Methods for inhibiting the polymerization of methacrylate monomers

#The present invention relates to methods for inhibiting the polymerization of methacrylate monomers. More particularly, the present invention relates to a method for inhibiting polymerization of (meth)acrylate monomers during processing and storage of monomer mixtures used in the dental, audiological, medical, and cosmetic fields by using an effective amount of alpha-tocopherol (Vitamin E).

#Polymerizable methacrylate monomers undesirably spontaneously react during various stages of the manufacture, processing, handling, storage and use thereof. It is well known that methacrylate monomers readily polymerize during storage and that such polymerization increases with concurrent temperature increases. Utilization of meth(acrylate) monomers in the dental restorative field involving denture manufacture or in the audiological field of hearing aid shell manufacture requires stability of the monomer mixtures until the operator desires polymerization to ensue. In the field of cosmetic materials, creation of an artificial human nail structure requires that a coating that can be easily applied, polymerizes readily and rapidly due to controlled initiation. U.S. Pat. No. 6,080,389 to Sheariss et al, and U.S. Pat. No. 5,830,442 issued to Beaver describe artificial human nails. To reduce the chance of uncontrolled initiation of polymerization, methacrylate monomers are frequently treated with polymerization inhibitors. Methacrylate monomers are treated with a variety of polymerization inhibitors such as hydroquinone (HQ), methyl ether of hydroquinone (MeHQ), sterically hindered hydrophenols such as 2,6-di-tert-butyl-4-methylphenol (also known as butylated hydroxytoluene, BHT), and sterically hindered quinones such as di-tert-butylhydroquinone.

#U.S. Pat. No. 5,461,124 (“'124 patent”) discloses the use of Vitamin E as an inhibitor against premature polymerization in reactive systems capable of undergoing a free radical initiated polymerization which system before and/or after polymerization thereof are placed in tissue contact with a living body. The '124 patent is dealing with methyl methacrylate and poly(methylmethacrylate) of bone cements. The reactive composition of the '124 patent is monocomponent or multicomponent medical and/or dental-medical adhesives, cements, or fillers based on conventional monofunctional and/or polyfunctional olefinically unsaturated compounds, particularly acrylic acid and or methacrylic acids or derivatives thereof.

#Testing was performed to demonstrate the effectiveness of the present invention at inhibiting the polymerization of (meth)acrylate monomers. Tests were conducted in sealed brown glass bottles filled with ethyl methacrylate and various inhibitors. The bottles were placed in a 75° C. water bath in the dark and checked daily for polymer. The monomers remained liquid until they polymerized to a solid. 1 TABLE 1 Stability Data Days to Polymerization Vitamin E in EMA storage at 75° C. Vitamin E (ppm) 102 29 205 40 410 54 MeHQ (ppm) 15 15 95 56 BHT (ppm) 208 29

#MeHQ is the Methyl ether of Hydroquinone and BHT is butylated hydroxytoluene. From this data it can be concluded that all additives tested (Vitamin E, MeHQ and BHT) provide some stability to the Ethyl Methacrylate liquid. The more inhibitor added to the ethyl methacrylate, the longer the liquid maintains stability. Comparatively speaking, the Vitamin E is approximately twice as powerful an inhibitor as BHT and MeHQ is four times a better inhibitor as Vitamin E.

#Using the accepted convention that raising the temperature 10° C. doubles the rates of reaction, the above data in comparative form at room temperature yields the following room temperature stability expectations. 2 TABLE 2 Expected Stability Vitamin E stabilized EMA storage at 25° C. Days to Polymerization Vitamin E (ppm) 102 938 205 1,280 410 1,728 MeHQ (ppm) 15 480 95 1,792 BHT (ppm) 208 928