Abstract: A polyester copolymer has two types of ester bond-forming monomer residues as main structural units when the two types of ester bond-forming monomers are defined as “monomer A” and “monomer B”, respectively, the polyester copolymer satisfies (1) and (2): (1) an R value represented by equation: R value=[AB]/(2[A][B])×100 [A]: mole fraction of monomer A residues in the polyester copolymer [% by mol], [B]: mole fraction of monomer B residues in the polyester copolymer [% by mol], and [AB]: mole fraction of a structure in which the monomer A residues and the monomer B residues are adjacent to each other (A-B and B-A) in the polyester copolymer [% by mol], is 0.45 or more and 0.99 or less; and (2) a crystallization rate of at least one of the monomer A residues and the monomer B residues is less than 14%.

Abstract: A biodegradable block copolymer has high conformability and excellent degradability. The block copolymer including a polyalkylene glycol block and a polyhydroxyalkanoic acid block, wherein the mass ratio of the polyalkylene glycol block with respect to the total mass is 10 to 60%; the carbonyl carbon has a carbon nuclear relaxation time T1? of not more than 20 ms; and the block copolymer satisfies Equation (1): ?=?1×?2>20 (1) ?1: crystallization rate of the polyalkylene glycol block; ?2: crystallization rate of a poly-A block, wherein A represents, among the repeat units contained in the polyhydroxyalkanoic acid block, a repeat unit whose homopolymer composed of the same repeat units has a highest crystallization rate.

Abstract: A polyester copolymer has two types of ester bond-forming monomer residues as main structural units when the two types of ester bond-forming monomers are defined as “monomer A” and “monomer B”, respectively, the polyester copolymer satisfies (1) and (2): (1) an R value represented by equation: R value=[AB]/(2[A][B])×100 [A]: mole fraction of monomer A residues in the polyester copolymer [% by mol], [B]: mole fraction of monomer B residues in the polyester copolymer [% by mol], and [AB]: mole fraction of a structure in which the monomer A residues and the monomer B residues are adjacent to each other (A-B and B-A) in the polyester copolymer [% by mol], is 0.45 or more and 0.99 or less; and (2) a crystallization rate of at least one of the monomer A residues and the monomer B residues is less than 14%.