An ethylene/alpha-olefin copolymer satisfying the following conditions i) to vii): i) density: 0.85 to 0.89 g/cc, measured according to ASTM D-792, ii) molecular weight distribution: 1.5 to 3.0, iii) viscosity: 6,000 cP to 40,000 mPa·s (cP), when measured at a temperature of 180°C, and iv) ReXRc ≤ 1.0 where Re=kee/kec, Rc=kcc/kce, kee represents a propagation reaction rate constant when ethylene is added to a propagation chain of which terminal active site is an ethylene monomer, kec represents a propagation reaction rate constant when an alpha olefin comonomer is added to a propagation chain of which terminal active site is an ethylene monomer, kcc represents a propagation reaction rate constant when an alpha olefin comonomer is added to a propagation chain of which terminal active site is an alpha olefin comonomer, and kce represents a propagation reaction rate constant when an ethylene monomer is added to a propagation chain of which terminal active site is an alpha olefin comonomer; wherein ReXRc is measured as detailed in the description; v) total number of unsaturated functional groups per 1,000 carbon atoms: 0.8 or less, vi) number average molecular weight (Mn): 9,000 to 25,000, and vii) Melt index at 190°C, 2.16 kg load by ASTM D1238: 200 to 1,300 dg/min, wherein the alpha-olefin is comprised in an amount of from greater than 0 to 50 mol% or less, with respect to a total weight of the copolymer. i) density: 0.85 to 0.89 g/cc, measured according to ASTM D-792, ii) molecular weight distribution: 1.5 to 3.0, iii) viscosity: 6,000 cP to 40,000 mPa·s (cP), when measured at a temperature of 180°C, and iv) ReXRc ≤ 1.0 where Re=kee/kec, Rc=kcc/kce, kee represents a propagation reaction rate constant when ethylene is added to a propagation chain of which terminal active site is an ethylene monomer, kec represents a propagation reaction rate constant when an alpha olefin comonomer is added to a propagation chain of which terminal active site is an ethylene monomer, kcc represents a propagation reaction rate constant when an alpha olefin comonomer is added to a propagation chain of which terminal active site is an alpha olefin comonomer, and kce represents a propagation reaction rate constant when an ethylene monomer is added to a propagation chain of which terminal active site is an alpha olefin comonomer; wherein ReXRc is measured as detailed in the description; where Re=kee/kec, Rc=kcc/kce, kee represents a propagation reaction rate constant when ethylene is added to a propagation chain of which terminal active site is an ethylene monomer, kec represents a propagation reaction rate constant when an alpha olefin comonomer is added to a propagation chain of which terminal active site is an ethylene monomer, kcc represents a propagation reaction rate constant when an alpha olefin comonomer is added to a propagation chain of which terminal active site is an alpha olefin comonomer, and kce represents a propagation reaction rate constant when an ethylene monomer is added to a propagation chain of which terminal active site is an alpha olefin comonomer; wherein ReXRc is measured as detailed in the description; v) total number of unsaturated functional groups per 1,000 carbon atoms: 0.8 or less, vi) number average molecular weight (Mn): 9,000 to 25,000, and vii) Melt index at 190°C, 2.16 kg load by ASTM D1238: 200 to 1,300 dg/min,