Polyglycolic acid resin and production process thereof

A polymer resin comprising one or more repeating units of —(—OCH2—CO—)— or —(—CO—CH2O—)— and one or more bonding units each selected from the group consisting of:

• (a) bonding unit 1 is,
• (b) bonding unit 2 is
• (c) bonding unit 3 is
• (d) bonding unit 4 is
• and
• (e) bonding unit 5 is
• wherein is a polymer segment consisting of a plurality of the repeating unit of —(—OCH2—CO—)— or —(—CO—CH2O—)—;
• R1, R2, R3, R4, R5 and R6 are each an aliphatic or aromatic group;
• wherein bonding unit (a) has 3-20 arms, and each arm (i.e., each of n1, n2 . . . ni) may have 1-2,000, preferably 10-1,000, repeating units of —(—OCH2—CO—)— or —(—CO—CH2O—)—;
• wherein each bonding unit is linked with a repeating unit or another bonding unit via covalent bond;
• and
• wherein the polymer resin has a mean-square radius of gyration of 10-80 nm as measured in hexafluoroisopropanol at 25° C.;
• the polymer resin is prepared by a process comprising the following:
• (a)mixing glycolide with a catalyst, an initiator and a structure regulator A in a prepolymerization reactor at a temperature above the melting temperature of the glycolide and below the melting temperature of the polymer resin, whereby a melted prepolymerization composition is formed;
• (b)polymerizing the melted prepolymerization composition in the presence of a structure regulator B, whereby a melted polymerization composition is formed;
• and
• (c)devolatilizing and modifying the melted polymerization composition, whereby the melted PGA resin is formed.