METHOD FOR PRODUCING PROPYLENE-BASED BLOCK COPOLYMER

PROBLEM TO BE SOLVED: To provide a method for efficiently producing a propylene-based block copolymer excellent as a moldability improver, capable of controlling physical properties by added to general purpose resin components as a third component and improving molded product externals by using the property-controlled copolymer. SOLUTION: The method for producing a propylene-based block copolymer comprises at least two steps, that is, producing a specific crystalline propylene copolymer part in a former polymerization step (A) and producing a specific propylene-ethylene random copolymer part in a latter polymerization step (B), wherein the former polymerization step (A) comprises feeding hydrogen and propylene in a reactor, polymerizing propylene in the presence of a catalyst by decreasing hydrogen concentration to propylene with time and, when the crystalline propylene polymer is obtained, keeping the gas concentration ratio (H2/C3) of hydrogen to propylene in the unreacted gas at a specific value. COPYRIGHT: (C)2008,JPO&INPIT