Alkyl, 2-cyanoacrylate

In order to become useful dmg delivery devices, biodegradable polymers must be formable into desired shapes of appropriate size, have adequate dimensional stability and appropriate strength-loss characteristics, be completely biodegradable, and be sterilizahle (70). The polymers most often studied for biodegradable dmg delivery applications are carboxylic acid derivatives such as polyamides poly(a-hydroxy acids) such as poly(lactic acid) [26100-51-6] and poly(glycolic acid) [26124-68-5], cross-linked polyesters poly(orthoesters) poly anhydrides and poly(alkyl 2-cyanoacrylates). The relative stabiUty of hydrolytically labile linkages ia these polymers (70) is as follows ... 

The alkyl 2-cyanoacrylates have become well-known adhesives, often popularly known as super-glue. 

McGee WA, Oglesby FI, Raleigh RI, Fassett DW The determination of a sensory response to alkyl 2-cyanoacrylate vapor in air. Am Ind Hyg Assoc J29 SS S6, 1968... 

Alkyl-2-cyanoacrylates are readily polymerized in the presence of weak bases such as water. Because of the presence of the strong polar cyano pendant group these polymers (e.g. Super Glue) are excellent adhesives. Polybutyl-2-cyanoacrylate is tolerated by the body better than its lower alkyl homo-logues. Hence polybutyl-2-cyanoacrylate is used as an adhesive aid to stop bleeding in some surgical operations. 

Ihe polymers of the 2-cyanoacrylic esters, more commonly known as the alkyl 2-cyanoacrylates, are hard glassy resins that exhibit excellent adhesion to a wide variety of materials. The polymers are spontaneously formed when their liquid precursors or monomers are placed between two closely fitting surfaces. Tile spontaneous polymerization of these very reactive liquids and the excellent adhesion properties of the cured resins combine to make these compounds a unique class of single-component, ambient-temperature-curing adhesive of great versatility (Table 3). The materials that can be bonded run the gamut from metals, plastics, most elastomers, fabrics, and woods to many ceramics. 

By reaction with covalent organic bases (Et3N, Me2PhN, pyridine) N-alkyl-2-cyanoacrylates can be transformed to zwitterions of the type... 

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... 

Cyanoacrylate adhesives were introduced in 1958 by Easttnan Kodak. They are based on alkyl-2-cyanoacrylate monomers. 

Alkyl-2-cyanoacrylates can be prepared by several synthetic procedures. The only method of importance involves the Knoevenagel condensation of an alkylcyanoacetate with formaldehyde. As this is a base-catalysed reaction, the monomer is rapidly polymerized to give a low-molecular-weight poly(alkyl-2-cyanoacrylate). The resulting polymer is retropolymer-ized by heating under controlled conditions to yield monomeric cyanoacrylate (Scheme 1). 

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). 

Plasticizers These are required to reduce the inherent brittleness of poly(alkyl-2-cyanoacrylates). This can be achieved by using non-copolymerizing plasticizers such as esters or higher alkyl cyanoacrylates, which copolymerize with the basic adhesive monomer. Toughness properties can be improved by the inclusion of rubber toughening materials such as ABS (acrylonitrile-butadiene-styrene) or MBS (methacrylate-butadiene-styrene) copolymers. Whichever approach is adopted, toughness is only achieved at the expense of reduced cure speed. 

Alkyl-2 cyanoacrylates J GUTHRIE Monomer synthesis polymerization... 

Fig. 6. The molecular structure of cyanoacrylates where the structure of the side chain (R) defines the different alkyl 2-cyanoacrylates...

PACA are hard glassy polymers with a high polarity , and this explains their adhesive properties (Coover et al., 1959). The adhesive action of alkyl 2-cyanoacrylates was discovered during an investigation of a series of polymers derived from 1,1-disubstituted ethylenes. It was found that certain compounds of general structure ... 

Donelly, E.F., Johnston, D.S. and Pepper, D.C. (1977) Ionic and zwitterionic polymerisation of n-alkyl 2-cyanoacrylates. Polymer lett., 15, 399-405. 

Tbe lower esters of alkyl 2-cyanoacrylates (eg, methyl, ethyl esters) provide adhesives with excellent lap-shear strengths to a variety of different substrates (3). They are, however, brittle materials and generally require the addition of a rubber-toughening agent to improve peel strength and impact resistance (4). The low esters have pungent odors whereas the higher esters, in particular the alkoxyalkyl esters, are virtually odorless (3). 

There are some examples of the use of so-called photobase generators in the preparation of polymers by anionic means. Photobase generators are compounds that produce bases upon irradiation with light, examples include cobalt complexes 0-acyloximines and benzyloxycarbonyl derivatives. PBGs are generally important in polymer science due to their application in photoinitiated transformation of polymeric materials and epoxy resins. Kutal et al. have reported the anionic polymerization of alkyl 2-cyanoacrylates initiated by anionic species upon the irradiation of group 8 metallocenes [YAM 98, YAM 99, YAM 00, SAN 02, BRI 02, DIN 03, SAN 05,... 

BRI 02] Brinkmann N.R., Schaefer H.F., Sanderson C.T. et al, Can the radical anion of alkyl-2-cyanoacrylates initiate anionic polymerization of These instant adhesive monomers , Journal of Physical Chemistry A, vol. 106, pp. 847-853, 2002. 

The disadvantages of its use (polymer hydrolisis, with formation of toxic products) became obvious, so that higher alkyl 2-cyanoacrylates (ethyl-2-cyano-acrylate, propyl-2-cyanoacrylate, and 1-butyl-2-cyanoacrylate) have been tried, and finally octyl-2-cyanoacrylate or fluorurated cyanoacrylates. 

Beech, D. R., Bonding of alkyl-2-cyanoacrylates to human dentine and enamel, J. Dent. Res., 51, 1438, 1972. 

The poly (alkyl 2-cyanoacrylates) are used as biodegradable tissue adhesives in... 

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