyanoacrylate esters where alkyl chain length varies from methyl to decyl (Fig. 1.26). 

FIGURE 8.2 Cyanoacrylate monomer units polymerize in a join by an anionic mechanism, typically initiated by hydroxyl groups in adsorbed water. The alkyl (-R) group can be varied to modify the polymer properties. R may be methyl, ethyl or butyl, or contain an unsaturated group allowing cross-linking between chains and thus greater stability. 

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