Branched poly (hydroxy acid) and production process thereof
Process for manufacturing a polymer by polycondensation of a hydroxy acid, said polymer comprising at least 80% by weight of units that correspond to the hydroxy acid, according to which at least one polyfunctional reactant capable of giving rise to the formation of a three-dimensional polymer network is mixed with the hydroxy acid, and according to which the mixture is subjected to temperature and pressure conditions and for a duration which are all suitable for giving rise to the formation of the network. Poly(hydroxy acid) (PHA) obtainable by such a process.
1. A process for manufacturing a polymer by polycondensation of a hydroxy acid, said polymer comprising at least 80% by weight of units that correspond to the hydroxy acid, said process comprising the following steps:
mixing with the hydroxy acid at least one polyfunctional reactant capable of giving rise to the formation of a three-dimensional polymer network; and
subjecting the mixture to temperature and pressure conditions and for a duration which are all suitable for giving rise to the formation of the network;
wherein the polyfunctional reactant is an epoxysilane and the hydroxy acid is selected from the group consisting of glycolic acid, lactic acid, and mixtures thereof.
2. The process according to claim 1 , wherein the polyfunctional reactant is glycidyloxypropyltrimethoxysilane.
3. The process according to claim 1 , wherein the polymer is a semicrystalline polymer, and wherein the polycondensation comprises phase A and phase B, wherein the polycondensation is initiated during several hours at a temperature below the melting/crystallization temperature of the polymer in phase A, and is then continued at a temperature close to the melting/crystallization temperature of the polymer until crystallization of said polymer in order to obtain a solid in phase B.
4. The process according to claim 3 , wherein said phase A takes place at atmospheric pressure, and wherein said phase B is initiated at atmospheric pressure then continues under a progressive vacuum until a pressure of less than 10 mbar is attained.
5. The process according to claim 4 , further comprising a solid post-condensation step, wherein the solid is kept under vacuum and is left to rest for several hours at a temperature above its glass transition temperature but below its melting/crystallization temperature.
6. The process according to claim 3 , wherein the solid obtained is subjected to a post-condensation in a microwave device for a duration and under conditions such that they cause the melting thereof.
7. The process according to claim 1 , wherein said polymer is a poly(hydroxy acid) comprising poly(hydroxy acid) chains bridged into a three-dimensional network by polyfunctional molecules.
8. The process according to claim 7 , wherein said poly(hydroxy acid) comprises at least 80% by weight of units that correspond to glycolic or lactic acid in the form of linear oligomer chains, wherein said oligomer chains are joined to one another in a three-dimensional network by one or more multifunctional organic compounds.
9. The process according to claim 7 , wherein said poly(hydroxy acid) is insoluble in hexafluoroisopropanol.
10. The process according to claim 7 , wherein said poly(hydroxy acid) has a non-Newtonian viscoelastic behavior in the melt state, and has a melt viscosity at 240° C. of the order of tens or hundreds of Pa·s at 100 rad/s and of the order of tens of thousands or hundreds of thousands of Pa·s at 1 rad/s.