Hydrophilic copolymer of N,N-(C.sub.1 -C.sub.2 alkyl) acrylamide

A contact lens formed from a hydrogel consisting essentially of an aqueous solution and a copolymer formed from about:

• ______________________________________ 48-49% N,N-dimethyl acrylamide 40-50% Methyl methacrylate 1-10% C.sub.1 -C.sub.4 alkyl acrylate 1-2% Ethylene glycol dimethacrylate. ______________________________________ -18. A contact lens formed from a hydrogel consisting essentially of an aqueous solution and a copolymer formed from about:
• ______________________________________ 48-49% N,N-dimethyl acrylamide 50% Methyl methacrylate 1-2% Ethylene glycol dimethacrylate. ______________________________________ -19. A contact lens formed from a hydrogel comprising an aqueous solution and a hydrophilic copolymer of N,N-dimethyl acrylamide, said contact lens being optically clear and having a thickness of from about 0.02 to about
• 0.1 millimeters. 20. A contact lens formed from a copolymer of N,N-dimethyl acrylamide, said copolymer having the following physical properties:
• A. in the dry state:
• 1. compressive stress-strain values measured on cylinders 0.35-0.40 inches thick and 0.45-0.65 inches in diameter at crosshead rates between 20% and 60% of the initial sample thickness per minute including:
• a. a modulus before yield of over about 150,000 psi;
• b. compressability to at least about 60% relative to the initial sample thickness without sample failure;
• c. compressive strength at 60% compressability of above about 40,000 psi;
• 2. a hardness on the Shore D scale of above about 75 durometers.
• B. in the hydrated state:
• 1. compressive stress-strain values measured under water on cylinders 0.4-0.5 inches thick and 0.4-0.7 inches in diameter at crosshead rates of 20% of the initial sample thickness per minute including:
• a. a compressive strength after cycling twice to 40% of over about 400 psi;
• b. compressability to at least about 60% relative to the initial sample thickness without sample failure;
• c. a secant modulus at 25% compression in a third compression of between about 120 and 350 psi, and at 40% compression in a third compression between 150 and about 500 psi;
• 2. a hardness on the Shore 00 scale from about 70 to about 87 durometers.
• . A process for forming a hydrogel comprising:
• a. forming a reaction mixture consisting essentially of from about 20 to about 80 weight percent N,N-(C.sub.1 -C.sub.2 alkyl) acrylamide, from about 80 to about 20 weight percent of at least one C.sub.1 -C.sub.4 acrylate or methacrylate ester, and from about 0.05 to about 4 weight percent of a multiester of acrylic or methacrylic acid;
• b. adding a polymerization initiator to said reaction mixture;
• c. maintaining said reaction mixture and initiator at a temperature sufficient to cause copolymerization of said reaction mixture until a cross-linked, hydrophilic, copolymer is obtained which has structural integrity;
• and,
• d. equilibrating said copolymer reaction product with an aqueous solution.
• 2. A process of claim 21 wherein said initiator comprises a low
• temperature initiator. 23. A process of claim 22 wherein said low
• temperature initiator comprises diisopropyl peroxydicarbonate. 24. A process of claim 23 wherein said diisopropyl peroxydicarbonate is present in an amount of from about 0.05 to about 0.5 weight percent based on the
• weight of said comonomers. 25. A process of claim 24 wherein said
• polymerization is a bulk polymerization. 26. A process of claim 21 wherein
• said reaction mixture also contains a hydroxylic solvent. 27. A process of claim 26 wherein said solvent consists essentially of tertiary butanol.
• A process of claim 27 wherein said reaction mixture contains from about 5 to about 60 weight percent of a C.sub.1 -C.sub.4 alkyl
• methacrylate. 29. A process of claim 28 wherein said C.sub.1 -C.sub.4
• alkyl methacrylate comprises methyl methacrylate. 30. A hydrogel prepared
• according to the process of claim 29. 31. A contact lens formed from the hydrogel of claim 30.