Graft copolymer for transparent thermoplastic polyurethane resin, preparation method thereof, and polyurethane resin composition containing the same

A method for preparing a graft copolymer for transparent thermoplastic polyurethane resin comprising the following steps:

• a) preparing rubber latex having multi-layered structure in which the refraction index of an inner layer is higher than that of an outer layer by the processes of
• i) preparing the inner layer of rubber latex by emulsion polymerization of 25-75 weight % of the total monomer mixture composed of a conjugated diene monomer, an ethylenically unsaturated aromatic compound and a cross-linking agent;
• and
• ii) preparing the outer layer of rubber latex by emulsion polymerization of the prepared inner layer after adding the remaining 25-75 weight % of the monomer mixture thereto;
• and
• b) preparing thermoplastic graft copolymer by graft polymerization in one-step or multi-step of 50-85 weight % of the rubber latex having multi-layered structure and 15-50 weight % of a C2-C20 vinyl monomer.