Transparent thermoplastic resin and method for preparing the same

1. A transparent thermoplastic resin comprising:

a rubber phase including an aromatic rubbery block copolymer resin comprising about 10 to about 50% by weight of a rubbery polymer and about 50 to about 90% by weight of an aromatic vinyl compound; and

a resin phase including a terpolymer comprising about 50 to about 95% by weight of an aromatic vinyl compound, about 0.1 to about 30% by weight of a vinyl cyanide compound and about 0.1 to about 45% by weight of an unsaturated alkyl ester compound,

wherein said rubber phase and said resin phase have a co-continuous phase structure and wherein the difference between refractive indices of said terpolymer and said aromatic rubbery block copolymer resin is about 0.008 or less.

2. The transparent thermoplastic resin of claim 1 , wherein a part of said rubber phase and a part of said resin phase form a discontinuous structure.

3. The transparent thermoplastic resin of claim 1 , comprising said rubber phase in an amount of about 20 to about 80% by weight, and said resin phase in an amount of about 20 to about 80% by weight.

4. The transparent thermoplastic resin of claim 1 , wherein said terpolymer has weight average molecular weight of about 140,000 to about 350,000.

5. The transparent thermoplastic resin of claim 1 , wherein:

said aromatic vinyl compound includes styrene, C1-C8 alkyl substituted styrene, vinyl naphthalene, vinyl toluene or a combination thereof; said vinyl cyanide compound includes acrylonitrile, methacrylonitrile, ethacrylonitrile, or a combination thereof; and said unsaturated alkyl ester compound includes C1-C12 alkyl substituted (meth)acrylate or a combination thereof.

6. The transparent thermoplastic resin of claim 1 , wherein said rubbery polymer is a diene-based rubber.

7. The transparent thermoplastic resin of claim 1 , further comprising an additive selected from the group consisting of flame retardants, antibiotic agents, releasing agents, thermal stabilizers, antioxidants, light stabilizers, compatibilizers, dyes, inorganic fillers, surfactants, nucleating agents, coupling agents, fillers, plasticizers, impact modifiers, admixing agents, coloring agents, stabilizers, lubricants, antistatic agents, pigments, flameproof agents, and combinations thereof.

8. A method for preparing a transparent thermoplastic resin, the method comprising:

preparing an aromatic rubbery block copolymer resin comprising about 10 to about 50% by weight of a rubbery polymer and about 50 to about 90% by weight of an aromatic vinyl compound;

preparing an aromatic vinyl-vinyl cyanide-unsaturated alkyl ester terpolymer having a weight average molecular weight of from about 140,000 to about 350,000 by polymerizing about 50 to about 95% by weight of an aromatic vinyl compound, about 0.1 to about 30% by weight of a vinyl cyanide compound and about 0.1 to about 45% by weight of an unsaturated alkyl ester compound to have a refractive index difference between the terpolymer and the aromatic rubbery block copolymer resin of about 0.008 or less; and

mixing and melt-extruding the aromatic rubbery block copolymer resin and the aromatic vinyl-vinyl cyanide-unsaturated alkyl ester terpolymer to prepare a transparent thermoplastic resin comprising a rubber phase comprising said aromatic rubbery block copolymer resin and a resin phase comprising said terpolymer, wherein said rubber phase and said resin phase have a co-continuous phase structure and wherein the difference between refractive indices of said terpolymer and said aromatic rubbery block copolymer resin is about 0.008 or less.

9. The method of claim 8 , comprising mixing and melt extruding about 20 to about 80% by weight of said aromatic rubbery block copolymer and about 20 to about 80% by weight of said aromatic vinyl-vinyl cyanide-unsaturated alkyl ester terpolymer.