Method for manufacturing poly(2-hydroxyalkanoic acid), and the poly(2-hydroxyalkanoic acid) obtainable thereby
View Patent ↗A method for manufacturing poly(2-hydroxyalkanoic acid), preferably a poly(lactic acid), is disclosed. The method comprises the steps of: mixing a cyclic diester of a 2-hydroxyalkanoic acid and a polymerization catalyst, polymerizing the cyclic diester to form poly(2-hydroxyalkanoic acid) in liquid phase, adding a peroxide-based compound as a catalyst deactivating agent to the liquid phase, applying a devolatilization step to the liquid phase, and allowing the poly(2-hydroxyalkanoic acid) to solidify, characterized in that an end-capping agent is added to the poly(2-hydroxyalkanoic acid) in the liquid phase. The present invention also relates to a poly(2-hydroxyalkanoic acid), preferably a poly(lactic acid), obtainable with said method characterized in that the polymer has a Mn abs ranging between 10000 and 250000 g/mol, preferably between 20000 and 85000 g/mol.
1. A method for manufacturing poly(2-hydroxyalkanoic acid) having a Mn absolute ranging between 10000 and 250000 g/mol as determined by Gel Permeation Chromatography, the method comprising the steps of:
mixing a cyclic diester of a 2-hydroxyalkanoic acid and a polymerization catalyst,
polymerizing the cyclic diester to form poly(2-hydroxyalkanoic acid) in liquid phase,
adding a peroxide-based compound as a catalyst deactivating agent to the liquid phase,
applying a devolatilisation step to the liquid phase,
adding an end-capping agent to the poly(2-hydroxyalkanoic acid) in the liquid phase, wherein the end-capping agent is an anhydride, and
allowing the poly(2-hydroxyalkanoic acid) to solidify,
thereby preparing a poly(2-hydroxyalkanoicacid) having a MN absolute ranging between 10000 and 250000 g/mol as determined by Gel Permeation Chromatography.
2. The method according to claim 1 , wherein the poly(2-hydroxyalkanoic acid) is a poly(lactic acid).
3. The method according to claim 1 , wherein the end-capping agent is an anhydride in the absence of a solvent.
4. The method according to claim 1 , wherein the anhydride is one selected from the group consisting of phthalic anhydride, acetic anhydride, succinic anhydride and their mixtures.
5. The method according to claim 1 , wherein the peroxide-based compound is an organic peroxide, organic hydroperoxides, or perester.
6. The method according to claim 5 wherein the peroxide-based compound is selected from 1,1,3,3-tetramethylbutylhydroperoxide, benzoyl peroxide, dilauroyl peroxide, tert-butylperoxy-diethylacetate, tert-butylperoxy-2-ethyl hexanoate, tert-butylperoxy-isobutyrate, tert-butylperoxy-acetate, tert-butylperoxy-benzoate, dibenzoyl peroxide, and their mixtures.
7. The method according to claim 1 , wherein the cyclic diester is lactide, the polymerization catalyst is a tin-based catalyst.
8. The method according to claim 7 , wherein the polymerization catalyst is tin(II) 2-ethylhexanoate.
9. The method according to claim 1 , wherein an amount of the added end-capping agent to the poly(2-hydroxyalkanoic acid) in the liquid phase is in the range between 0.1 and 4 molar excess as compared to the amount of end groups of the poly(2-hydroxyalkanoic acid) in the liquid phase.
10. The method according to claim 1 , wherein the end-capping agent and the catalyst deactivating agent are added to the poly(2-hydroxyalkanoic acid) in the liquid phase at different stages of the polymerization process.
11. The method according to claim 1 , wherein the end-capping agent is added prior to the deactivating agent.
12. The method according to claim 11 , wherein the end-capping agent is added prior to the devolatilization step.
13. The method according to claim 11 , wherein the deactivating agent is added after the devolatilization step.
14. The method according to claim 1 , wherein an additional devolatilization step is applied on the formed poly(2-hydroxyalkanoic acid) in the liquid phase after the addition of the deactivating agent.
15. A poly(2-hydroxyalkanoic acid) having a Mn absolute as determined by Gel Permeation Chromatography ranging between 10000 and 250000 g/mol, and wherein the polymer comprises a detectable residue of both an end-capping agent and a peroxide-based compound as a catalyst deactivating agent, wherein the end-capping agent is an anhydride.
16. The poly(2-hydroxyalkanoic acid) according to claim 15 , in which the poly(2-hydroxyalkanoic acid) is a poly(lactic acid).
17. The poly(2-hydroxyalkanoic acid) according to claim 15 , wherein a concentration of cyclic diester in the corresponding polymer is less than 0.5% by weight.
18. The poly(2-hydroxyalkanoic acid) according to claim 15 , wherein a portion of the end groups are derived from an anhydride.
19. The poly(2-hydroxyalkanoic acid) according to claim 15 , wherein a portion of the end groups are carboxylic acid end groups.
20. The poly(2-hydroxyalkanoic acid) according to claim 19 , wherein the carboxylic acid end groups comprise —O—(C═O)R(C═O)—OH, wherein R is a C1 to C8 alkyl.
21. The poly(2-hydroxyalkanoic acid) according to claim 15 , containing a residue of a tin-based catalyst and a residue of 1,1,3,3-tetramethylbutylhydroperoxide.