this invention relates to a method of polymerization of lactide or glycolide monomers and in particular to a method of polymerizing one type of the monomers or two types of the monomers using alkyl aluminum catalyst to proceed with bulk or solution polymerization to prepare biodegradable homopolymers or copolymers , and high - molecular - weight homopolymers of polylactide , polyglycolide , or copolymers of lactide / glycolide prepared thereof .