Branched (meth)acrylate copolymer with high refractive index and method for preparing the same

1. A branched (meth)acrylate copolymer prepared by polymerizing a monomer mixture comprising (A) about 20 to less than about 99.999% by weight of a (meth)acrylate monomer having a refractive index higher than methyl methacrylate, wherein said (meth)acrylate monomer having a refractive index higher than methyl methacrylate (A) has a refractive index of more than about 1.49 but not more than about 1.59; (B) greater than about 0 to about 79.999% by weight of a mono-functional unsaturated monomer comprising a C1-C8 alkyl methacrylate; C1-C8 alkyl acrylate; acid anhydride monomer; (meth)acrylamide monomer; unsaturated nitrile monomer; allyl glycidyl ether; glycidyl methacrylate; aromatic vinyl monomer; or a combination thereof; and (C) about 0.001 to about 10% by weight of a crosslinking monomer comprising a silane compound; siloxane compound; aromatic crosslinking monomer; vinyl group-containing monomer; allyl compound; or a combination thereof, wherein the weight average molecular weight of the branched (meth)acrylate copolymer is from about 500,000 to about 5,000,000.

2. The branched (meth)acrylate copolymer of claim 1 , wherein said (meth)acrylate monomer having a refractive index higher than methyl methacrylate (A) comprises an aromatic methacrylate, an aliphatic methacrylate, or a combination thereof represented by the following Chemical Formula 1, Chemical Formula 2, or a combination thereof:

wherein m is an integer from 0 to 10, and X comprises a cyclohexy group, a phenyl group, a methylphenyl group, a methylethylphenyl group, a propylphenyl group, a methoxyphenyl group, a cyclohexylphenyl group, a chlorophenyl group, a bromophenyl group, a phenylphenyl group, or a benzylphenyl group;

wherein m is an integer from 0 to 10, Y is oxygen (O) or sulfur (S), and Ar comprises a cyclohexyl group, a phenyl group, a methylphenyl group, a methylethylphenyl group, a methoxyphenyl group, a cyclohexylphenyl group, a chlorophenyl group, a bromophenyl group, a phenylphenyl group, or a benzylphenyl group.

3. The branched (meth)acrylate copolymer of claim 2 , wherein said aromatic or aliphatic methacrylate comprises 2-ethylphenoxy methacrylate, 2-ethylthiophenyl methacrylate, phenyl methacrylate, phenoxyethyl methacrylate, benzyl methacrylate, 2-phenylethyl methacrylate, 3-phenylpropyl methacrylate, 4-phenylbutyl methacrylate, 2-2-methylphenylethyl methacrylate, 2-3-methylphenylethyl methacrylate, 2-4-methylphenylethyl methacrylate, 2-(4-propylphenyl)ethyl methacrylate, 2-(4-(1-methylethyl)phenyl)ethyl methacrylate, 2-(4-methoxyphenyl)ethylmethacrylate, 2-(4-cyclohexylphenyl)ethyl methacrylate, 2-(2-chlorophenyl)ethyl methacrylate, 2-(3-chlorophenyl)ethyl methacrylate, 2-(4-chlorophenyl)ethyl methacrylate, 2-(4-bromophenyl)ethyl methacrylate, 2-(3-phenylphenyl)ethyl methacrylate, 2-(4-benzylphenyl)ethyl methacrylate, or a combination thereof.

4. The branched (meth)acrylate copolymer of claim 1 , wherein C1-C8 alkyl methacrylate comprises methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate or a combination thereof said C1-C8 alkyl acrylate comprises methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, 2-ethyl hexyl acrylate, or a combination thereof; said acid anhydride monomer comprises maleic anhydride; said (meth)acrylamide monomer comprises acrylamide, methacrylamide, or a combination thereof said unsaturated nitrile monomer comprises acrylonitrile, methacrylonitrile, or a combination thereof and said aromatic vinyl monomer comprises styrene, α-methyl styrene, or a combination thereof.

5. The branched (meth)acrylate copolymer of claim 1 , wherein said silane or siloxane compound comprises an unsaturated hydrocarbon group-containing silicone-containing crosslinking monomer; said aromatic crosslinking monomer comprises divinylbenzene; said vinyl group-containing monomer comprises 1,4-divinyloxybutane, divinylsulfone, or a combination thereof; and said allyl compound comprises diallyl phthalate, diallylacrylamide, triallyl (iso)cyanurate, triallyl trimelitate, or a combination thereof.

6. The branched (meth)acrylate copolymer of claim 1 , wherein said silane or siloxane compounds is represented by the following Chemical Formula 3 or Chemical Formula 4 or a combination thereof:

wherein R1, R2, R3, R4, R5 and R6 may be the same or different and are independently hydrogen, a C1-5 linear or branched alkyl group, a C3-30 cycloaliphatic hydrocarbon group, a C6-10 aryl group, or a C2-12 unsaturated hydrocarbon group, x is 1 to 20 and y is 1 to 20.

7. The branched (meth)acrylate copolymer of claim 6 , wherein at least two of R1, R2, R3, R4, R5 and R6 are C2-12 unsaturated hydrocarbon groups.

8. The branched (meth)acrylate copolymer of claim 6 , wherein said x+y is 2 to 40.

9. The branched (meth)acrylate copolymer of claim 1 , wherein the monomer mixture comprises (A) about 20 to about 99% by weight of a (meth)acrylate monomer having a refractive index higher than methyl methacrylate.