Copolymer of ethylene and alpha-olefin, and method for preparing same

A method for preparing a liquid random copolymer of ethylene and alpha-olefin, comprising a step of:

• carrying out solution polymerization of ethylene and alpha-olefin having 3 to 20 carbon atoms, under a catalyst system containing:
• (A) a bridged metallocene compound represented by following Formula 1, and
• (B) at least one compound selected from a group consisting of (i) an organoaluminum oxy-compound and (ii) a compound which reacts with the bridged metallocene compound to form ion pair,
• wherein, R1 and R4 are hydrogen atom;
• R2, R3, R5, R8, R9 and R12 are independently hydrogen atom, hydrocarbon group or silicon-containing hydrocarbon group, and adjacent groups can be connected to form a ring structure at least one of R2 and R3 is hydrocarbon group having 4 or more carbon atoms;
• R6 and R11 are the same as each other and are hydrogen atom, hydrocarbon group or silicon-containing hydrocarbon group R7 and R10 are the same as each other and are hydrogen atom, hydrocarbon group or silicon-containing hydrocarbon group;
• R6 and R7 can be connected to hydrocarbon having 2 to 3 carbon atoms to form a ring structure R11 and R10 can be connected to hydrocarbon having 2 to 3 carbon atoms to form a ring structure;
• R6, R7, R10 and R11 are not hydrogen atom at the same time;
• Y is carbon atom or silicon atom;
• R13 and R14 are independently aryl group;
• M is Ti, Zr or Hf;
• Q is independently halogen, hydrocarbon group, anionic ligands or a neutral ligand which can be coordinated to a lone pair of electrons;
• j is an integer of 1-4;
• and
• wherein the liquid random copolymer (1) comprises 40 to 60 mol % of ethylene units and 60 to 40 mol % of alpha-olefin units having 3 to 20 carbon atoms;
• (2) has a number average molecular weight (Mn) of 500 to 10,000 and a molecular weight distribution (Mw/Mn wherein Mw is weight average molecular weight) of 3 or less measured by gel permeation chromatography (GPC);
• (3) has a kinematic viscosity at 100° C. of 30 to 5,000;
• (4) has a pour point of 30 to −45° C., and (5) has a bromine number of 0.1 or less.