A copolymer deposited with particles of catalytic metal is disclosed in the present invention, which is formed from an ethylenically unsaturated monomer and a hydrophilic monomer, and the catalytic metal is Au, Ag, Pd, Pt or Ru. The copolymer is hydrophilic when the temperature is lower than a specific temperature, and will become hydrophobic when the temperature is greater than the specific temperature. The present invention also discloses a method for forming a metal layer on a substrate via electroless plating, which includes contacting the substrate with an ink composition, drying the ink composition on the substrate, and contacting the dried ink composition with an electroless plating solution, wherein the ink composition contains the copolymer of the present invention in an aqueous phase. The present invention further discloses a method for forming metal conductors in through holes of a substrate.