Propylamine terminated polymethylsiloxanes were synthesized by the reaction of bis (paminopropyl) tetramethyldisiloxane with octamethylcyclotetrasiloxane at 80℃, and bis (p-chloroformyl phenylene) terephthalates were synthesized from bis (p-carbetoxy phenylene) terephthalate produced by the reaction of terephthaloylchloride with ethyl-p-hydroxybenzoate in the solution of tetrachloroethane. Poly(dimethylsiloxane-arylester) block copolymers were prepared through the copolymerization of propyl amine terminated polydimethylsiloxane with bis (p-chloroformyl phenylene) tereptthalate in the solution of tetrachloroethane and tetraethylammoniumchloride. The identification of the products were made by IR and NMR spectra. The block copolymer was yellowish solid and depolymerization activation energies were calculated by dynamic and isothermal TGA data. The depolymerization activation energies for the copolymer containing 40 mole% siloxane unit were 48.35 Kcal from dydamic TGA and 61.65 Kcal from isothermal TGA measurement.