Other Adhesive Properties and Modifiers

The first examples of thickened cyanoacrylate adhesives were described by Coover and Shearer in a U.S. Patent. The thickeners cited and claimed were polyalkyl cyanoacrylates, polyacrylates, polymethacrylates, cellulose nitrate, and cellulose organic acid esters, such as cellulose acetate butyrate. Several years later. Wicker and Shearer improved the process for thickening cyanoacrylates. Instead of adding the thickener directly to the monomer, the thickener was first dissolved in a volatile solvent and then added to the ester. The solvent was then vacuum stripped to give the thickened adhesive. The authors claimed that this process gave adhesives having better clarity, better storage stability, and faster cure speed than adhesives prepared by the older method. 

Copolymers of acrylonitrile and lower acrylates have also been used as thickeners. The proportion of the acrylate in the copolymer was 60-90% by weight the preferred acrylates were the methyl through butyl esters. These authors also tested an extensive list of known and novel thickeners as comparative examples. The latter included nitrile rubber and vinyl acetate-vinyl chloride, methyl methacrylate-butadiene-styrene (MBS), and acrylonitrile-butadiene-styrene (ABS) copolymers. The copolymers of this invention were claimed to provide better stability, higher viscosity, less stringing, and better impact strength than do the thickeners of the prior art. The claims of this patent do not cover the disclosed copolymers. Polyvinyl ethers are another class of cyanoacrylate thickeners which have been disclosed but not claimed.  

Several other examples of copolymeric thickeners can be found in the literature. For instance, copolymers of 20-80% methyl methacrylate and 80-20% acrylonitrile have been disclosed as thickeners for a dental cyanoacrylate adhesive. Recently, adhesives containing a plasticizer and a vinyl chloride-vinyl acetate copolymer were patented as additives for cyanoacrylate adhesives. The copolymers contained 10-20% vinyl acetate and less than 2% maleic acid. These polymers were not claimed as thickeners 

Copolymers of alkyl cyanoacrylates and styrene or methylstyrene also have been patented as thickeners for cyanoacrylates.These copolymers were said to have better solubility in cyanoacrylates than the cyanoacrylate homopolymers. The authors showed that polystyrene-co-methyl cyanoacrylate is soluble in ethyl cyanoacrylate but that polymethyl cyanoacrylate is not. 

Cyanoacrylates have been recognized as potential surgical adhesives due to their cure properties and their biodegradability. Viscosity control is very important in this application, and the thickeners used must meet the additional requirements of biodegradability and biocompatibility. One polymer that does have these attributes is polylactic acid (30). This polymer 

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