A method of synthesis of PBAT using group 4 and group 13 initiators

Abstract

The present invention provides a method of synthesis of biodegradable polymer poly(butylene adipate-co-terephthalate) (PBAT) via a polycondensation pathway using monomers adipic acid, terephthalic acid, and 1,4-butanediol. The polycondensation catalysts that are used for the synthesis of PBAT are based on Group 4 metals (Titanium) and Group 13 (Aluminum) metals which are earth abundant. The synthesized PBAT has a high molecular weight, in the range of 300000 KDa.

Description

[0001] DESCRIPTION

[0002] TITLE OF THE INVENTION: A METHOD OF SYNTHESIS OF PBAT USING GROUP 4 AND

[0003] GROUP 13 INITIATORS

[0004] FIELD OF INVENTION

[0005] The present invention is related to synthesis of biodegradable polymer poly(butylene adipate-co- terephthalate) (PBAT) via a polycondensation pathway using monomers adipic acid, terephthalic acid, and 1,4-butanediol. The polycondensation catalysts that are used for the synthesis are based on metals, which are earth abundant (Group 13 -Aluminum and Group 4 - Titanium).

[0006] BACKGROUND OF THE INVENTION

[0007] In the 21st century, plastics have become an integral part of our life. Conventional plastics such as polyethylene (PE), polyvinyl chloride (PVC), etc., have been used extensively in various applications due to their excellent mechanical properties and low cost. The major drawback of using conventional plastics is that they are derived from petroleum feedstock and take a long time to degrade, thus adding to further environmental pollution if not disposed of properly. To combat the problem of increased pollution due to plastics and to achieve sustainable development goals, recycling of used plastics and synthesis of biodegradable polymers could play a crucial role. Biodegradable plastics may be derived from renewable sources or petroleum feedstocks. Synthetic aliphatic polyesters such as polylactide (PLA) and polycaprolactone (PCL) have been extensively studied, but the high cost and poor mechanical properties of the polymer limit their widespread application. On the other hand, aromatic polyesters such as PET can be prepared at a low cost and exhibit excellent mechanical properties but are not biodegradable. Thus, the efficient strategy adopted by some researchers for synthesizing biodegradable polymers with considerably good mechanical properties and biodegradability includes synthesizing copolymers comprising both aromatic and aliphatic units. PBAT is one such copolyester having both aromatic and aliphatic units in the polymer chain backbone prepared by the polycondensation reaction between adipic acid (AA), 1,4 Butanediol (BDO) and terephthalic acid (PTA).

[0008] PBAT is a copolymer formed by the esterification of two monomers: butylene adipate and butylene terephthalate. This synthesis process allows for the combination of the properties of both monomers, resulting in a copolymer with desirable mechanical, thermal, and biodegradation properties. The synthesis of PBAT involves several steps, including the esterification of adipic acid and terephthalic acid with 1,4-butanediol, followed by a polycondensation reaction to obtain the desired copolymer. The synthesis conditions, such as reaction temperature, catalyst type, and monomer ratios, play a crucial role in determining the properties of the resulting PBAT.

[0009] Obtaining high molecular weight PBAT is essential for several reasons. Firstly, high molecular weight polymers generally exhibit better mechanical properties, such as tensile strength and durability. Additionally, they have improved thermal stability and are less prone to degradation during processing. Moreover, higher molecular weights contribute to enhanced melt viscosity, leading to improved processability and enabling PBAT to be used in various conventional plastic processing techniques. Several studies have investigated the synthesis of high molecular weight PBAT, with a focus on optimizing reaction conditions, monomer ratios, catalyst types, and polymerization techniques. The prior art provides insights into the strategies employed to achieve high molecular weight PBAT [1],[2]

[0010] However, PBAT molecule with a molecular weight of over three lakh Dalton has not been reported.

[0011] The present invention provides a method of synthesis of high molecular weight biodegradable PBAT using group 4 and group 13 initiators. PBAT is a sustainable alternative in industries looking to reduce their environmental footprint.

[0012] SUMMARY

[0013] One aspect of the current invention One aspect of the invention is a method of making high molecular weight poly(butylene adipate-co-terephthalate) PBAT polymer using an initiator selected from Gorup 4 or Group 13 initiator , the method comprising the steps of; a. Addition of Dimethyl terephthalate and 1,4-butanediol along with the initiator in a reactor equipped with a nitrogen inlet at a temperature of 150-200 °C followed by carrying out the reaction for 1.5-4 hours along with methanol removal b. Addition of adipic acid and 1,4-butanediol to the reactor in step a. upon cessation of methanol evolution followed by heating the reactor to 210-230 °C to remove water c. Decreasing the pressure of the reactor after water removal and increasing the temperature up to 300°C to obtain crude solid PBAT; wherein the group 4 initiator is Tetraisopropyl Titanate (TIPT) and Group 13 initiator is

[0014] THF coordinated aluminium propoxide or a bimetallic aluminium(III) compound.

[0015] In one aspect, the initiator in step a. and b. is THF coordinated aluminium propoxide or bimetallic aluminium compound.

[0016] In one aspect, the reaction in step a with the group 13 initiator THF coordinated aluminium propoxide is carried out for 3 hours and the reaction in step b. was carried out for 22 hours.

[0017] In one aspect, the reaction in step a with the group 13 initiator aluminium complex (initiator 2) is carried out for 5 hours and the reaction in step b. was carried out for 28 hours.

[0018] In one aspect, the reaction in step a with the group 4 initiator Tetraisopropyl Titanate (TIPT) is carried out for 2 hours and the reaction in step b. was carried out for 20 hours.

[0019] In one aspect, equimolar ratio of dimethyl terephthalate and 1,4-butanediol is added in step a.

[0020] In one aspect, equimolar ratio of adipic acid and 1,4-butanediol is added in step b. In one aspect, amount of group 4 or group 13 initiator added in step a. is 0.05% (wt / wt).

[0021] In one aspect, the amount of group 4 or group 13 initiator added in step b. is 0.05% (wt / wt).In one aspect, reactor in step b. is heated to a temperature of 220°C. In one aspect, the temperature in step c is increased to 280°C. In one aspect ,the methanol is removed by the help of the nitrogen inlet and wherein the nitrogen is pumped at a rate of 45mL / min in step a.

[0022] In one aspect the crude solid PBAT is fdtered followed by drying under a vacuum for 8-10 hours. In one aspect, the molecular weight of synthesized PBAT is in the range of 24000-12000 Daltons. In one aspect, the synthesized PBAT has a polydispersity index greater than 1.

[0023] BRIEF DESCRIPTION OF FIGURES:

[0024] Fig l.A. shows the structure of Aluminum(III) isopropoxide isopropanol adduct

[0025] Fig l.B. shows the structure of bimetallic complex of aluminium(III)

[0026] Fig l.C. shows the structure of titanium propionate adduct

[0027] Fig 2. shows Crude NMR of PBAT (Table 1, entry 1)

[0028] Fig 3. shows trace of PBAT using Initiator 1 (Table 1, Entry 1). Fig. 4. shows GPC trace of PBAT using Initiator 2 (Table 1, Entry 2).

[0029] Fig. 5. shows GPC trace of PBAT using Initiator 3 (Table 1, Entry 3).

[0030] DETAILED DESCRIPTION OF THE INVENTION

[0031] In the following detailed description, a reference is made to the accompanying drawings that form a part hereof, and in which the specific embodiments that may be practiced is shown by way of illustration. These embodiments are described in sufficient detail to enable those skilled in the art to practice the embodiments and it is to be understood that other changes may be made without departing from the scope of the embodiments. The following detailed description is therefore not to be taken in a limiting sense.

[0032] The current invention encompasses a sustainable method of making high molecular weight PBAT polymer.

[0033] The synthesis process of PBAT is complex, requires high esterification temperatures and vacuum conditions to achieve suitable molecular weights for different industrial applications. It has also been observed that various side reactions occur during synthesis, including depolymerization, hydrolytic degradation, and color changes.

[0034] Different grades of PBAT synthesis are available with chain extenders, branching agents, chemical functionalization, and in-situ incorporation of nanocomposites.

[0035] Definitions:

[0036] As used herewith the term “Group 4 initiators” refers to coordination compounds of the second group of transition metals in the periodic table consisting of elements titanium (Ti), zirconium (Zr), hafnium (Hf), and rutherfordium (Rf). The group is also called the titanium group or titanium family after its lightest member. Examples include Tetraisopropyl Titanate (TIPT).

[0037] As used herewith the term “Group 13 initiators” refers to coordination complexes of metals such as aluminium, gallium, indium, thallium that have catalytic activity. Complexes of aluminium with trivalent aluminium (Al3+) have a unique electron-deficient structure , readily combining with ligands to form various aluminium compounds. These are soluble in water, hydrogen chloride, ethanol, chloroform. These compounds serve as a catalyst and a catalyst support in chemical and petrochemical industries. It readily combines with ligands to form various aluminium compounds. Examples include THF coordinated aluminium propoxide , bimetallic aluminium(III) compounds.

[0038] As used herewith, the term “PBAT” or “polybutylene adipate terephthalate” or poly(butylene adipate-co-terephthalate) is an aliphatic-aromatic, biodegradable random copolymer. It is a copolyester made from adipic acid (CAS No. 124-04-9) , 1,4-butanediol (CAS No. 110-63-4), and terephthalic acid (CAS No. 100-21-0). It is structurally composed of a chemical unit of butylene adipate and butylene terephthalate.

[0039] PBAT

[0040] As used herewith the term Polydispersity Index or “PDI” of a polymer is calculated as the ratio of weight average by number average molecular weight. PDI value helps for improved selection of polymers for an application. For monodisperse polymers have the PDI value as 1.

[0041] Step-growth polymerization reactions typically yield values of Mv!Mnof around 2.0 and chaingrowth polymerization yield - / values in the range of 1.5-20.

[0042] Poly (butylene adipate-co-terephthalate) (PBAT) is a well-known aliphatic-aromatic biodegradable random co-polyester. It is structurally composed of a chemical unit of buty lene adipate and butylene terephthalate. Here are some key points about PBAT

[0043] As used herewith the term “reactor”, “reaction system”, reaction refer to a vessel or a flask where the reaction is carried out and may also be referred to as a reaction system that facilitates the reaction amongst one or more reactors.

[0044] EMBODIMENTS The current invention encompasses a method of method of synthesis of biodegradable polymer poly(butylene adipate-co-terephthalate) (PBAT) using group 4 and group 13 metals as initiator compounds.

[0045] The foregoing description of the specific embodiments willfully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and / or adapt for various applications such as specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modifications. However, all such modifications are deemed to be within the scope of the claims.

[0046] One embodiment of the invention is a method of making high molecular weight poly(butylene adipate-co-terephthalate) PBAT polymer using an initiator selected from Gorup 4 or Group 13 initiator , the method comprising the steps of; a) Addition of Dimethyl terephthalate and 1,4-butanediol along with the initiator in a reactor equipped with a nitrogen inlet at a temperature of 150-200 °C followed by carrying out the reaction for 1.5-4 hours along with methanol removal; b) Addition of adipic acid and 1,4-butanediol to the reactor in step a. upon cessation of methanol evolution followed by heating the reactor to 210-230 °C to remove water; c)Decreasing the pressure of the reactor after water removal and increasing the temperature up to 300°C to obtain crude solid PBAT; wherein the group 4 initiator is Tetraisopropyl Titanate (TIPT) and Group 13 initiator is THF coordinated aluminium propoxide or a bimetallic aluminium(III) compound.

[0047] In one embodiment, the initiator in step a. and b. is THF coordinated aluminium propoxide or bimetallic aluminium (III) complex

[0048] In one embodiment, the reaction in step a) with the group 13 initiator THF coordinated aluminium propoxide is carried out for 3 hours and the reaction in step b. was carried out for 22 hours. In one embodiment, the reaction in step a) with the group 13 initiator bimetallic aluminium (III) complex is carried out for 5 hours and the reaction in step b. was carried out for 28 hours.

[0049] In one embodiment, the reaction in step a with the group 4 initiator Tetraisopropyl Titanate (TIPT) is carried out for 2 hours and the reaction in step b. was carried out for 20 hours.

[0050] In one embodiment, equimolar ratio of dimethyl terephthalate and 1,4-butanediol is added in step a.

[0051] In one embodiment , equimolar ratio of adipic acid and 1,4-butanediol is added in step b.

[0052] In one embodiment , the amount of group 4 or group 13 initiator added in step a) is 0.05% (wt / wt) (0.05% by weight to the total wight of the reaction system)

[0053] In one embodiment , the amount of group 4 or group 13 initiator added in step b) is 0.05% (wt / wt) (0.05% by weight to the total wight of the reaction system)

[0054] In one embodiment, the reactor in step b. is heated to a temperature of 220°C.In one embodiment , the reactor in step b. was heated to 220 °C under the nitrogen flow for 6 h to remove water.

[0055] In one embodiment , the temperature in step c is increased to 280°C.In one embodiment, the pressure of the reaction system was decreased to 0.01 mbar in step c.

[0056] In one embodiment, methanol is removed by the help of the nitrogen inlet and wherein the nitrogen is pumped at a rate of 45mL / min in step a.

[0057] In one embodiment, crude solid PBAT is obtained in step c. after 20-30 hours from the reactor.

[0058] In one embodiment, the crude solid PBAT obtained in step c. is filtered followed by drying under a vacuum for 8-10 hours. In one embodiment, the crude solid PBAT is suspended in chloroform before filtration.

[0059] In one embodiment, the molecular weight of synthesized PBAT is in the range of 24000-12000 Daltons. In one embodiment, the synthesized PBAT has a poly dispersity index greater than 1.

[0060] In one embodiment, the method encompassed in the invention does not require a co-catalyst.

[0061] In one embodiment, the method is a solid state condensation method. In one embodiment, the PBAT made by the method encompassed in the invention has applications including packaging, agricultural films such as mulch film, cutlery, disposable tableware, courier bags, clothing, pharmaceutical materials.

[0062] EXAMPLES

[0063] Example 1: Polymerization procedure for PBAT synthesis

[0064] Dimethyl terephthalate (30 g, 0.15 mol), 1,4-butanediol (13.50 g, 0.15 mol) and initiator (0.05% by weight) were added together into a 500 mL three-necked flask (reactor) equipped with a mechanical stirrer, a nitrogen inlet (45.0 mL / min) and a distillation column. The reaction was carried out at 180 °C for different time interval (depends on the initiator: 3h, 5h and 2h for initiator 1, 2 and 3 respectively) with continuous removal of methanol by the help of nitrogen inlet. When the evolution of methanol ceased, a predetermined amount of adipic acid (22 g, 0.15 mol), 1,4-butanediol (13.50 g, 0.15 mol) and initiator (0.05% by weight) was again added into the same reaction flask in an inert atmosphere. Then, the flask was heated to 220 °C under the nitrogen flow for 6 h to remove water. Thereafter, the pressure of the reaction system was decreased to 0.01 mbar and the temperature was increased from 220 to 280 °C during this period. After a stipulated time (22h, 28h and 20h for initiator 1, 2 and 3 respectively) highly viscous liquid formed was cooled down to room temperature in presence of reduce pressure. The crude solid was suspended in chloroform (CHCh) (20mL) and isolated by filtration. The filtered product was dried in a vacuum for 8-10 h.

[0065] Table 1

[0066] Names:

[0067] A is Aluminum(III) isopropoxide isopropanol adduct

[0068] B is a structure represented by Fig.l (B)

[0069] C is a TIPT (titanium propionate adduct) References

[0070] [1] "Synthesis, characterization, and thermal degradation behavior of high molecular weight poly(butylene adipate-co-terephthalate)" by Journal of Applied Polymer Science, 2014.

[0071] [2] "Synthesis of high molecular weight poly(butylene adipate -co-terephthalate) using reactive extrusion" by Polymer Engineering & Science, 2010.

Claims

We Claim:

1. A method of making high molecular weight poly(butylene adipate-co-terephthalate) PBAT polymer using an initiator selected from Gorup 4 or Group 13 initiator , the method comprising the steps of; a. Addition of Dimethyl terephthalate and 1,4-butanediol along with the initiator in a reactor equipped with a nitrogen inlet at a temperature of 150-200 °C followed by carrying out the reaction for 1.5-4 hours along with methanol removal b. Addition of adipic acid and 1,4-butanediol to the reactor in step a. upon cessation of methanol evolution followed by heating the reactor to 210-230 °C to remove water c. Decreasing the pressure of the reactor after water removal and increasing the temperature up to 300°C to obtain crude solid PBAT; wherein the group 4 initiator is Tetraisopropyl Titanate (TIPT) and Group 13 initiator is THF coordinated aluminium propoxide or a bimetallic aluminium(III) compound.

2. The method of claim 1 wherein the initiator in step a. and b. is THF coordinated aluminium propoxide or bimetallic aluminium compound.

3. The method of claim 1 wherein the reaction in step a with the group 13 initiator THF coordinated aluminium propoxide is carried out for 3 hours and the reaction in step b. was carried out for 22 hours.

4. The method of claim 1 wherein the reaction in step a with the group 13 initiator aluminium complex (initiator 2) is carried out for 5 hours and the reaction in step b. was carried out for 28 hours.

5. The method of claim 1 wherein the reaction in step a with the group 4 initiator Tetraisopropyl Titanate (TIPT) is carried out for 2 hours and the reaction in step b. was carried out for 20 hours.

6. The method of claim 1 wherein equimolar ratio of dimethyl terephthalate and 1,4-butanediol is added in step a.

7. The method of claim 1 wherein equimolar ratio of adipic acid and 1,4-butanediol is added in step b.

8. The method of claim 1 wherein the amount of group 4 or group 13 initiator added in step a. is 0.05% (wt / wt). io9. The method of claim 1 wherein the amount of group 4 or group 13 initiator added in step b. is 0.05% (wt / wt).

10. The method of claim 1 wherein the reactor in step b. is heated to a temperature of 220°C.

11. The method of claim 1 wherein the temperature in step c is increased to 280°C.

12. The method of claim 1 wherein the methanol is removed by the help of the nitrogen inlet and wherein the nitrogen is pumped at a rate of 45mL / min in step a.

13. The method of claim 1 wherein the crude solid PBAT is fdtered followed by drying under a vacuum for 8-10 hours.

14. The method of claim 1 wherein the molecular weight of synthesized PBAT is in the range of 24000-12000 Daltons.

15. The method of claim 1 wherein the synthesized PBAT has a polydispersity index greater than 1.

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