PL227029B1 - Method for producing new copolyesters containing segments of poly(lactic acid) - Google Patents

Description

Description of the invention

The subject of the invention is a method of producing new copolyesters containing in their structure blocks of poly (lactic acid) and segments of other polyesters.

Poly (lactic acid) (PLA) is a thermoplastic polymer used in the manufacture of packaging and other biodegradable products. On an industrial scale, it is obtained by ring-opening polymerization of lactide (LA), i.e. the cyclic ester of lactic acid (LAc). Thanks to this method, it is possible to obtain PLA chains of high molar mass [K.M. Nampoothiri, N.R. Nair, R.P. John: Bioresource Technology 101, 8493 (2010)]. On a small scale, copolymers of LA with glycolide and other cyclic esters are also produced, which are used as bioresorbable carriers for drugs and other bioactive substances [J.J. Grodzinski: Polym. Adv. Technol. 17, 395 (2006)].

PLA with high molar mass, on the order of even several hundred thousand g / mol, can also be obtained by direct condensation of LAc in high-boiling solvents forming an azeotrope with water or by solid-state condensation [T. Maharana, B. Mohanty, Y.S. Negi: Progress in Polymer Science 34, 99 (2009)]. However, these methods are much less economical than the processes of LA production from LAc and cyclic monomer polymerization.

As a result of the bulk condensation of LAc, it is very easy to obtain products with molecular weights of several thousand g / mol, which are intermediates for the preparation of LA [G.-X. Chen, H.-S. Kim, E.-S. Kim, J.-S. Yoon: European Polymer Journal 42, 468 (2006)]. By carrying out this process in the presence of difunctional compounds, telechelical products containing the same functional groups (carboxyl or hydroxyl) at the ends of the chain can be obtained. The molar masses (up to 18,000 g / mol) of these products can be increased by combining them into longer chains in a polyaddition reaction thanks to suitable compounds such as diisocyanates. For this reason, the modification of PLA to a telechelic compound is of great importance, which will guarantee the reaction of both ends of the chain and, as a result, obtaining a product with a high molar mass. This was proved by Hiltunen and colleagues [K. Hiltunen, J. V. Seppal, M. Harkonen: J. Appl. Polym. Sci. 64, 865 (1997)], who used e.g. 1,6-dihexamethylene diisocyanate. Increasing the molar mass improved the mechanical properties of the polymer and broadened the scope of its applications.

There are also known processes which use hydroxyl compounds with a functionality greater than two. By carrying out the polycondensation process of LAc using a polyhydroxy compound as a product, a star-shaped PLA is obtained. It has a higher molar mass than the condensation reaction product without the use of a branched compound. Branched hydroxyl compounds in the direct polycondensation of LAc were obtained by Kim et al. [J.-H. Kim, G.-l. Shin, S. H. Kim, Y. H. Kim: Korea Polymer Journal Bioresource Technology 5, 19 (1997)]. They used dipentaerythritol as the multifunctional branched compound, which has six hydroxyl groups. LAc is also condensed using polycarboxylic compounds. Star polymers with carboxyl end groups are characterized by greater solubility and the ability to decompose while maintaining thermal properties [A. Abiko, S. Yano, M. Iguchi: Polymer 53, 3842 (2012)]. However, both branched oligomers with hydroxyl and carboxyl end groups were not used in the further processes.

LAc polymers with molar masses of several thousand g / mol can find practical application as drug carriers or biodegradable coatings for mineral fertilizers or grains. In this case, particularly good mechanical properties are not required, and controlled biodegradability is of key importance. LA homopolymers, due to the high content of the crystalline phase and the high glass transition temperature of the amorphous phase (62 ° C), undergo the process of biodegradation too slowly, however, to be used as biodegradable coatings. As already mentioned, copolymers with other cyclic monomers are thus obtained in order to increase the rate of biodegradation. However, the price of these monomers is relatively high.

An important feature of (multi) telechelic oligomers is that the end groups can then be used in further reactions. So far, only reactions have been described in which the end groups of the linear telechelic oligomers react with chain linkers, e.g. diisocyanates, diepoxides. These reactions were aimed at obtaining PLA of high molecular weight. The aim of the invention was to obtain LAc copolyesters with cheap and readily available monomers

PL 227 029 B1 are cyclic anhydrides and oxiranes. Such copolyesters are characterized by a lower glass transition temperature than the LA homopolymer.

The method of producing new polyesters containing PLA segments according to the invention is a two-step process. In a first step, a (multi) telechelic oligomer is obtained by condensing LAc with at least a trihydroxy compound or mixtures thereof or at least a tricarboxylic acid or mixtures thereof. The reaction is carried out at a temperature of 120 to 250 ° C, preferably 190 ° C, for 5 to 12 hours, preferably 6-8 hours, initially under an inert gas atmosphere and then under successively reduced pressure in the presence of a catalyst. An aqueous solution of LAc with a concentration of 30 to 92%, preferably 80-85%, a catalyst used in an amount not greater than 1 mole% with respect to moles of LAc, preferably 0.2%, and a branching agent: a compound of at least trihydroxy compound are introduced into the vessel. or mixtures thereof or at least tricarboxylic acid or mixtures thereof used in an amount corresponding to 1 / 60-1 / 10 moles of LAc per mole of functional groups present in the branching agent molecule. During the course of the reaction, the pressure is gradually lowered from atmospheric pressure to a pressure of the order of 0.01 mbar. The obtained oligomer is dissolved in dichloromethane and precipitated in methanol.

In the second step, the catalyst is added to the obtained oligomer in an amount not greater than 1 mole m mole of LAc oligomer, and monofunctional heterocyclic monomers. The second stage is carried out at a temperature of 50 to 150 ° C for 12 to 48 hours, preferably 15 hours, under an inert gas atmosphere. The product obtained is dissolved in dichloromethane and precipitated in methanol.

L-lactic acid, D-lactic acid or a mixture thereof with any isomer ratio are used as lactic acid.

The at least trihydroxy compounds are preferably trimethylolpropane, pentaerythritol, dipentaerythritol, glycerin or mixtures thereof, and at least tricarboxylic compounds are preferably 1,2,3,4-butanetetracarboxylic acid, 1,2,4,5-benzenetetracarboxylic acid or their mixtures.

The catalyst used in the first step is preferably antimony (III) oxide, tin (II) chloride, zinc chloride, p-toluenesulfonic acid, zinc and zirconium acetylacetonates or mixtures thereof.

Preference is given to using cyclic dicarboxylic acid anhydrides and olefin oxides as monofunctional heterocyclic monomers.

The cyclic anhydrides of the dicarboxylic acids are preferably maleic anhydride, succinic anhydride, phthalic anhydride or mixtures thereof.

The olefin oxides used are preferably propylene oxide, ethylene oxide or a mixture thereof.

The catalyst used in the second step is preferably magnesium ethoxide, (S, S) -N, N'-bis (3,5-di-tert-butylsalicylidene) -1,2-cyclohexanediaminochrome (III) chloride, (R, R) chloride ) -N, N'-bis (3,5-di-tert-butylsalicylidene) -1,2-cyclohexanediaminomanganese (III), (S, S) -N, N'-bis (3,5-di-tert-butylsalicylidene) -1,2-cyclohexanediaminocobalt (II).

Nitrogen or argon or a mixture thereof is preferably used as the inert gas.

P r z k ł a d 1

LAc oligomer synthesis

A reaction system consisting of a 100 ml two-necked round bottom reaction flask equipped with a magnetic stirring element and to which a Dean-Stark trap was connected via a shunt was assembled. A receiving flask (bottom) and a reflux condenser (top) are attached to the body of the cap. At the outlet of the cooler, an angular cap with a tube was placed, the outlet of which was connected with a hose to a cold trap cooled with dry ice, equipped with a collecting flask. Next, the system was connected to the pressure regulation and measurement system (vacuum-gas line). The Dean-Stark cap was optionally heated by a heating tape. 13.390 g of 85% strength aqueous L-LAc solution and 0.057 g of tin (II) chloride dihydrate catalyst and 0.188 g of 1,2,3,4-butanetetracarboxylic acid were introduced into the reaction flask under nitrogen atmosphere. The flask was connected to the rest of the system and heated at 190 ° C on a magnetic stirrer. The reaction was run for 8 h. During this time, the pressure was gradually reduced from atmospheric pressure to hundredths of a mbar. The obtained oligomer was dissolved in dichloromethane and precipitated in methanol. In this way, an oligomer with a number-average molecular weight of 8100 g / mol (Mn) and a linear polymer chain molar content of 6% was obtained.

P r z k ł a d 2

LAc oligomer synthesis

The oligomer preparation process was carried out in an analogous reaction system as described in Example 1. 66.495 g of 85% aqueous L-LAc, 0.331 tin acetylacetonate were used.

And 0.914 g of 1,2,3,4-butanetetracarboxylic acid. The process conditions were analogous to those in Example 1. The obtained oligomer was dissolved in dichloromethane and precipitated in methanol. In this way, an oligomer with M n = 6600 g / mol, molar content of linear polymer chains of 18.4%, T _g = 57.6 ° C and T _t = 134.5 ° C was obtained.

P r z k ł a d 3

LAc oligomer synthesis

The oligomer preparation process was carried out in an analogous reaction system as described in Example 1. 21.926 g of 85% aqueous L-LAc solution, 0.109 g of zinc acetylacetonate and 0.329 g of 1,2,4,5-benzenetetracarboxylic acid were used. The process conditions were analogous to those in Example 1. The obtained oligomer was dissolved in dichloromethane and precipitated in methanol. In this way, an oligomer with Mn = 5700 g / mol and a molar chain content of a linear polymer of 31.4% was obtained.

P r z k ł a d 4

LAc oligomer synthesis

The oligomer preparation process was carried out in an analogous reaction system as described in Example 1. 20.187 g of 85% aqueous L-LAc solution, 0.186 g of zirconium acetylacetonate and 0.161 g of pentaerythritol were used. The process conditions were analogous to those in Example 1. The obtained oligomer was dissolved in dichloromethane and precipitated in methanol. In this way, an oligomer with Mn = 6000 g / mol and a molar chain content of a linear polymer of 2.2% was obtained.

P r z k ł a d 5

LAc oligomer synthesis

The oligomer preparation process was carried out in an analogous reaction system as described in Example 1. 56.988 g of 85% aqueous L-LAc solution, 0.284 g of zinc acetylacetonate and 0.460 g of pentaerythritol were used. The process conditions were analogous to those in Example 1. The obtained oligomer was dissolved in dichloromethane and precipitated in methanol. In this way, an oligomer with Mn = 4200 g / mol, molar content of linear polymer chains of 14.6% and Tg = 38.9 ° C and Tt = 120.9 ° C was obtained.

P r z k ł a d 6

Synthesis of copolyester

0.513 g of the oligomer prepared according to the method described in example 5, 0.076 g of the catalyst in the form of (S, S) -N, N'-bis (3,5-di-tert-butylsalicylidene) - was introduced into a thick-walled glass ampoule reactor under nitrogen atmosphere. 1,2-cyclohexanediaminochrome (II), 1.424 g of propylene oxide and 2.396 g of maleic anhydride. The reactor was heated at 80 ° C on a magnetic stirrer for 15 h. The obtained oligomer was dissolved in dichloromethane and precipitated in methanol.

The reaction product is a mixture of linear and branched homo- and copolyesters, predominantly the last _one, as shown by analysis of ¹ H NMR, MALDI ToF and GPC. The weight (molar) composition of the obtained product is as follows: propylene oxide units 31.7% (41.1%), maleic anhydride 44.6% (34.2%) and lactic acid 23.7% (24.7%) . The resulting product has Mn = 17,100 g / mol (method ¹ H NMR) Tg = 12.33 ° C. The polymer is amorphous (cf. data from example 5).

P r z k ł a d 7

Synthesis of copolyester

0.444 g of the oligomer prepared according to the procedure described in Example 2, 0.008 g of magnesium ethoxide catalyst, 0.771 g of propylene oxide and 1.296 g of maleic anhydride were introduced into a glass thick-wall ampoule reactor under nitrogen. The process conditions were analogous to those in Example 8. The obtained oligomer was dissolved in dichloromethane and precipitated in methanol. The reaction product is a mixture of linear and branched homo- and copolyesters _1, with a prevalence of the latter, as shown by analysis of ¹ H NMR, MALDI ToF and GPC. The weight (molar) composition of the obtained product is as follows: propylene oxide units 19.9% (25.2%), maleic anhydride 25.5% (19.1%) and lactic acid units 54.6% (55.7%) . The resulting product has Mn = 12,100 g / mol (method ¹ H NMR), Tg = 30.0 ° C and a melting point = 114.4 ° C (cf. The data from Ex. 2).

P r z k ł a d 8

Synthesis of copolyester

1.287 g of the oligomer prepared according to the procedure described in Example 2, 0.022 g of magnesium ethoxide catalyst, 1.132 g of propylene oxide and 1.900 g of maleic anhydride were introduced into a glass thick-wall ampoule reactor under a nitrogen atmosphere. Conditions

The processes were analogous to example 6. The obtained oligomer was dissolved in dichloromethane and precipitated in methanol. The reaction product is a mixture of linear and branched homo- and copolyesters _1, with a prevalence of the latter, as shown by analysis of ¹ H NMR, MALDI ToF and GPC. The weight (molar) composition of the obtained product is as follows: propylene oxide units 22.1% (28.7%), maleic anhydride 36.3% (27.8%) and lactic acid 41.6% (43.5%) . The resulting product has Mn = 16,000 g / mol (method ¹ H NMR), Tg = 17.0 ° C and a melting point = 113.4 ° C (cf. The data from Ex. 2).

P r z k ł a d 9

Synthesis of copolyester

0.837 g of the oligomer prepared according to the method described in example 2, 0.080 g of the catalyst in the form of (S, S) -N, N'-bis (3,5-di-tert-butylsalicylidene) were introduced into a thick-walled glass ampoule reactor under nitrogen atmosphere. 1,2-cyclohexanediaminochrome (II), 1.473 g of propylene oxide and 2.586 g of maleic anhydride. The process conditions were analogous to those in Example 6. The obtained oligomer was dissolved in dichloromethane and precipitated in methanol. The reaction product is a mixture of linear and branched homo- and copolyesters, predominantly the last _one, as shown by analysis of ¹ H NMR, MALDI ToF and GPC. The weight (molar) composition of the obtained product is as follows: propylene oxide units 30.2% (38.7%), maleic anhydride 39.9% (30.3%) and lactic acid 29.9% (31.0%) . The resulting product has Mn = 21,400 g / mol (method ¹ H NMR), Tg = 20.7 ° C and a melting point = 111.3 ° C (cf. The data from Ex. 2).

P r z k ł a d 10

Synthesis of copolyester

0.679 g of the oligomer prepared according to the method described in Example 2, 0.012 g of magnesium ethoxide catalyst, 0.907 g of ethylene oxide and 0.797 g of maleic anhydride were introduced into a glass thick-wall ampoule reactor under nitrogen atmosphere. The process conditions were analogous to those in Example 6. The obtained oligomer was dissolved in dichloromethane and precipitated in methanol. The reaction product is a mixture of linear and branched homo- and copolyesters _1, with a prevalence of the latter, as shown by analysis of ¹ H NMR, MALDI ToF and GPC. The weight (molar) composition of the obtained product is as follows: ethylene oxide units 22.5% (35.1%), maleic anhydride 36.7% (25.8%) and lactic acid 40.8% (39.1%) . The resulting product has Mn = 15,800 g / mol (method ¹ H NMR) Tg = -7.4 ° C and a melting point = 123.9 ° C (cf. The data from Ex. 2).

P r x l a d 11

Synthesis of copolyester

0.964 g of the oligomer prepared according to the procedure described in Example 2, 0.017 g of magnesium ethoxide catalyst, 1.287 g of ethylene oxide and 2.917 g of maleic anhydride were introduced into a glass thick-wall ampoule reactor under a nitrogen atmosphere. The process conditions were analogous to those in Example 6. The obtained oligomer was dissolved in dichloromethane and precipitated in methanol. The reaction product is a mixture of linear and branched homo- and copolyesters _1, with a prevalence of the latter, as shown by analysis of ¹ H NMR, MALDI ToF and GPC. The weight (molar) composition of the obtained product is as follows: ethylene oxide units 27.9% (43.3%), maleic anhydride 46.6% (32.5%) and lactic acid 25.5% (24.2%) . The resulting product has Mn = 25,100 g / mol (method ¹ H NMR) Tg = -4.7 ° C and a melting point = 117.6 ° C (cf. The data from Ex. 2).

Claims (14)

1. The method of producing new polyesters containing poly (lactic acid) segments, characterized in that a catalyst in an amount of not more than 1 mole% in relation to the moles of lactic acid is added to the aqueous solution of lactic acid with a concentration of 30 to 92% by weight, and branching compound: at least trihydroxy compound or mixtures thereof or at least tricarboxylic compound or mixtures thereof used in an amount corresponding to 1 / 60-1 / 10 moles of lactic acid per 1 mole of functional groups present in the branching agent molecule, the reaction being carried out at a temperature from 120 to 250 ° C for 5 to 12 hours, initially under an inert gas atmosphere and then gradually reducing the pressure in the range from atmospheric pressure to Ci6 After a temperature of 0.01 mbar, the obtained oligomer is dissolved in dichloromethane and precipitated in methanol, and then in the second stage the catalyst is added to the obtained oligomer in an amount not greater than 1 mole m mole of lactic acid oligomer, and monofunctional heterocyclic monomers and the reaction is carried out at a temperature of 50 to 150 ° C for 15 to 48 hours under an inert gas atmosphere, and the polymer obtained is dissolved in dichloromethane and precipitated in methanol. 2. The method according to p. The method of claim 1, wherein the lactic acid is L-lactic acid, D-lactic acid or a mixture thereof with any isomer ratio. 3. The method according to p. The process of claim 1, wherein the reaction in the first step is carried out at a temperature of 190 ° C. 4. The method according to p. The process of claim 1, wherein the reaction in the first step is carried out for 6-8 hours. 5. The method according to p. A process as claimed in claim 1, characterized in that an 80-85 wt% aqueous lactic acid solution is used. 6. The method according to p. The process of claim 1, wherein the reaction in the second step is carried out by 15 hours. 7. The method according to p. The process of claim 1, characterized in that the at least trihydroxy compounds are trimethylolpropane, pentaerythritol, dipentaerythritol, glycerin or mixtures thereof, and at least tricarboxylic compounds are adipic acid, sebacic, malonic, succinic, maleic acid 1,2,3,4 -butane tetracarboxylic, 1,2,4,5-benzenetetracarboxylic or mixtures thereof. 8. The method according to p. The process of claim 1, wherein the catalyst in the first step is antimony (III) oxide, tin (II) chloride, zinc chloride, antimony (III) oxide, p-toluenesulfonic acid, zinc and zirconium acetylacetonates or mixtures thereof. 9. The method according to p. The process of claim 1, wherein the amount of catalyst is used in the first step in an amount of 0.2% by weight. 10. The method according to p. The process of claim 1, wherein the heterocyclic monomers are cyclic dicarboxylic acid anhydrides and olefin oxides. 11. The method according to p. The process of claim 10, characterized in that maleic anhydride, succinic anhydride, phthalic anhydride or mixtures thereof are used as the cyclic dicarboxylic acid anhydrides. 12. The method according to p. The process of claim 10, wherein the olefin oxides are propylene oxide and ethylene oxide or a mixture thereof. 13. The method according to p. A process as claimed in claim 1, characterized in that the catalyst in the second step is magnesium ethoxide, (S, S) -N, N'-bis (3,5-di-tert-butylsalicylidene) -1,2-cyclohexanediaminochrome (III) chloride, (R, R) -N, N'-bis (3,5-di-tert-butylsalicylidene) -1,2-cyclohexanediaminomanganese chloride (III), (S, S) -N, N'-bis (3,5 -di-tert-butylsalicylidene) -1,2-cyclohexanediaminocobalt (II). 14. The method according to p. The process of claim 1, wherein the inert gas is nitrogen or argon or a mixture thereof.