Polylactic acid block polymer and preparation method thereof

The invention provides a polylactic acid block polymer and a preparation method thereof. The preparation method comprises the following steps: mixing poly(adipic acid-terephthalic acid)butanediol copolyester, lactide and a first catalyst, and heating to a molten state to react, thereby obtaining the polylactic acid block polymer disclosed as Formula (I). Compared with the polymer obtained by the PLA-PBAT chain extension reaction initiated by diisocyanate in the prior art, the invention uses the molten-state poly(adipic acid-terephthalic acid)butanediol copolyester as the reactant to directly initiate the ring-opening polymerization of lactide, and the polymerization method is mass polymerization without adding the chain extender diisocyanate or any organic solvent, thereby avoiding jeopardizing the human body and environment; the raw materials can be mixed and heated to react to obtain the polylactic acid block polymer, so that the preparation method is simpler and lowers the preparation cost; and the polylactic acid block polymer provided by the invention has definite structure and narrow molecular weight distribution.