Many applications of plastic materials, especially transparent materials, involve prolonged exposure to ultraviolet (UV) radiation, which can damage or discolor the plastic. A large number of ultraviolet radiation absorbing additives are available, but it is well-known that such additives lose their effectiveness over time because of leaching or because of migration to the plastic surface.
To avoid this loss of effectiveness, UV radiation absorbers which are capable of being copolymerized into the polymer matrix have been developed. Such materials offer the obvious advantage of being incapable of either leaching or blooming, and, thus, maintain their protective function. Efforts to date to synthesize such copolymerizable UV absorbers have focused on ethylenically-unsaturated molecules, often acrylate-functional molecules, which are easily incorporated into acrylate or polyolefin polymers.
Common core molecules which have received wide-spread attention are esters of 2-cyano-3,3-diaryl acrylic acid, the so-called cyanoacrylates. U.S. Pat. Nos. 4,218,392; 4,202,834; and 4,129,667; (assigned to GAF Corp.) describe acrylate-functional cyanoacrylates. The cyanoacrylates described in these patents feature acrylate groups at, the terminus of the acrylate ester chain which are easily copolymerized with ethylenically-unsaturated monomers such as methyl methacrylate, polyvinyl chloride and polyethylene. A common intermediate in the preparation of the GAF cyanoacrylates is 2-hydroxyethyl 2-cyano-3,3-diphenylacrylate, a monohydroxylate cyanoacrylate.
Patents granted to General Electric Co. (U.S. Pat. Nos. 4,366,207; 4,264,719; 4,260,680; and 4,247,475) describe cyanoacrylate-type UV radiation absorbers which are incorporated into polycarbonate polymers via aromatic phenolic hydroxyl groups. Similarly, U.S. Pat. Nos. 4,555,559 and 4,555,545 (Toshiba Silicone Co.) describe phenolic-functional cyanoacrylates used as stabilizers for polycarbonate resins. U.S. Patent No. 4,576,870 (Rohm GmbH) describes a number of methods of stabilizing polycarbonate resins, including the use of acrylate-functional cyanoacrylates. None of the aforementioned references reveal a means of stabilizing polyurethane or polyester polymers produced by step-growth type polymerizations.
U.S. Pat. No. 4,378,194 (General Motors Corp.) describes urethane paints stabilized against UV radiation by copolymerization of hindered piperidinols into the urethane polymer chain. U.S. Pat. Nos. 4,831,109 and 4,691,059, assigned to the assignee of the present application, both of which are incorporated by reference herein, describe 2-hydroxybenzophenone UV radiation stabilizers for polyurethanes, polyesters and polycarbonates in which two or more aliphatic hydroxyl groups are part of an aliphatic chain pendant from one of the aromatic nuclei. Cyanoacrylate UV radiation absorbers are not disclosed in any of these three patents. U.S. Pat. No. 5,096,781 (Ciba-Geigy Corp.) discloses unspecified cyanoacrylate-type UV radiation absorbers having at least one quaternary nitrogen moiety in the molecule to impart solubility in water and optionally having from 1 to 3 aliphatic hydroxyl groups in the acrylate ester side chain.