Description:TECHNICAL FIELD
[0001] The present disclosure relates to a method for preparing polycarbonates. More particularly, the disclosure relates to a one-pot synthesis method for preparing isosorbide-based polycarbonate.

BACKGROUND
[0002] Background description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.
[0003] Limited availability of fossil resources and increase in global warming has led to a shift in research efforts towards high-value chemical products through use of renewable resources (biomass, CO2, etc.) and green synthetic processes. In this regard, commercial thermoplastic engineering plastics (TPE) have been widely used for various applications and are mostly dependent on petroleum derived products as precursors. One such TPE is polycarbonate (PC), which has been industrially applied in various fields due to its brilliant optical transparency, remarkable heat resistance and good mechanical strength. However, the industrial mass production of PC uses the traditional phosgene process, which entails serious inherent drawbacks such as equipment corrosion, environmental pollution, and safety hazards.
[0004] A process that does not require use of phosgene is based on the transesterification of petroleum-based bisphenol A (BPA) with dialkyl carbonate or diaryl carbonate. However, use of a dialkyl carbonate has a disadvantage that in the transesterification with bisphenolacetone, it is not reactive enough under commercially reasonable conditions to form sufficient quantities of polycarbonate. Furthermore, the alkyl alcohol that is liberated is not used in any other part of the process for producing polycarbonate, and recycling of the alkyl alcohol to the dialkyl carbonate production requires substantial purification. Moreover, BPA is an endocrine disrupter and can leach out from food containers made from PC.
[0005] The use of a diaryl carbonate, in particular diphenyl carbonate (DPC), has the advantage that it is reactive enough to form polymeric polycarbonate. Furthermore, phenol is liberated in the reaction of the diphenyl carbonate with bisphenolacetone to form polycarbonate, for instance, as described in US5589564A. The liberated phenol may in turn be recycled to the production of bisphenolacetone or diphenyl carbonate, for which it is a main raw material. However, Diphenyl carbonate is expensive and it is desirable to find a way to carry out this process without the substantial cost of using large amounts of diphenyl carbonate. Furthermore, diaryl carbonate being a non-biobased precursor for synthesizing PC, it is likely to create environmental menace.
[0006] Amongst bio-based precursors, isosorbide has been of major interest. Isosorbide (ISB) is a renewable chiral diol with a V-shaped skeleton structure consisting of two fused furan rings, which endows ISB with a prominent rigidity and optical properties. Additionally, ISB is derived from inexpensive and abundant natural products (cereal starch) and has been already commercially available, which greatly facilitates ISB as a bio-based platform molecule to replace petro-sourced compounds for synthesizing various polymers. Hence, ISB has been regarded as an excellent alternative to BPA for production of PC in terms of molecular properties, industrial reality and environmental friendliness. Compared to the traditional BPA-based PC, poly(isosorbide carbonate) (PIC) has a broader application prospects because PIC possesses enhanced scratch resistance, superior UV stability, and nontoxic nature.
[0007] Till date, to the best of the knowledge of inventors of the present application, the isosorbide-based polycarbonates have been synthesized via melt condensation polymerization method, wherein aliphatic/aromatic carbonate molecule are used as carbonate source, and suitable transesterification catalyst is used to enhance the reaction rate to reduce the possibility of discoloration during the course of reaction. For instance, US10640609B2 discloses a method of producing an oligomer from a dialkyl carbonate and a dihydroxy compound. The process comprises the steps of: a) contacting a dialkyl carbonate with a dihydroxy compound in an oligomerization zone in the presence of an oligomerization catalyst under oligomerization conditions to form a first intermediate; and b) contacting the first intermediate with a diaryl carbonate in a polymerization zone in the presence of a polymerization catalyst under polymerization conditions to produce the polycarbonate, the molar ratio of dihydroxy compound to dialkyl carbonate in the oligomerization zone being maintained at least 2:1. US7666972B2 discloses isosorbide-based polycarbonates prepared by melt polymerization method using an activated carbonate source in the presence of a catalyst, the resultant isosorbide-based polycarbonates having low background color, good UV stability, and good Mw stability.
[0008] Although, few methods for synthesizing PC are known in the art, a need has been felt in the state-of-art of a process that is - less complex, economical and easy to scale-up that result in polycarbonate (hereinafter also referred to as “PC”) with beneficial properties such as, but not limited to, high yield, high thermal stability, high transparency, high scratch resistivity, lower oxygen permeability, color stability and good transparency. A need is also felt of novel catalyst system that imparts PC and the method of preparation thereof with the aforementioned benefits.
[0009] All publications herein are incorporated by reference to the same extent as if each individual publication or patent application were specifically and individually indicated to be incorporated by reference. Where a definition or use of a term in an incorporated reference is inconsistent or contrary to the definition of that term provided herein, the definition of that term provided herein applies and the definition of that term in the reference does not apply.

OBJECTS
[0010] An object of the present disclosure is to arrive at a one-pot synthesis method for preparing polycarbonate, which is economical, bio-based, capable of being easily scaled-up to industrial capacities resulting in high yields of polycarbonate.
[0011] Another object of the present disclosure is to provide a polycarbonate having desired properties such as, but not limited to, high thermal stability, high transparency, high scratch resistivity, lower oxygen permeability, color stability and good transparency.

SUMMARY
[0012] The present disclosure relates to a method for preparing polycarbonates. More particularly, the disclosure relates to a one-pot synthesis method for preparing isosorbide-based polycarbonate.
[0013] Surprisingly, it has been found that the above object is met by providing a one-pot synthesis method for preparing isosorbide-based polycarbonate in presence of a transesterification catalyst, which is a supported or unsupported tin catalyst selected from the group consisting of: stannous chloride, dibutyl tin dichloride,dibutyl tin diacetate, dibutyl tin oxide, dibutyl tin dilaurate, tin-2-ethylhexanoate, butyl stannoic acid, and butyltin hydroxide-oxide.
[0014] Accordingly, in one aspect, the present disclosure relates to a one-pot synthesis method for preparing a polycarbonate, the method including reacting a dihydroxy compound with a carbonate compound in presence of a transesterification catalyst. The transesterification catalyst is a tin catalyst selected from the group consisting of: stannous chloride, dibutyl tin dichloride, dibutyl tin diacetate, dibutyl tin oxide, dibutyl tin dilaurate, tin-2-ethylhexanoate, butyl stannoic acid, and butyltin hydroxide-oxide. The weight ratio between the dihydroxy compound and the carbonate compound is in the range of 3.0:2.0 to 1.0:10.0.
[0015] In some embodiments, the tin catalyst comprises a supported tin catalyst, an unsupported tin catalyst or combinations thereof.
[0016] In some embodiments, the tin catalyst is dibutyl tin dilaurate, butyltin hydroxide-oxide or combinations thereof.
[0017] In some embodiments, the tin catalyst is a supported tin catalyst including an inorganic support selected from the group consisting of: alumina, magnesium chloride, magnesium oxide, titania, and silica.
[0018] In some embodiments, the dihydroxy compound includes a dianhydrohexitol selected from any or a combination of: isosorbide, isomannide, isoidide, and isomers thereof.
[0019] In some embodiments, the dihydroxy compound further includes a second dihydroxy compound selected from: an acid, a diol and mixtures thereof. In some embodiments, the acid is selected from dodecanedioic acid, adipic acid, hexanedioic acid, isophthalic acid, benzenedicarboxylic acid, teraphthalic acid, naphthalene dicarboxylic acid, hydroxybenzoic acid, and mixtures thereof. In some embodiments, the diol is selected from 1,4-butane diol, tricyclodecane dimethanol, bis(hydroxymethyl)tricyclodecane, tetramethyl cyclobutanediol, cyclohexanedimethanol, bis(hydroxymethyl)cyclohexane, cyclohexylenedimethanol, bi(cyclohexyl) diol, dicylcohexyl-4,4'-diol, dihydroxybicyclohexyl, ethylene glycol, propylene glycol, hexanediol, resorcinol, catechol, hydroquinol,isomers, polymers, and mixtures thereof.
[0020] In some embodiments, the amount of the second dihydroxy compound ranges from 5 wt.% to 50 wt.% based on the total weight of the dihydroxy compound.
[0021] In some embodiments, the carbonate compound is selected from: (a) a dialkyl carbonate represented by the formula R1OCOOR1 or R1OCOOR2, wherein R1 and R2 represents: a linear or branched, substituted or unsubstituted alkyl group having 1 to 10 carbon atoms, or an alicyclic group having 3 to 10 carbon atoms, or a substituted or unsubstituted aralkyl group having 6 to 10 carbon atoms; and (b) a diaryl carbonate represented by the formula R3OCOOR3 or R3OCOOR4, wherein R3 and R4 represents: an aryl group having 6 to 20 carbon atoms, or a heteroaryl group having 6 to 20 carbon atoms.
[0022] In some embodiments, the step of reacting includes: (a) mixing the dihydroxy compound, the carbonate compound, and the transesterification catalyst to obtain a reaction mixture; (b) subjecting the reaction mixture to transesterification at a temperature ranging between 90°C to 140°C for a duration ranging between 2 hours to 8 hours; and (c) subjecting the trans-esterified reaction mixture to polycondensation at a temperature ranging between 140°C to 300°C for a duration ranging from 1 hour to 4 hours to obtain the polycarbonate. In some embodiments, the reaction mixture is subjected to transesterification at a temperature ranging between 90°C to 140°C at atmospheric pressure for a duration ranging between 2 hours to 8 hours. In some embodiments, the trans-esterified reaction mixture is subjected to polycondensation at a temperature ranging between 140°C to 300°C and at pressure less than 0.5 bar for a duration ranging from 1 hour to 4 hours to obtain the polycarbonate.
[0023] In some embodiments, the polycarbonate has a number average molecular weight ranging from 5.0 x 103 g/mol to 5.0 x 104 g/mol. In some embodiments, the polycarbonate has a glass transition temperature ranging between 110°C to 150°C when determined in accordance with ASTM D 3418.
[0024] Another aspect of the present disclosure provides a polycarbonate obtained from the method of the present disclosure.
[0025] Further aspect of the present disclosure provides a shaped article made from the polycarbonate obtained from the method of the present disclosure.
[0026] Various objects, features, aspects and advantages of the inventive subject matter will become more apparent from the following detailed description of preferred embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS
[0027] The accompanying drawings are included to provide a further understanding of the present disclosure, and are incorporated in and constitute a part of this specification. The drawings illustrate exemplary embodiments of the present disclosure and, together with the description, serve to explain the principles of the present disclosure.
[0028] FIG. 1 illustrates an exemplary 1H NMR spectrum of a polycarbonate realized in accordance with embodiments of the present disclosure.
[0029] FIG. 2 illustrates an exemplary solid-state 13C NMR spectrum of a polycarbonate realized in accordance with embodiments of the present disclosure.
[0030] FIG. 3 illustrates an exemplary Fourier Transform Infrared (FTIR) spectrum of a polycarbonate realized in accordance with embodiments of the present disclosure.

DETAILED DESCRIPTION
[0031] The following is a detailed description of embodiments of the present invention. The embodiments are in such detail as to clearly communicate the invention. However, the amount of detail offered is not intended to limit the anticipated variations of embodiments; on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present invention as defined by the appended claims.
[0032] Each of the appended claims defines a separate invention, which for infringement purposes is recognized as including equivalents to the various elements or limitations specified in the claims. Depending on the context, all references below to the “invention” may in some cases refer to certain specific embodiments only. In other cases it will be recognized that references to the “invention” will refer to subject matter recited in one or more, but not necessarily all, of the claims.
[0033] Groupings of alternative elements or embodiments of the invention disclosed herein are not to be construed as limitations. Each group member can be referred to and claimed individually or in any combination with other members of the group or other elements found herein. One or more members of a group can be included in, or deleted from, a group for reasons of convenience and/or patentability.
[0034] Unless the context requires otherwise, throughout the specification which follow, the word “comprise” and variations thereof, such as, “comprises” and “comprising” are to be construed in an open, inclusive sense that is as “including, but not limited to.” It is to be appreciated that the terms "comprising", "comprises" and "comprised of" as used herein includes the terms "consisting of", "consists" and "consists of" within their meaning.
[0035] Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, the appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.
[0036] As used in the description herein and throughout the claims that follow, the meaning of “a,” “an,” and “the” includes plural reference unless the context clearly dictates otherwise. Also, as used in the description herein, the meaning of “in” includes “in” and “on” unless the context clearly dictates otherwise.
[0037] In some embodiments, the numbers expressing quantities of ingredients, properties such as concentration, and so forth, used to describe and claim certain embodiments of the invention are to be understood as being modified in some instances by the term “about.” Accordingly, in some embodiments, the numerical parameters set forth in the written description are approximations that can vary depending upon the desired properties sought to be obtained by a particular embodiment. In some embodiments, the numerical parameters should be construed in light of the number of reported significant digits and by applying ordinary rounding techniques. Notwithstanding that the numerical ranges and parameters setting forth the broad scope of some embodiments of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as practicable.
[0038] The recitation of ranges of values herein is merely intended to serve as a shorthand method of referring individually to each separate value falling within the range. Unless otherwise indicated herein, each individual value is incorporated into the specification as if it were individually recited herein.
[0039] The headings and abstract of the invention provided herein are for convenience only and do not interpret the scope or meaning of the embodiments.
[0040] All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g. “such as”) provided with respect to certain embodiments herein is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention otherwise claimed. No language in the specification should be construed as indicating any non-claimed element essential to the practice of the invention.
[0041] The following discussion provides many example embodiments of the inventive subject matter. Although each embodiment represents a single combination of inventive elements, the inventive subject matter is considered to include all possible combinations of the disclosed elements. Thus if one embodiment comprises elements A, B, and C, and a second embodiment comprises elements B and D, then the inventive subject matter is also considered to include other remaining combinations of A, B, C, or D, even if not explicitly disclosed.
[0042] Various terms as used herein are shown below. To the extent a term used in a claim is not defined below, it should be given the broadest definition persons in the pertinent art have given that term as reflected in printed publications and issued patents at the time of filing.
[0043] The present disclosure relates to a method for preparing polycarbonates. More particularly, the disclosure relates to a one-pot synthesis method for preparing isosorbide-based polycarbonate.
[0044] An aspect of the present disclosure relates to a one-pot synthesis method for preparing a polycarbonate, the method including reacting a dihydroxy compound with a carbonate compound in presence of a transesterification catalyst.
[0045] For the purpose of the present disclosure, the term "one-pot" refers to a strategy to improve the efficiency of a chemical reaction whereby a reactant is subjected to successive chemical reactions in just one reactor. This is much desired from industry perspective because avoiding a lengthy separation process and purification of the intermediate chemical compounds saves time and resources while increasing chemical yield and reducing the waste.
[0046] As used herein, the term “polycarbonate” includes generally homopolycarbonates and copolycarbonates having repeating structural carbonate units of the Formula I:

Formula I
wherein the R groups are derived from dihydroxy compounds.
[0047] In some embodiments, the transesterification catalyst is a tin catalyst selected from the group consisting of: stannous chloride, dibutyl tin dichloride, dibutyl tin diacetate, dibutyl tin oxide, dibutyl tin dilaurate, tin-2-ethylhexanoate, butyl stannoic acid, and butyltin hydroxide-oxide. In some embodiments, the tin catalyst is dibutyl tin dilaurate, butyltin hydroxide-oxide or combinations thereof.
[0048] In some embodiments, the tin catalyst includes a supported tin catalyst, an unsupported tin catalyst or combinations thereof.
[0049] In some embodiments, the tin catalyst includes an unsupported tin catalyst selected from the group consisting of stannous chloride, dibutyl tin dichloride, dibutyl tin diacetate, dibutyl tin oxide, dibutyl tin dilaurate, tin-2-ethylhexanoate, butyl stannoic acid, and butyltin hydroxide-oxide.
[0050] In some embodiments, the unsupported tin catalyst is selected from the group consisting of dibutyl tin dilaurate, tin-2-ethylhexanoate, butyl stannoic acid, and butyltin hydroxide-oxide.
[0051] In some embodiments, the unsupported tin catalyst is dibutyl tin dilaurate, butyl tin hydroxide-oxide or combinations thereof.
[0052] In some embodiments, the transesterification catalyst is a supported tin catalyst selected from the group consisting of: stannous chloride, dibutyl tin dichloride, dibutyl tin diacetate, dibutyl tin oxide, dibutyl tin dilaurate, tin-2-ethylhexanoate, butyl stannoic acid, and butyltin hydroxide-oxide.
[0053] In some embodiments, the supported tin catalyst is selected from the group consisting of dibutyl tin dilaurate, tin-2-ethylhexanoate, butyl stannoic acid, and butyltin hydroxide-oxide.
[0054] In some embodiments, the supported tin catalyst is dibutyl tin dilaurate, butyl tin hydroxide-oxide or combinations thereof.
[0055] In the present context, a supported catalyst is supported on some sort of a surface, structure or support, and typically comprises an inert support material and a catalytically active material. The catalytically active material is selected from one or more of the above disclosed materials. Suitable support materials are known to the person skilled in the art. In some embodiments, the support material is an inorganic support selected from the group consisting of: alumina, magnesium chloride, magnesium oxide, titania, silica and combinations thereof.
[0056] In some embodiments, the supported tin catalyst has a tin loading in the range of 5wt.% to 30 wt.% based on the total weight of the catalyst. In some embodiments, the tin loading ranges between 5wt.% to 25 wt.%, or 10wt.% to 25 wt.%, or 10wt.% to 20 wt.%.
[0057] In some embodiments, the catalyst concentration ranges between 250 ppm to 8000 ppm with respect to the dihydroxy compound. In some embodiments, the tin loading ranges between 250 ppm to 7000 ppm, or 250 ppm to 6000 ppm, or 250 ppm to 5000 ppm, or 300 ppm to 4000 ppm, or 300 ppm to 3000 ppm, or 300 ppm to 2000 ppm.
[0058] The catalysts of the present disclosure have been found to be stable. As a consequence, there is no or minimal impact of reaction temperature on the polycarbonate quality. Moreover, recyclability of the catalyst is minimum 3-5 cycles without substantially affecting the polycarbonate properties. Another advantage of the catalyst, particularly the supported catalyst, is that it can be removed from the reaction mixtures efficiently. Consequently, the residual metal is not found in the final polycarbonate.
[0059] In some embodiments, the dihydroxy compound includes a dianhydrohexitol. Dianhydrohexitols are by-products of the starch industry obtained by dehydration of D-hexitols, which are made by a simple reduction of hexose sugars. These chiral biomass-derived products exist as three main isomers viz. isosorbide, isomannide, and isoidide, derived from D-glucose, D-mannose, and L-fructose, respectively, depending on the configuration of the two hydroxyl groups.
[0060] In some embodiments, the dianhydrohextol is selected from isosorbide, isomannide, isoidide, isomers thereof, and mixtures thereof. In one embodiment, the dianhydrohexitol is isosorbide. Isosorbide is a low melting (melting point of about 60°C), water soluble, bio-sourced compound derived from sorbitol by a double dehydration, thereby giving the biobased nature to the present invention.
[0061] In some embodiments, the dihydroxy compound further includes a second dihydroxy compound. The second dihydroxy compound can be selected from: an acid, a diol and mixtures thereof. Suitable acids for this purpose includes, but not limited to, dodecanedioic acid, adipic acid, hexanedioic acid, isophthalic acid, benzenedicarboxylic acid, teraphthalic acid, naphthalene dicarboxylic acid, hydroxybenzoic acid, and mixtures thereof. Suitable diols for this purpose includes, but not limited to, 1,4-butane diol, tricyclodecane dimethanol, bis(hydroxymethyl)tricyclodecane, tetramethyl cyclobutanediol, cyclohexanedimethanol, bis(hydroxymethyl)cyclohexane, cyclohexylenedimethanol, bi(cyclohexyl) diol, dicylcohexyl-4,4'-diol, dihydroxybicyclohexyl, ethylene glycol, propylene glycol, hexanediol, resorcinol, catechol, hydroquinol,isomers, polymers, and mixtures thereof.
[0062] In some embodiments, the amount of the second dihydroxy compound ranges from about 5 wt.% to about 50 wt.% based on the total weight of the dihydroxy compound. In some embodiments, the amount ranges from 10 wt.% to 50 wt.%, or 15 wt.% to 50 wt.%, or 20 wt.% to 45 wt.%, or 25 wt.% to 45 wt.%, or 30 wt.% to 45 wt.%.
[0063] Suitable carbonate compounds include alkyl carbonates and aryl carbonates. In some embodiments, the carbonate compound is a dialkyl carbonate. In some embodiments, the dialkyl carbonate is represented by the formula R1OCOOR1 or R1OCOOR2, wherein, R1 and R2 represent a linear or branched, substituted or unsubstituted alkyl group having 1 to 10 carbon atoms, or an alicyclic group having 3 to 10 carbon atoms, or a substituted or unsubstituted aralkyl group having 6 to 10 carbon atoms. Examples of R1and R2 include an alkyl group, such as methyl, ethyl, propyl, allyl, butyl, butenyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl and cyclohexylmethyl and isomers thereof. Further examples of R1and R2 include an alicyclic group, such as cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, and cycloheptyl. Still further examples of R1and R2 include an aralkyl group, such as benzyl, phenethyl, phenylpropyl, phenylbutyl, methylbenzyl and isomers thereof.
[0064] In some embodiments, the alkyl, alicyclic or aralkyl group may be substituted with a substituent such as a lower alkyl group, a lower alkoxy group, a cyano group and a halogen atom. Examples of the dialkyl carbonate where the alkyl groups are the same are dimethyl carbonate, diethyl carbonate, dipropyl carbonate, diallyl carbonate, dibutenyl carbonate, dibutyl carbonate, dipentyl carbonate, dihexyl carbonate, diheptyl carbonate, dioctyl carbonate, dinonyl carbonate, didecyl carbonate, dicyclopentyl carbonate, dicyclohexyl carbonate, dicycloheptyl carbonate, bis(methyl salicyl) carbonate, and isomers thereof.
[0065] Examples of the dialkyl carbonate where the alkyl groups are different are methylethyl carbonate, methylpropyl carbonate, methylbutyl carbonate, methylbutenyl carbonate, methylpentyl carbonate, methylhexyl carbonate, methylheptyl carbonate, methyloctyl carbonate, methylnonyl carbonate, and methyldecyl carbonate, bis(methyl salicyl) carbonate, and isomers thereof. Further examples include: any combination of alkyl groups having 1 to 10 carbon atoms, for example, ethylpropyl carbonate, ethylbutyl carbonate, propylbutyl carbonate and isomers thereof.
[0066] In some embodiments, the carbonate compound is selected from dimethyl carbonate, diethyl carbonate, dipropyl carbonate, diallyl carbonate, dibutenyl carbonate,dibutyl carbonate, dipentyl carbonate, dihexyl carbonate, diheptyl carbonate, dioctyl carbonate, dinonyl carbonate, didecyl carbonate, dicyclopentyl carbonate, dicycloheptyl carbonate, bis(methyl salicyl) carbonate, isomers, and mixtures thereof. In an embodiment, the carbonate compound is dimethyl carbonate.
[0067] In some embodiments, the carbonate compound is a diaryl carbonate represented by the formula R3OCOOR3 or R3OCOOR4, wherein, R3 and R4 represent an aryl group having 6 to 20 carbon atoms, or a heteroaryl group having 6 to 20 carbon atoms. In an embodiment, the carbonate compound is diphenyl carbonate.
[0068] As used herein, the term "aryl" refers to a monocyclic or fused bicyclic, tricyclic or greater, aromatic ring assembly, for example, phenyl, benzyl or naphthyl. Further, "heteroaryl" means a monocyclic or polycyclic ring assembly, wherein at least one ring atom is a heteroatom and the remaining ring atoms are carbon, and at least one of the rings comprises the ring assembly is an aromatic ring.
[0069] In some embodiments, the weight ratio between the dihydroxy compound and the carbonate compound is in the range of 3.0:2.0 to 1.0:10.0. In some embodiments, the weight ratio ranges between 3.0:2.0 to 1.0:8.0, or 3.0:2.0 to 1.0:6.0, or 3.0:2.0 to 1.0:5.0, or 3.0:2.0 to 1.0:4.0.
[0070] In some embodiments, the step of reacting the dihydroxy compound with the carbonate compound in presence of the transesterification catalyst includes: (a) mixing the dihydroxy compound, the carbonate compound, and the transesterification catalyst to obtain a reaction mixture; (b) subjecting the reaction mixture to transesterification at a temperature ranging between 90°C to 140°C for a duration ranging between 2 hours to 8 hours; and (c) subjecting the trans-esterified reaction mixture to polycondensation at a temperature ranging between 140°C to 300°C for a duration ranging from 1 hour to 4 hours to obtain the polycarbonate.
[0071] As noted hereinabove, the present disclosure describes a one-pot, two-step synthesis route for polycarbonate. Primarily, these steps include transesterification and polycondensation, represented by steps (b) and (c), respectively, above.
[0072] In some embodiments, the reaction mixture is subjected to transesterification at a temperature ranging between 90°C to 140°C at atmospheric pressure for a duration ranging between 2 hours to 8 hours.
[0073] In some embodiments, the trans-esterified reaction mixture is subjected to polycondensation at a temperature ranging between 140°C to 300°C and at pressure less than 0.5 bar (for example, between 0.0001 to 0.49 bar pressure or between 0.01 to 0.49 bar pressure) for a duration ranging from 1 hour to 4 hours to obtain the polycarbonate.
[0074] In some embodiments, the temperature for transesterification step ranges between 95°C to 140°C for a duration ranging from about 3 hours to about 5 hours at atmospheric pressure. The temperature is then gradually increased up to 270°C while reducing the pressure to below 0.5 bar to effect the polycondensation. In an embodiment, the following temperature increment sequence is followed: 160°C for 10 min, 180°C for 30 min, 190°C for 10 min, 200°C for 10 min, 220°C for 10 min, 240°C for 10 min, and 270°C for 20 min.
[0075] Unless specified otherwise, mixing in the present disclosure involves agitation by mechanical means. Such techniques for agitation by mechanical means are known to the person skilled in the art. However, such mechanical means may be, such as but not limited to, a stirrer.
[0076] The polycarbonate obtained in accordance with the present disclosure has a number average molecular weight (Mw) ranging between 5.0 x 103 g/mol to 5.0 x 104 g/mol. In some embodiments, Mw ranges between 7.0 x 103 g/mol to 4.0 x 104 g/mol, or 8.0 x 103 g/mol to 3.0 x 104 g/mol.
[0077] The polycarbonate obtained in accordance with some embodiments of the present disclosure has a glass transition temperature (Tg) ranging between 110°C to 150°C. Differential Scanning Calorimeter is used to determine the glass transition, crystallization and melting temperatures of the polycarbonate, in accordance with ASTM D 3418.
[0078] The polycarbonate obtained in accordance with some embodiments of the present disclosure has desired properties such as but not limited to, high thermal stability, high transparency, high scratch resistivity, lower oxygen permeability and color stable. Exemplary details wherefor are provided in the example section.
[0079] The polycarbonate obtained in accordance with some embodiments of the present disclosure is color stable and has good transparency in accordance with ASTM D 2244.
[0080] As described herein, the polycarbonate of the present disclosure is biobased and shows very good thermal stability as confirmed by thermogravimetric analysis. Further, the polycarbonate shows high transparency, high scratch resistivity, low oxygen permeability compared to conventional bisphenol-based polycarbonate. Owing to these properties, the resultant polycarbonate finds application in making various shaped articles. As the name suggests, the shaped article may have any shape and size.
[0081] Accordingly, another aspect of the present disclosure is directed to a polycarbonate obtained from the method, as described herein above. Accordingly, the embodiments pertaining to the method are applicable here as well.
[0082] Further aspect of the present disclosure relates to a shaped article made from the polycarbonate obtained from the method, as described herein above. Accordingly, the embodiments pertaining to the method are applicable here as well. Suitable examples of the shaped article include, but are not limited to, household appliances, electronic items, automobile application, and the likes.
[0083] While the foregoing description discloses various embodiments of the disclosure, other and further embodiments of the invention may be devised without departing from the basic scope of the disclosure. The invention is not limited to the described embodiments, versions or examples, which are included to enable a person having ordinary skill in the art to make and use the invention when combined with information and knowledge available to the person having ordinary skill in the art.
EXAMPLES
[0084] 1,4:3,6-dianhydro-D-glucitol (also known as D-Isosorbide) as a Dihydroxy compound; and Dimethyl carbonate (DMC), Diethyl carbonate (DEC), Diethyl methyl carbonate (DEMC), and Diphenyl carbonate (DPC) as carbonate compound purchased form Sigma-Aldrich India were used in the experiments. Stannous chloride (TC), Dibutyl tin diacetate (DBTDA), Dibutyl tin oxide (DBTO), Dibutyl tin dilaurate (DBTDL), Tin-2-ethylhexanoate (TEH), Butyltin hydroxide-oxide (BTA), and Dibutyl tin dichloride (DBTC) as Transesterification catalyst purchased from TCI Chemicals India were used in the experiments.
[0085] Testing methods:
[0086] Fourier Transform Infrared Spectroscopy (FTIR): FTIR spectra were recorded with Perkin Elmer Spectrum GX equipment (Waltham, Massachusetts, USA). Samples were scanned with a resolution of 2 cm-1 in the scan range of 4000-400 cm-1.
[0087] NMR analysis: 1H and 13C-NMR spectra were recorded on Bruker Avance 500 MHz spectrometer. Deuterated solvents for NMR experiments were obtained from Aldrich Chemical Co.
[0088] GPC analysis: The number average molecular weight and polydispersity index was determined by GPC analysis using chloroform as an eluent and polystyrene as an internal standard.
[0089] Thermal Properties: Differential Scanning Calorimetry (DSC Discovery 2500, TA Instruments Ltd, USA) characterization was performed to determine the glass transition temperature (Tg), crystallization and melting behavior of the polycarbonate, as per ASTM D 3418. Melting point of the synthesized molecules were determined by using capillary in melting point apparatus.
[0090] Example 1 and 2: Synthesis of homopolycarbonates using unsupported catalyst
[0091] Isosorbide based homopolycarbonates were synthesized via one-pot melt polymerization of the dihydroxy compound and the carbonate compound. In the transesterification stage, the dihydroxy compound, the carbonate compound and DBTDL (1 × 10-3 equiv. mol based on the dihydroxy compound) in suitable amounts (mentioned in Table 1 below) were added into a 1 L round bottom flask, which was equipped with a reflux condenser, a nitrogen inlet, a sampling inlet and a mechanical stirrer. The reactants were stirred at 98°C for 5 h to obtain the reaction mixture. The reaction mixture was then heated to 180°C to 187°C and kept for 0.5 h to remove unreacted carbonate compound. In the polycondensation stage, the reaction temperature was gradually increased from 180°C to 240°C and the pressure was reduced to 100 Pa (0.001 Bar). After stirring the mixture for 1 h, the obtained polycarbonate was dissolved in dichloromethane and precipitated with methanol. Finally, the polycarbonate was vacuum dried at 60°C for 24 h which resulted in an isolated yield of about 92%. Details of the reactants are provided below in Table 1 below.
Table 1: Details of the reactants
Reactants Example 1 Example 2
Isosorbide 100 g 50 g
DMC 300 g --
DPC -- 74 g

[0092] Figures 1 to 3 depict 1H NMR spectrum, 13C NMR spectrum, and FTIR spectrum, respectively, of the resultant homopolycarbonate from Example 2.
[0093] Example 3: Synthesis of Copolycarbonate using unsupported catalyst
[0094] Isosorbide (30 g), 1,4-butane diol (18.5 g), DPC (44.5 g) and DBTDL (1 × 10-3 equiv. mol based on the dihydroxy compound) were added into a 250 mL round-bottom flask, which was equipped with a reflux condenser, a nitrogen (N2) inlet, a sampling inlet, and a mechanical stirrer. The reactants were stirred at 98°C for 5 h to obtain the reaction mixture. The reaction mixture was then heated to 180°C to 187°C and kept for 0.5 h to remove unreacted phenol. In the polycondensation stage, the reaction temperature was gradually increased from 180°C to 230°C and the pressure was reduced to 100 Pa. After stirring the mixture for 1 h, the obtained polycarbonate was dissolved in dichloromethane and precipitated with methanol. Finally, the polycarbonate was vacuum dried at 60°C for 24 h, which resulted in an isolated yield of about 90%.
[0095] Examples 4-6: Copolycarbonate using silica supported catalyst
[0096] Silica supported catalyst preparation: 30g of preconditioned silica gel was taken and refluxed for 2h at temperature ranging between 110°Cto 120°C in 750 mL toluene. Subsequently, tin chloride (6 g, 20 wt.%) dispersed in 40 mL toluene was added to the mixture and allowed to react for 5h under same reflux condition. The mixture was then filtered and washed thrice with absolute ethanol and dried at 373K, which gave about 85% yield.
[0097] Synthesis of Copolycarbonate: Isosorbide (25g), DPC (37g), and activated silica supported tin chloride obtained above (2.5g) were taken together in a 500 ml round bottomed flask (R.B.). The reaction mixture was heated at 98°C under N2 atmosphere with continuous stirring for 6 hours at 1 atm. pressure. Subsequently, the reaction temperature was raised slowly to 180°C and later to 220°C. The pressure of the system was also gradually decreased to < 0.1 mm Hg to remove the by-product, i.e., phenol. This operation was continued for 2h to obtain a viscous polymer. Finally, the viscous polymer was dissolved in dichloromethane and precipitated in cold methanol. The white polymer was collected and dried in a vacuum oven at 60°C for 48h, which resulted in an isolated yield of about 90%.
[0098] Experiments were repeated with magnesium chloride support (Example 5) and alumina support (Example 6) for the catalyst with other conditions remaining the same as in Example 4.
[0099] Effect of catalysts on thermal properties of the homopolycarbonates
[00100] Homopolycarbonates were prepared in accordance with the synthesis method detailed in Examples 1 and 2 above using isosorbide and DPC (weight ratio of 1.0:1.01) as the reactants. However, each time a different catalyst was used to study its effect on thermal properties of the resultant polycarbonates. The results are summarized in Table 2 below:
Table 2: Effect of catalyst on Thermal Properties
Catalyst Mn (g/gmol) Tg (°C) TGA (Td, 5%)
Unsupported catalyst
TC 13500 134 295
DBTC 12400 129.7 293.71
DBTO 14000 135 304.23
TEH 13800 132.59 298.57
DBTDA 13100 132.42 291.19
DBTDL 16500 138.1 313.51
BTA 13700 133 301.4
Supported catalyst
Silica supported DBTDL
(20% tin loading) 13900 113.4 271.85
Magnesium chloride supported DBTDL (20% tin loading) 16400 145.7 390.19
Alumina supported DBTDL
(20% tin loading) 14100 134 291.45

[00101] As noted above, both the supported and unsupported catalyst of the present disclosure gave homopolycarbonate having improved thermal properties.
[00102] Color change or discoloration studies
[00103] The polycarbonates were also tested for color change or discoloration. Table 3 below summarizes the results for both supported and unsupported catalysts. All the parameters were obtained from color spectrophotometer by following ASTM D 2244 standard.
Table 3: Discoloration of polycarbonate
Catalyst Mn(g/gmol) L* a* b* Yellowness Index (YI)
Unsupported catalyst
DBTC 12400 88 -0.02 1.1 2.5
BTA 13700 91 -0.03 2.6 3.8
Supported catalyst
Silica supported DBTDL
(20% tin loading) 13900 90 -0.33 3.1 2.1
Magnesium chloride supported DBTDL
(20% tin loading) 16400 91 -0.14 2.3 4.1
Alumina supported DBTDL
(20% tin loading) 14100 89 -0.21 3.2 3.9

[00104] As can be observed from the above table, the synthesized polycarbonate was almost colorless white powder having good transparency (reflected from L* values).
[00105] Polycarbonates were also prepared using conventionally known titanium catalyst (e.g., titanium isopropoxide), wherein it was observed that the usage thereof gave low molecular weight and low Tg polycarbonate, which was inferior to the polycarbonates prepared using tin catalysts.

ADVANTAGES
[00106] The present disclosure relates to a one-pot synthesis method for preparing polycarbonate, which is economical, bio-based, capable of being easily scaled-up to industrial capacities resulting in high yields of polycarbonate.
[00107] The present disclosure provides polycarbonate(s) having desired properties such as, but not limited to, high thermal stability, high transparency, high scratch resistivity, lower oxygen permeability, color stability and good transparency.
, Claims:1. A one-pot synthesis method for preparing a polycarbonate, the method comprising reacting a dihydroxy compound with a carbonate compound in presence of a transesterification catalyst, characterized in that:
the transesterification catalyst is a tin catalyst selected from the group consisting of: stannous chloride, dibutyl tin dichloride, dibutyl tin diacetate, dibutyl tin oxide, dibutyl tin dilaurate, tin-2-ethylhexanoate, butyl stannoic acid, and butyltin hydroxide-oxide, the weight ratio between the dihydroxy compound and the carbonate compound being in the range of 3.0:2.0 to 1.0:10.0.
2. The method as claimed in claim 1, wherein the tin catalyst is a supported tin catalyst comprising an inorganic support selected from the group consisting of: alumina, magnesium chloride, magnesium oxide, titania, and silica.
3. The method as claimed in any of the claims 1 and 2, wherein the tin catalyst is dibutyl tin dilaurate, butyltin hydroxide-oxide or mixtures thereof.
4. The method as claimed in any one or more of claims 1 to 3, wherein the dihydroxy compound comprises a dianhydrohexitol selected from any or a combination of: isosorbide, isomannide, isoidide, and isomers thereof.
5. The method according to claim 4, wherein the dihydroxy compound further comprises a second dihydroxy compound selected from: an acid, a diol and mixtures thereof, the acid being selected from dodecanedioic acid, adipic acid, hexanedioic acid, isophthalic acid, benzenedicarboxylic acid, teraphthalic acid, naphthalene dicarboxylic acid, and hydroxybenzoic acid, and the diol being selected from 1,4-butane diol, tricyclodecane dimethanol, bis(hydroxymethyl)tricyclodecane, tetramethyl cyclobutanediol, cyclohexanedimethanol, bis(hydroxymethyl)cyclohexane, cyclohexylenedimethanol, bi(cyclohexyl) diol, dicylcohexyl-4,4'-diol, dihydroxybicyclohexyl, ethylene glycol, propylene glycol, hexanediol, resorcinol, catechol, hydroquinol,isomers, polymers, and mixtures thereof.
6. The method as claimed in claim 5, wherein the amount of the second dihydroxy compound ranges from 5 wt.% to 50 wt.% based on the total weight of the dihydroxy compound.
7. The method as claimed in any of the preceding claims, wherein the carbonate compound is selected from:
(a) a dialkyl carbonate represented by the formula R1OCOOR1 or R1OCOOR2, wherein R1 and R2 represents: a linear or branched, substituted or unsubstituted alkyl group having 1 to 10 carbon atoms, or an alicyclic group having 3 to 10 carbon atoms, or a substituted or unsubstituted aralkyl group having 6 to 10 carbon atoms; and
(b) a diaryl carbonate represented by the formula R3OCOOR3 or R3OCOOR4, wherein R3 and R4 represents: an aryl group having 6 to 20 carbon atoms, or a heteroaryl group having 6 to 20 carbon atoms.
8. The method as claimed in any of the preceding claims, wherein the step of reacting comprises:
(a) mixing the dihydroxy compound, the carbonate compound and the transesterification catalyst to obtain a reaction mixture;
(b) subjecting the reaction mixture to transesterification at a temperature ranging between 90°C to 140°C for a duration ranging between 2 hours to 8 hours; and
(c) subjecting the trans-esterified reaction mixture to polycondensation at a temperature ranging between 140°C to 300°C for a duration ranging from 1 hour to 4 hours to obtain the polycarbonate.
9. The method as claimed in any of the preceding claims, wherein the polycarbonate has a number average molecular weight ranging from 5.0 x 103 g/mol to 5.0 x 104 g/mol, and a glass transition temperature ranging between 110°C to 150°C when determined in accordance with ASTM D 3418.
10. A polycarbonate obtained from the method as claimed in any of the claims 1 to 9.
11. A shaped article made from the polycarbonate obtained from the method as claimed in any of the claims 1 to 9.