WO2025109209A1

WO2025109209A1 - Method for the manufacture of polycarbonate resin

Info

Publication number: WO2025109209A1
Application number: PCT/EP2024/083387
Authority: WO
Inventors: Dwairath Dhar; Aaron David Bojarski; David DEL AGUA HERNANDEZ
Original assignee: SABIC Global Technologies BV
Current assignee: SABIC Global Technologies BV
Priority date: 2023-11-24
Filing date: 2024-11-25
Publication date: 2025-05-30
Anticipated expiration: 2026-05-24

Abstract

The present invention relates to a method for preparing an end-capped polycarbonate resin, comprising the steps of: a) melt reacting a dihydroxy compound and a carbonate, optionally in the presence of a transesterification catalyst, thereby forming a polycarbonate in a molten phase having free hydroxyl end-groups and; and b) reacting said polycarbonate in a molten phase with an end-capping reagent to produce the end-capped polycarbonate resin, wherein the end-capping reagent comprises an acid anhydride, wherein said polycarbonate in a molten phase is subjected at least partially to a vacuum after being combined with said end-capping reagent. The present invention further relates to an end-capped polycarbonate resin obtainable by or obtained with such a method. The present invention further relates to a molded article comprising or consisting of this end-capped polycarbonate resin, as well as to a method for the manufacture of such a molded article.

Description

METHOD FOR THE MANUFACTURE OF POLYCARBONATE RESIN

The present invention relates to a method for the manufacture of polycarbonate resin using a melt transesterification process.

Polycarbonate resins are a well-known material and generally exhibits good mechanical and optical properties. Typical applications include optical media carriers, glazing, extruded sheets, lenses and water bottles. Polycarbonate resins are generally manufactured using two different technologies. In a first technology, known as the interfacial technology or interfacial process, phosgene is reacted with one or more bisphenols such as bisphenol A (BPA) in a liquid phase. Another well-known technology for the manufacture of polycarbonate resin is the so-called melt technology, sometimes also referred to as melt transesterification or melt polycondensation technology. In the melt technology, or melt process, a dihydroxy compound, typically a bisphenol, more typically BPA, is reacted with a carbonate, typically a diaryl carbonate, more typically diphenyl carbonate (DPC), in the melt phase. A transesterification catalyst is generally used to reach the desired molecular weight and to advance the polycondensation reaction.

In the interfacial process the polycarbonate is dissolved in a solvent such as methylene chloride, chlorobenzene, or a mixture of both and the process includes several purification steps prior to the polycarbonate resin being isolated and provided in powder or pellet form. This means that typically interfacial polycarbonate resin is substantially free of catalyst or catalyst residues and has a low amount of other impurities.

In the melt process the polycarbonate resin is directly obtained from a final reactor and it is not possible, or at least not economically feasible, to purify the polycarbonate resin. This means that any contaminant that was contained in the raw materials or was generated during the polymerisation process, and further the catalyst or catalyst residues remain present in the obtained polycarbonate resin. Apart from that, a polycarbonate resin obtained by the melt transesterification process is also known to be structurally different from interfacial polycarbonate resin. First of all, melt polycarbonate resin typically has a minimum amount of branching caused by Fries and/or Kolbe-Schmidt rearrangement mechanisms, which branching is generally absent in interfacial polycarbonate resin. Secondly, melt polycarbonate resin typically has a much higher number of phenolic hydroxyl end groups while polycarbonate resin obtained by the interfacial process is typically end-capped and has at most 150 ppm, preferably at most 50 ppm, more preferably at most 10 ppm of phenol hydroxyl end- g roups.

Polycarbonate resins prepared by the reaction of a dihydroxyl compound such as a bisphenol (such as bisphenol A, "BPA") and a carbonate such as a diaryl carbonate (such as diphenyl carbonate, "DPC") in a melt transesterification process generally contain significant levels of uncapped chains (7-50%) as compared to interfacially prepared polycarbonate resins. These uncapped chains can have a significant impact on the resulting properties of polycarbonate resin, and it is therefore desirable in many instances to include an end-capping reagent with a higher capping efficiency than DPC during or after the polymerization reaction which terminates the uncapped chains.

Known end-capping reagents are frequently carbonate or ester derivatives of phenol or even monohydric phenols themselves. Well-known examples are para-cumyl phenol (PCP), 4-tertiary butyl phenol (TBP) and 4-octyl phenol (OP).

US 2003/144456 A1 discloses a method for end-capping polycarbonate resins in a melt transesterification reaction to produce a polycarbonate resin, wherein para-cumyl phenol (PCP) is used as end-capping reagent.

US6706846B2 discloses a method for end-capping polycarbonate resins, comprising the step of processing a mixture comprising a polycarbonate having free hydroxyl end- groups and an end-capping reagent in a melt transesterification reaction to produce a polycarbonate resin, wherein the end-capping reagent comprises a mixture of: (a) at least one species of a symmetrical activated aromatic carbonate, and (b) at least one species of an optionally-substituted phenol, whereby said end-capping reagent reacts with at least some of the free hydroxyl end-groups of the polycarbonate to produce an end-capped polycarbonate resin. There is a need for an end-capped polycarbonate resin which contains a low amount of the starting material dihydroxy compound, such as bisphenol, for example bisphenol A (BPA). There is a further need for an end-capped polycarbonate resin wherein the MW is kept at an acceptable minimum level. There is a further need for a method for manufacturing an end-capped polycarbonate resin with a high end-capping percentage.

Accordingly, it is an object of the present invention to provide a melt transesterification process that results in an improved polycarbonate resin.

It is a further object of the present invention to provide a melt transesterification process that results in a polycarbonate resin which contains a low amount of the starting material dihydroxy compound, such as bisphenol, for example bisphenol A (BPA) while the MW is kept at an acceptable level.

It is a further object of the present invention to provide a method for manufacturing an end-capped polycarbonate resin with a high end-capping percentage.

The foregoing objects are met, at least in part, in accordance with the invention which is directed at a method for preparing an end-capped polycarbonate resin, comprising the steps of: a) melt reacting a dihydroxy compound and a carbonate, optionally in the presence of a transesterification catalyst, thereby forming a polycarbonate in a molten phase having free hydroxyl end-groups and; and b) reacting said polycarbonate in a molten phase with an end-capping reagent to produce the end-capped polycarbonate resin, wherein the end-capping reagent comprises an acid anhydride.

It was surprisingly found that the use of and end-capping reagent comprising an acid anhydride results in a polycarbonate resin having a low amount of residual dihydroxy compound in the polycarbonate resin, and a relatively high molecular weight, as well as a high end-capping percentage. A high end-capping percentage leads to improved hydrostability, color and may even lead to improved mechanical properties such as impact resistance. The present invention further provides a method for preparing an end-capped polycarbonate resin, comprising the steps of: a) melt reacting a dihydroxy compound and a carbonate, optionally in the presence of a transesterification catalyst, thereby forming a polycarbonate in a molten phase having free hydroxyl end-groups and; and b) reacting said polycarbonate in a molten phase with an end-capping reagent to produce the end-capped polycarbonate resin, wherein the end-capping reagent comprises an acid anhydride, wherein said polycarbonate in a molten phase is subjected at least partially to a vacuum after being combined with said end-capping reagent.

The method of the invention comprises b) reacting said polycarbonate in a molten phase with an end-capping reagent to produce the end-capped polycarbonate resin, wherein the end-capping reagent comprises an acid anhydride, wherein said polycarbonate, during step b), is subjected at least partially to a vacuum. By applying vacuum after the polycarbonate is combined with the end-capping reagent (during the reaction of the polycarbonate with the end-capping reagent), volatile side-products of the end-capping reaction and residual dihydroxy compounds can be removed.

End-capping reagent

The end-capping reagent comprises or consists of acid anhydride. For the purpose of the present invention the end-capping reagent preferably comprises at least 50% of acid anhydride. More preferably, the end-capping reagent comprises at least 80 wt.%, such as at least 90 wt.% or 100 wt.% of acid anhydride. The acid anhydride may be one acid anhydrite or a combination of two or more acid anhydrides. In an embodiment, the end-capping reagent may also comprise other compounds than acid anhydride. Examples include phenol, p-tertbutylphenol, p-cumylphenol, octylphenol, nonylphenol and other endcapping reagents well-known in the art.

According to the invention, the acid anhydride of the end-capping reagent reacts with the free hydroxyl end-groups of the polycarbonate made by melt reaction. Accordingly, the end-capped polycarbonate resin prepared by the method of the invention is free of or substantially free of acid anhydride end-groups. The acid anhydride is preferably selected from a symmetric or asymmetric acyclic anhydride, a cyclic anhydride, a dianhydride or a combination thereof. Preferably, the acid anhydride is symmetric.

The acid anhydride may be an acyclic anhydride according to Formula I:

wherein R¹ and R² are independently selected from substituted or unsubstituted, linear or branched C1-C20 hydrocarbon group. In an embodiment, the hydrocarbon group is selected from an alkane, alkene, alkyne or aryl group. In an embodiment, R¹ = R², the anhydride being a symmetric acyclic anhydride.

Preferably, the acyclic anhydride is a symmetrical aromatic carbonate according to formula II:

wherein R³ is selected from hydrogen, halogen, aryl, branched alkane, alkyne, carboxyl, and CN. For example, the phenyl groups may have a halogen substituted on the meta or para position. In another example, the phenyl groups may have a hydrogen, aryl, branched alkane, alkyne, carboxyl, or CN substituted on the para position of the phenyl group. The acyclic anhydride may also have one or more further substitutions on the phenyl-groups, which further substitutions may be the same or different from R³. The acid anhydride may be a cyclic anhydride being an optionally substituted phthalic anhydride according to formula III:

wherein R⁴ is selected from carboxyl and halogen.

For the purpose of the present invention the acid anhydride is preferably selected from

or combinations thereof, wherein each X is independently selected from F, Cl, Br, and I, and n represents an integer between 1 and 10. In an embodiment, the acid anhydride is according to formula 1 ), which is benzoic anhydride. In an embodiment, the acid anhydride has not more than two anhydride functionalities, i.e. the acid anhydride has one anhydride functionality or two anhydride functionalities.

Preferably, the end-capping reagent is added in an amount such that the mole ratio of anhydride in the end-capping reagent to free-hydroxyl end groups is from 0.1 to 10, preferably from 0.5 to 10, preferably from 1.6 to 3.0, even more preferably from 2.0 to 3.0.

The amount of end-capping reagent to be added and mixed is for instance between 0.5 and 10 wt.%, such as between 1 and 4 wt% based on the weight of the polycarbonate. The present inventors found that if the amount of end-capping reagent is too high this may result in by-products such as acids remaining with the polycarbonate causing undesirable effect. It is also for this reason that the present inventors have found that it is beneficial that the end-capping is done in-line prior to the polycarbonate being converted into flakes, powder or pellets. A too low amount will generally not have the desired effect.

For the purpose of the present invention the acid anhydride preferably has a purity of at least 95%, preferably at least 98%.

Raw materials

Commercial melt polycarbonate is typically manufactured on the basis of a dihydroxy compound with a carbonate. The dihydroxy compound may e.g. be a dihydroxy compound having a triphenylamine structure, for example described in EP0610912, but typically is a bisphenol. The carbonate may be a diaryl carbonate or a dialkyl carbonate, typically a diaryl carbonate.

In particular the dihydroxy compound is BPA and the carbonate is DPC. The present invention however is not limited to these starting materials and other bisphenols or carbonates may be used either as such or in combination. For example the present invention also relates to a process wherein the dihydroxy compound comprises BPA and another type of bisphenol. The carbonate is preferably DPC but so-called activated carbonates like for example the ester substituted diaryl carbonates disclosed in US 2008/0004417 may also be used. Preferably the polycarbonate manufactured in accordance with the present invention is obtained by reacting BPA and DPC as the only monomers.

Thus, preferably, the dihydroxy compound comprises or consists of a bisphenol and/or the carbonate comprises or consists of a diaryl carbonate. More preferably, the dihydroxy compound comprises or consists of bisphenol A (BPA) and/or the carbonate comprises or consists of diphenyl carbonate (DPC). Most preferably, the dihydroxy compound consists of bisphenol A (BPA) and the carbonate consists of diphenyl carbonate (DPC).

The melt transesterification process typically does not comprise a step of purification of the obtained polycarbonate similar to a purification step as carried out in the interfacial process. The purity of the raw materials therefore influences the level of quality of the obtained polycarbonate.

It is preferred that the bisphenol, in particular BPA, has a purity of at least 99.3 wt.%, preferably at least 99.5 wt% or at least 99.9 wt%.

Also the diaryl carbonate, in particular DPC, has a purity of at least 98.5 wt.%, preferably at least 98.6 wt% or at least 99.0 wt%.

Catalyst

The catalyst used in the process according to the invention is not limited and any catalyst commonly known for transesterification reactions to manufacture polycarbonate can be used. Thus, the catalyst may be a so-called alpha catalyst, a so-called beta-catalyst or a combination of both.

Suitable examples of alpha-catalyst and beta-catalyst are described in p.15, 1.1 to 28 and p.13, 1.11 to p.14, 1.34 of W02020074983A1 , respectively, which description is incorporated herein by reference.

The alpha catalyst, which is an alkali containing catalyst comprises a source of one or both of alkali ions and alkaline earth ions. The sources of these ions can include alkaline earth hydroxides such as magnesium hydroxide and calcium hydroxide. Sources of alkali metal ions can include the alkali metal hydroxides such as lithium hydroxide, sodium hydroxide, potassium hydroxide, and combinations comprising two or more of the foregoing. Examples of alkaline earth metal hydroxides are calcium hydroxide, magnesium hydroxide, and combinations comprising two or more of the foregoing.

Other possible sources of alkaline earth and alkali metal ions include salts of carboxylic acids (such as sodium acetate) and derivatives of ethylene diamine tetraacetic acid (EDTA) (such as EDTA tetra-sodium salt, and EDTA magnesium disodium salt), as well as combinations comprising at least one of the foregoing. For example, the alkali catalyst can comprise alkali metal salt(s) of a carboxylic acid, alkaline earth metal salt(s) of a carboxylic acid, or a combination comprising at least one of the foregoing. In another example, the alkali catalyst comprises Na2Mg EDTA or a salt thereof.

The alkali catalyst can also, or alternatively, comprise salt(s) of a non-volatile inorganic acid. For example, the alkali catalyst can comprise salt(s) of a non-volatile inorganic acid such as NaH₂PO₃, NaH₂PO₄, Na₂HPO₃, KH₂PO₄, CaH₂PO4, Ca₂HPO4, and combinations comprising two or more of the foregoing. Alternatively, or in addition, the alkali catalyst can comprise mixed alkali metal salt(s) of phosphoric acid, such as NaKHPO4 , CaNaHPO₄, CaKHPO₄, and combinations comprising two or more of the foregoing. The alkali catalyst can comprise KNaHPO4, wherein a molar ratio of Na to K is 0.5 to 2.

The alpha catalyst typically is used in an amount sufficient to provide from

1 x 10'⁸ to 1 x 10'² moles, specifically from 1 x 10'⁷ to 1 x 10'⁴ moles, of metal hydroxide per mole of the dihydroxy compounds employed.

Preferably, the transesterification catalyst used in the method according to the invention comprises an alpha catalyst and the amount of the alpha catalyst is such that 2 x 10'⁷ to 6 x 10'⁷ moles (200 to 600 ppb) of metal hydroxide is provided per mole of the dihydroxy compound. As described elsewhere, step a) of the method of the invention can involve a monomer mixing stage, an oligomerisation stage and a polymerisation stage and the endcapping reagent can be added after the oligomerisation reactors, such as between the last oligomerisation reactor and the first polymerisation reactor, in the first polymerisation reactor, or between the first and the second polymerisation reactor, or in the second polymerisation (which can be the final polymerisation reactor).

It was found that the addition of the end-capping reagent in the final polymerisation reactor results in a decrease in the molecular weight of the final end-capped polycarbonate resin obtained. It was further found that a higher amount of catalyst used prevents such decrease in the molecular weight of the final end-capped polycarbonate resin.

Accordingly, in some preferred embodiments of the invention, the end-capping reagent is added to the final polymerisation reactor and the transesterification catalyst used in the method according to the invention comprises an alpha catalyst and the amount of the alpha catalyst is such that 2 x 10'⁷ to 6 x 10'⁷ moles (200 to 600 ppb) of metal hydroxide is provided per mole of the dihydroxy compound.

Catalyst quencher

Alpha catalysts are transesterification catalysts that are typically more thermally stable than beta catalysts and therefore typically nearly all of the alpha catalyst (e.g., greater than 80 wt.%, specifically greater than 90 wt.%) survives the polymerisation process. As such, this catalyst is available to catalyse additional and generally undesired reactions downstream of the polymerisation process, such as in the extruder or even in any downstream processing step such as for example injection moulding. Typically a catalyst deactivator, or quencher, or quenching agent, is therefore added at a desired stage in the polymerisation process.

Preferably, the process comprises combining said polycarbonate in a molten phase with a quenching agent for deactivating the transesterification catalyst at least in part, wherein said combining with the quenching agent is performed upstream of said combining with end-capping reagent. The quencher preferably comprises a sulfonic acid ester such as an alkyl sulfonic ester of the formula R⁸SO3R⁹ wherein R⁸ is hydrogen, C1-C12 alkyl, Ce-Cis aryl, or C7-C19 alkylaryl, and R⁹ is C1-C12 alkyl, Ce-Cis aryl, or C7-C19 alkyl aryl. Examples of alkyl sulfonic esters include benzenesulfonate, p-toluenesulfonate, methylbenzene sulfonate, ethylbenzene sulfonate, n-butyl benzenesulfonate, octyl benzenesulfonate and phenyl benzenesulfonate, methyl p-toluenesulfonate, ethyl p-toluenesulfonate, n- butyl p-toluene sulfonate, octyl p-toluenesulfonate and phenyl p- toluenesulfonate. The sulfonic acid ester can comprise alkyl tosylates such as n-butyl tosylate.

The quencher can be added in an amount of from 1-10 ppm, based on the total weight of the polycarbonate. The exact amount of quencher depends on the amount of alpha catalyst that is added during the process and should be sufficient to deactivate the remaining catalyst for at least 90%. To that extent the amount of quencher that is added corresponds to 0.1 to 75 times, specifically, 0.5 to 30 times, more specifically 1 to 20 or even more specifically 1 .5 to 10 per the neutralization equivalent of the catalyst used. The quencher may be part of a quencher composition further comprising a liquid carrier such as a solvent, or a solid carrier such as a polymer, preferably polycarbonate.

A preferred quencher is butyl tosylate.

Process/plant

Melt transesterification reaction

The present invention is not limited with respect to how the melt transesterification reaction is carried out and how the plant to carry out the polymerisation is configured. Typically the process involves a monomer mixing stage, an oligomerisation stage and a polymerisation stage. Over the course of the polymerisation the temperature is generally increased and the pressure generally decreased while the molecular weight of the polycarbonate increases.

An increase in temperature is required in view of the increasing viscosity of the polymer being formed and the decreasing pressure is required in order to advance the polymerisation reaction and to effectively remove the by-product of the condensation reaction, typically phenol. The plant for the manufacture of polycarbonate may be part of an integrated site and the BPA and DPC and/or other raw materials may come directly from other plants or units on-site and producing the said monomers either in solid or in molten form. The invention is however not limited to such an embodiment and raw materials such as BPA and DPC may also be obtained from external sources and added to the equipment in the monomer mixing stage using appropriate feeding equipment and upon application of any optional pre-treatment such as melting, filtering, purification, solvent removal etcetera. For example, BPA and DPC may be provided in tanks or bulk containers and fed directly or indirectly to the monomer mixing unit(s).

In the monomer mixing stage the raw materials, typically BPA and DPC, are mixed in a molten state. Optionally an amount of beta catalyst may be added in this stage. The monomer mixing stage is preferably carried out at a temperature of from 100 to 250°C, specifically from 150 to 200°C, more specifically from 160 to 185°C. The pressure in the monomer mixing stage is preferably substantially atmospheric such as from 900 to 1100 mbar.

The alpha catalyst is preferably added downstream of the monomer mixing device and can be added for example upstream of and/or directly to the one or more oligomerisation and/or polymerisation reactors.

The oligomerisation stage is preferably carried out in two steps wherein in a first step the temperature is from 230 to 260 °C and the pressure is from 140 to 250 mbar, and wherein in a second step the temperature is higher than in the first step and from 260 to 290 °C and the pressure is from 10 to 50 mbar. The present invention is however not limited to two steps and any number of between 1-6, such as 2, 3, 4 or 5 oligomerisation steps may be used.

The weight average molecular weight of the oligomer resulting from the oligomerisation stage is preferably at most 20000, preferably from 8000 to 12000 Daltons, determined on the basis of polystyrene standards.

The polymerisation stage is preferably carried out in two steps wherein in a first step the temperature is from 280 to 315 °C and the pressure is from 1 to 5 mbar and wherein in a second step the temperature is from 280°C to 315 °C and the pressure is from 0.3 to 5.0 mbar. The present invention is however not limited to two steps and any number of between 1-6, such as 2, 3, 4 or 5 polymerisation steps may be used.

In an embodiment, the obtained polycarbonate in a molten phase has at least 10 ppm free-hydroxyl end groups, preferably between 10ppm - 1500ppm of free-hydroxyl end groups. The amount of free-hydroxyl end groups can be determined via 31 P NMR.

Reacting polycarbonate in a molten phase with end-capping reagent

The method of adding the end-capping reagent to polycarbonate is not specially limited.

For example, the end-capping reagent may be added to the polycarbonate in a batch reactor or a continuous reactor system. The end-capping reagent may be suitably added to molten polycarbonate and mixed in a static mixer.

In accordance with the invention an end-capping reagent which comprises an acid anhydride is added to a polycarbonate in a molten phase after it has reached a desired molecular weight during the polymerisation, i.e. after the reacting of the dihydroxy compound with the carbonate and the formation of the polycarbonate polymer.

In an embodiment, the end-capping reagent is added after the oligomerisation reactors, such as between the last oligomerisation reactor and the first polymerisation reactor, in the first polymerisation reactor, or between the first and the second polymerisation reactor.

The end-capping reagent may be added in the final polymerisation reactor.

The polycarbonate typically has a weight of 35000-45000 MwPS (g/mol) prior to entering the first polymerization reactor.

At the exit of the final polymerisation reactor the polycarbonate preferably comprises at most 50 ppm, preferably at most 10 ppm residual dihydroxy compound or residual bisphenol A, based on the weight of the polycarbonate. Another possibility is that the end-capping reagent is added at a later stage. After the final polymerisation reactor the molten polycarbonate, having substantially the same temperature as that of the final reactor, can be transported to a unit wherein endcapping reagent and further optional components can be added, e.g. a static mixer and/or a melt mixing device, preferably an extruder.

The end-capping reagent may be added in the melt mixing device, e.g. at a feed section of the melt mixing device, corresponding to the section where the melt coming from the final polymerisation reactor is fed to the extruder. However, the end-capping reagent may also be added at a transfer piping connected to the feed section of the melt mixing device. The end-capping reagent may be added at a single location or at different locations, such as at different sections of the extruder or at the feed section of the melt mixing device and the transfer piping.

In addition to or alternatively to adding end-capping reagent to the final polymerisation reactor or the melt mixing device, end-capping reagent may be added to a static mixer. For example, end-capping reagent compound may be added to a static mixer which receives the molten polycarbonate from the final reactor and then the mixture from the static mixer can be transported to an extruder.

In an embodiment, the end-capping reagent is not added in a melt mixing device, such as in particular an extruder.

When a quencher is added to the polymer melt it is preferred that the end-capping reagent is added prior to quenching of the polycarbonate. Accordingly it is preferred that the end-capping reagent is added upstream of the addition of a catalyst quencher. Thus, in some preferred embodiments, a catalyst quencher is added to the polycarbonate in a molten phase after step b). No catalyst quencher is added upstream of the addition of the end-capping reagent to the polycarbonate in a molten phase obtained by step a). To the polycarbonate in a molten phase obtained by step a), the end-capping reagent is added, vacuum is applied and subsequently the catalyst quencher is applied. The present inventors have found that this configuration is preferred for maintaining the catalyst active and make use of its reactivity for maintaining the MW at a desired level. In accordance with the invention, the polycarbonate in a molten phase is subjected at least partially to a vacuum after the stream is combined with said end-capping reagent. This may be performed by a vacuum means provided in the first or second polymerisation reactor or in the melt mixing device. The vacuum may e.g. be in the range of 0.5 - 5 mbar, for example 1 to 3 mbar. This is particularly advantageous because the application of vacuum after combining (and mixing) the polycarbonate in a molten phase with the end-capping reagent can be used to influence the viscosity and the MW of the polycarbonate resin. When the vacuum is applied directly after (in the same vessel as) combining (and mixing) the polycarbonate in a molten phase with the end-capping reagent this ensures sufficient residence time and activity of the catalyst. Vacuum also allows for removal of volatile side-products of the end-capping reaction such as acids generated from anhydrides. It will be appreciated that when vacuum is applied in the melt mixing device, only part of the polycarbonate obtained by step b) may be under vacuum.

Additives may optionally be added e.g. to the melt mixing device and/or the static mixer. Suitable examples of the optional additives include one or more of an impact modifier, flow modifier, filler, reinforcing agent (e.g., glass fibers or talc), antioxidant, heat stabilizer, light stabilizer, UV light stabilizer and/or UV absorbing additive, plasticizer, lubricant, release agent, in particular glycerol monostearate, pentaerythritol tetra stearate, glycerol tristearate, stearyl stearate, antistatic agent, antifog agent, antimicrobial agent, colorant (e.g., a dye or pigment), flame retardant either or not combined with an anti-drip agent such as polytetrafluoroethylene (PTFE) or PTFE-encapsulated styrene-acrylonitrile copolymer. The present invention is not limited in terms of the type and amount of additives and an embodiment is possible wherein none of these additives exemplified above is added.

Although a branching agent may be added to the mixture, it is preferred that no branching agent is added.

Melt filter

Preferably, the polycarbonate in a molten phase is passed through a melt filter after the stream is combined with said end-capping reagent. A melt filter has the function of removing any particulate matter or gels from the stream. The melt filter may have a pore size of for example 2.5-60 micrometer.

Finally the polycarbonate in a molten phase is passed through a die into one or more strands which are then cooled and cut into pellets.

Figure 1 is a schematic and non-limiting example of a plant to manufacture polycarbonate in accordance with the invention;

BPA and DPC are added as streams A and B1 respectively to monomer mixing device 10. The DPC to BPA ratio in the monomer mixing device is kept fixed. A beta catalyst is added to monomer mixing device 10 via stream C. Monomer mixing device 10 is equipped with a suitable stirrer so as to guarantee a homogeneous mixture in the device. Monomer mixing device 10 is typically maintained at a temperature of from 160 to 185°C and at a pressure of 200-300 mbar above atmospheric pressure. The stream exiting monomer mixing device 10 is fed to a first oligomerisation reactor 20. For reasons of process flexibility an additional amount of DPC may be added as stream B2. An alpha catalyst is added as a stream D. This monomer mixture is then fed to oligomerisation reactor 20 of the oligomerisation stage.

Oligomerisation reactor 20 operates at a temperature of from 230 to 260°C and a pressure of from 140 to 250 millibar. An overhead stream comprising phenol byproduct and optionally monomers or other low molecular weight reaction products is removed via stream 70 and fed to column 50, which separates the phenol from the stream. The phenol is then removed via top stream E for further purification and/or use, while the bottom stream is fed back to reactor 20 as stream 71. In an alternative embodiment the stream 70 is purified elsewhere and there is no recycle of material to the oligomerisation reactor(s) 20, 21.

The mixture exiting reactor 20 is fed to a second oligomerisation reactor 21 for further reaction. Second oligomerisation reactor 21 operates at temperature of from 260 to 290°C and a pressure of from 10 to 50 millibar. Phenol byproduct is removed from second reactor 21 as a stream E. Oligomerisation reactors 20 and 21 constitute the oligomerisation stage, resulting in a stream of polycarbonate oligomer which is fed to first polymerisation reactor 30 and then to second polymerisation reactor 31. Reactor 30 operates at a temperature of from 280 to 315°C and a pressure of 1 to 5 millibar. The stream from the first polymerisation reactor 30 is then fed to a second polymerisation reactor 31 that operates at temperature of from 280 to 315°C and a pressure of from 0.3 to 5.0 millibar. The temperature in reactor 31 is generally higher than in reactor 30 and the pressure in reactor 31 is generally lower than the pressure in reactor 30. Similar to the oligomerisation stage phenol by-product is removed from the reactors 30 and 31. Polymerisation reactors 30 and 31 together constitute the polymerisation stage.

The polymer exiting second polymerisation reactor 31 is fed to extruder 40.

An amount of end-capping reagent may be added via feed 16a at the feed section of polymerisation reactor 30 or feed 16b at the feed section of polymerisation reactor 31 . Alternatively the end-capping reagent may also be added via feed 16c at the feed section of the extruder 40, or injected into the melt stream coming from reactor 31 in the transfer piping and close to the feed section of the extruder.

Optionally, other additives are added to the extruder, indicated with I. Additives may alternatively be added at the feed section of the extruder.

Catalyst quencher is also added to the extruder in order to deactivate the catalyst in the molten polycarbonate. Alternatively, the catalyst quencher may be added to the second polymerisation reactor 31. In that case, it is preferred that the end-capping reagent is added in the first polymerisation reactor 30. For the avoidance of doubt it is noted that the position for addition of catalyst quencher is not limited.

The stream extruded from the extruder 40 is passed through a melt filter 60 and then extruded to strands, cooled, and cut to pellets indicated with J.

It is noted that while Figure 1 illustrates polymerisation reactors 30 and 31 to be horizontal polymerisation units, these reactors may likewise each independently be vertical reactors, such as for example wire wetting fall polymerisation units. The process indicated in Figure 1 is shown as a single production line. It is however possible that at any point during the process the line is split into two or more parallel lines wherein each line operates at the same or different conditions including monomer mixture composition, temperature, pressure residence time etc. By way of example the stream exiting oligomerisation reactor 21 may be split into two or more different streams after which each stream is polymerised in one or more polymerisation reactors using, by way of example, different conditions resulting in the parallel manufacture of different grades of polycarbonate. Another possibility is to split the stream exiting the final polymerisation reactor 31 and then to feed the polycarbonate stream to different extruders. The parallel operation of (parts of the) production lines as shown in Figure 1 is known to a skilled person.

Apart from the specific configuration shown in Figure 1 the polycarbonate may be manufactured under one or more of the following preferred conditions.

It is preferred that the monomer mixing stage comprises addition of a beta catalyst wherein the beta catalyst is a quaternary ammonium or quaternary phosphonium compound or a mixture thereof.

It is preferred that the oligomerisation stage consists of preparing a polycarbonate oligomer in two oligomerisation reactors and wherein the polymerisation stage consists of preparing the polycarbonate in two polymerisation reactors.

In a preferred embodiment of method of the invention the bisphenol is BPA, the diaryl carbonate is DPC, a beta catalyst is added in the monomer mixing stage and an alpha catalyst is added prior to feeding the monomer mixture prepared in the monomer mixing device to the first oligomerisation reactor. In a preferred embodiment the bisphenol is BPA, the diaryl carbonate is DPC, the alpha catalyst is NaKHPC and the beta catalyst is tetra-butyl phosphonium acetate.

The method of the invention is preferably a continuous method.

End-capped polycarbonate resin The end-capped polycarbonate resin manufactured in accordance with the invention has a lower amount of dihydroxy compound and/or a similar or higher molecular weight and/or a higher end-cap level compared to an otherwise identical polycarbonate resin manufactured under otherwise identical conditions yet without the addition of an endcapping reagent in accordance with the invention.

For the avoidance of doubt it is noted that the polycarbonate obtained with the method of the present invention does not contain polycarbonate chains which contain acid anhydride functionality originating from the endcapping reagent. Thus, the acid anhydride functionality of the endcapping reagent reacts with the hydroxyl (end) groups of the polycarbonate and is accordingly not incorporated into the polymer chain as such.

The end-capped polycarbonate resin may have a weight average molecular weight from e.g. 30,000 to 70,000 g/mol, for example 30,000 to 50,000 g/mol or 50,000 to 70,000 g/mol, as determined using GPC on the basis of polystyrene standards.

In some embodiments, the end-capped polycarbonate resin has a weight average molecular weight of at least 36,000 g/mol, as determined using GPC on the basis of polystyrene standards.

Preferably, the end-capped polycarbonate resin has an endcap level of at least 60%, more preferably from 65 to 95%, even more preferably 70 to 95%, wherein the endcap level is defined as the percentage of polycarbonate chain ends which are not hydroxyl groups. Thus a polycarbonate resin having and endcap level of 60% means that the polycarbonate has 40% of chain ends that are phenolic OH end groups, usually resulting from the bisphenol A monomer. The other 60% of end groups do not contain an OH end group and may be phenolic (usually originating from the diphenylcarbonate) or correspond to the end capping reagent molecule(s).

The endcap level is calculated with the following formula

%EC = 100 - ((ppmOH x Mn)/340000) wherein %EC is the endcap level, ppmOH is the amount of hydroxyl end groups in parts per million by weight and Mn is the number average molecular weight of the polycarbonate based on polycarbonate standards.

Thus, the endcap level is defined as the mole percentage of end-groups of the endcapped polycarbonate resin that is not a hydroxyl group and can be calculated from the amount of terminal OH groups in the end-capped polycarbonate resin and the number average molecular weight (Mn).

The amount of chain ends that are end-capped with the end-capping reagent is preferably at least 40% on the basis of the total amount of end-groups.

The end-capped polycarbonate resin may have a degree of branching resulting from Fries (or Kolbe-Schmidt) rearrangement reactions of from 200 - 4000 ppm, for example 500 to 2000 ppm. The degree of branching is commonly referred to as amount of Fries branching. Methods for determining the amount of Fries branching are known to the skilled person and generally include the methanolysis of the polycarbonate resin followed by HPLC chromatography to identify the total amount of Fries structures. In addition, NMR techniques can be used to determine the type and amount of the branching structures, such as the respective amounts of linear and branched Fries structures.

It will be appreciated that some amounts of residual materials used during the method for the manufacture for the end-capped polycarbonate resin may remain in the endcapped polycarbonate resin obtained by the method. Accordingly, term “polycarbonate resin” as used herein is understood to include not only the polycarbonate molecules but also the residual materials.

In some embodiments, the dihydroxy compound is bisphenol A and the amount of residual bisphenol A in the end-capped polycarbonate resin is at most 50 ppm, preferably at most 25 ppm, more preferably at most 10 ppm, most preferably at most 5 ppm based on the weight of the end-capped polycarbonate resin. In some embodiments, the amount of hydroxyl end-groups in the polymer chain is at most 1100 ppm, preferably at most 500 ppm, more preferably at most 450 ppm based on the weight of the end-capped polycarbonate resin.

In an embodiment, at least 70%, preferably 80-90%, of the added end-capping reagent is incorporated into the end-capped polycarbonate resin.

The amount of residual dihydroxy compound in the end-capped polycarbonate resin may be determined by the following method.

Sample preparation:

Dissolve 0.5 gram of polycarbonate in 5 ml Dichloromethane (DCM) and precipitate the polycarbonate with 10 ml Methanol. Filter the solution into a LC sampler vial.

Analytical Technique:

Liquid Chromatography-Diode Array Detector (HPLC-DAD).

Column: Zorbax Eclipse XDB-C18 4.6 x 75 mm 3.5 urn.

Column Temperature: 35°C.

Wavelengths: 280nm (BPA)

Polycarbonate composition

The present invention further provides a polycarbonate composition comprising the end-capped polycarbonate resin and additives.

Suitable examples of the additives include one or more of an impact modifier, flow modifier, filler, reinforcing agent (e.g., glass fibers or talc), antioxidant (primary antioxidant and/or secondary antioxidant), heat stabilizer, light stabilizer, UV light stabilizer and/or UV absorbing additive, plasticizer, lubricant, release agent, in particular glycerol monostearate, pentaerythritol tetra stearate, glycerol tristearate, stearyl stearate, antistatic agent, antifog agent, antimicrobial agent, colorant (e.g., a dye or pigment), flame retardant either or not combined with an anti-drip agent such as polytetrafluoroethylene (PTFE) or PTFE-encapsulated styrene-acrylonitrile copolymer. The present invention is not limited in terms of the type and amount of additives. In some embodiments, the polycarbonate composition comprises at least one of a primary antioxidant and a secondary antioxidant.

In some embodiments, the polycarbonate composition consists of the polycarbonate according to the invention and at least one of a primary antioxidant and a secondary antioxidant.

The present invention further provides a thermoplastic composition comprising the end-capped polycarbonate resin according to the invention or the polycarbonate composition according to the invention and at least one further polymer, preferably selected from the group consisting of polycarbonate - polyorganosiloxane copolymers, polycarbonate-polyester copolymers, polyesters, polyolefins, acrylonitrile/butadiene/styrene copolymer, methyl methacrylate/butadiene/styrene copolymer, styrene/butadiene/styrene copolymer (SBS), styrene/ ethylene-butylene /styrene copolymer (SEBS), styrene/ ethylene-propylene /styrene copolymer (SEPS) styrene/acrylonitrile copolymer (SAN), acrylonitrile/styrene/acrylonitrile copolymer (ASA), polybutylene terephthalate (PBT), polyethylene terephthalate (PET), unsaturated polyester (UPES), polyamide (PA), thermoplastic urethane (TPU), polystyrene (PS), high impact polystyrene (HIPS), polyvinyl chloride (PVC), polyetherimides, polysulfones. The amount of the polycarbonate may e.g. be at 5 to 95 wt%, 50 to 95 wt% or 55 to 95 wt% with respect to the thermoplastic composition.

The thermoplastic composition according to the invention may be made e.g. by meltmixing the end-capped polycarbonate resin according to the invention or the polycarbonate composition according to the invention and the at least one further polymer.

The present invention further provides a molded article comprising or consisting of the end-capped polycarbonate resin according to the invention, the polycarbonate composition according to the invention or the thermoplastic composition according to the invention.

The present invention further provides a method for the manufacture of a molded article comprising molding the end-capped polycarbonate resin according to the invention, the polycarbonate composition according to the invention or the thermoplastic composition according to the invention.

The present invention will now be further elucidated on the basis of the following nonlimiting examples.

The end-capped polycarbonate resin was continuously produced using an apparatus as schematically shown in Figure 1.

BPA and DPC were introduced in a monomer mixing device which was kept at a temperature of 170 °C at a pressure of about 1050 mbar. 50 micromoles of tetra butyl phophonium acetate (TBPA) per mole of BPA was also added as a beta catalyst.

The monomer mix was then introduced in the first oligomerisation reactor operating at a temperature of 250-270°C and a pressure of 155-190 mbar. The initial DPC/BPA ratio (molar ratio) was adjusted with additional DPC to 1.020-1.045 and an amount of NaKHPC as alpha catalyst was added. The carbonate oligomer formed in the first oligomerisation reactor was fed to the second oligomerisation reactor operating at a temperature of 275-295 °C and a pressure of 10-37 mbar.

The so formed carbonate oligomer was then introduced to a first polymerisation reactor operating at a temperature of 295-300 °C and pressure of 2.0-4.0

An amount of 30 g. of the produced material from the first polymerisation reactor was combined with the end-capping reagent, i.e. the anhydride (solid powder), such that the molar ratio of the anhydride to OH content in the polycarbonate is maintained at 1 :1 or 3:1. The composition was mixed in a glass reactor and heated to 300°C for 25 minutes while maintaining the pressure of the reaction vessel at 1 mBar. The polycarbonate mixture was isolated after the reaction and characterized using standard analytical techniques such as Gel Permeation Chromatography (GPC) for MW (using polystyrene standard), Fries branching content by HPLC (using Fries standard) and unreacted BPA residuals by HPLC. NMR spectroscopy was used to determine the incorporation of the anhydride in the backbone of polycarbonate. The structure of the resulting end-capped polycarbonate resin was analysed by NMR.

The amount of the residual BPA was measured by HPLC.

The amount of residual benzoic acid was measured by HPLC.

MW was determined using GPC on the basis of polystyrene standards.

The endcap level %EC was determined as

%EC = 100 - (ppmOH X Mn)/340000) wherein %EC is the endcap level, ppmOH is the amount of hydroxyl end groups in parts per million by weight and Mn is the number average molecular weight of the endcapped polycarbonate resin based on polycarbonate standards.

The amount of hydroxyl end groups was determined by 31 P NMR. For this, 200 mg of PC sample was dissolved in 2 ml CDCI3 (deuterated chloroform) solvent containing Cr(acac)3 and mesitol as internal standard. A few drops of 1 ,2-phenlyene phosphorochloridite (PPC) were added and mixed together which resulted in derivatization of OH end-groups. The NMR spectra have been recorded on an Agilent 400 MHz spectrometer equipped with a probe operating at 25°C.

The amount of the specific end-capping reagent comprising acid anhydride which was incorporated into the end-capped polycarbonate resin was determined by 1 H NMR spectroscopy. 1 H NMR spectra in CDCI3 was used to calculate the incorporation of the end-capping reagent. The concentrations were calculated based on the amount of BPA or on internal standard mesitol. The mass of the new end-cap was taken as follows: 121. g / mol in the case of end-capping reagent derived from benzoic anhydride and 85.08 g / mol in the case of end-capping reagent derived from methacrylic anhydride.

121.1 g/mol

85.08 g / mol

In addition, a percentage is calculated of the amount of ‘new end-cap’, meaning the percentage of end-capping that is generated by the addition of the end-capping reagent comprising acid anhydride. In general, part of the end-capping is phenyl carbonate end-capping generated by the formulation itself (in the case of these Examples by BPA + DPC), and an additional part is generated by the addition of the end-capping reagent. The ‘New end-cap’ percentage specifies the latter part.

Table 1 provides an overview of the different examples. CE1 is a comparative example, wherein the same protocol is followed but no end-capping reagent is added.

Table 1 : example overview

Table 2 summarizes the obtained results. The results include the weight averaged molecular weight of the end-capped polycarbonate resin based on polystyrene standards (MwPS), the number averaged molecular weight of the end-capped polycarbonate resin based on polystyrene standards (MnPS), and the number averaged molecular weight of the end-capped polycarbonate resin based on polycarbonate standards (MnPC). The polydispersity index (PDI) can be used as measure of broadness of molecular weight distribution: the larger the PDI, the broader the molecular weight. The PDI is the ratio of the MwPS and the MnPS. The amount of hydroxyl end-groups (OH), the endcap level (Total EC%, calculated as shown above), the amount of residual BPA, the amount of end-capping reagent incorporated into the end-capped polycarbonate resin, and the new endcap level (New End-cap %, described above) are also shown in Table 2.

Table 2: results

It should be noted that the amount of residual benzoic acid was measured but was below detection limit for all (comparative) examples.

It can be seen from Table 2 that the use of an end-capping reagent comprising an acid anhydride leads to a higher end-capping percentage then when no anhydride is used, and that the amount of residual dihydroxy compound (BPA) has reduced significantly. These effects can be seen most strongly when benzoic anhydride is used in a 3:1 ratio to the amount of hydroxyl end-groups. The last two columns of Table 2 confirm that the additional end-capping is indeed achieved by the addition of the end-capping reagent.

At the same time it can be seen from Table 2 that the MW of the obtained end-capped polycarbonate resin is still relatively high, and is kept at an acceptable level compared to the comparative example without acid anhydride.

Table 3 shows the amount of incorporation of the end-capping reagent into the chain of the polycarbonate by the reaction of the acid anhydride with the hydroxyl end- groups. The end-capped polycarbonate resin of examples E5-E7 were continuously produced using an apparatus as schematically shown in Figure 1 and as described above. The flow rate of polycarbonate was for all these examples E5-E7 was 65 kg/h. For all three examples E4-E6, the end-capping reagent is benzoic anhydride. Examples E4-E6 differ in the amount of end-capping reagent added, and thus in the molar ratio anhydride : hydroxyl groups. For E5-E7 the amount of hydroxyl end-groups (OH) was determined via FTIR spectroscopy. For this, 500 mg of PC sample was dissolved in 10 ml methylene chloride. Fresh dried molecular sieves were added to the solution in order to remove the moisture (H2O) content that may interfere with the response of the OH stretching frequency in the FT-IR. The FT-IR spectra have been recorded on a Perkin Elmer Spectrum 100 spectrometer.

The amount of the specific end-capping reagent which was incorporated into the endcapped polycarbonate resin ("Endcapper incorporation") was determined by 1 H NMR spectroscopy. Then, the new endcap level (New End-cap %, described above) was determined (not shown) and from this the percentage of incorporation of the added benzoic anhydride into the polycarbonate chain was calculated.

Table 3:

It can be seen from Table 3 that a high amount of end-capping agent can be incorporated into the end-capped polycarbonate resin by the method according to the present invention.

Further end-capped polycarbonate resins were continuously produced using an apparatus as schematically shown in Figure 1. Benzoic acid were added between the first and second polymerisation reactors 30 and 31 in various amounts as shown in Table 4. NaKHPC>4 as alpha catalyst was added at the inlet of the first oligomerisation reactor 10 in various amounts as shown in Table 4.

Table 4

It can be understood that the addition of the benzoic acid in the final polymerisation reactor leads to a higher end-capping percentage than when no anhydride is used, but also to a decrease in the molecular weight of the final end-capped polycarbonate resin obtained, see CE11 vs E12.

It can further be understood that a higher amount of catalyst used reduces such decrease in the molecular weight of the final end-capped polycarbonate resin, see CE11 vs E12 vs E13. The higher amount of benzoic acid leads to a higher end-capping percentage, see E13-E16.

Claims

C L A I M S

1. Method for preparing an end-capped polycarbonate resin, comprising the steps of: a) melt reacting a dihydroxy compound and a carbonate, optionally in the presence of a transesterification catalyst, thereby forming a polycarbonate in a molten phase having free hydroxyl end-groups and b) reacting said polycarbonate in a molten phase with an end-capping reagent to produce the end-capped polycarbonate resin, wherein the end-capping reagent comprises an acid anhydride, wherein said polycarbonate in a molten phase is subjected at least partially to a vacuum after being combined with said end-capping reagent.

2. Method according to claim 1 , wherein the acid anhydride is selected from a symmetric or asymmetric acyclic anhydride, a cyclic anhydride, a dianhydride or a combination thereof.

3. Method according to claim 2, wherein the acid anhydride is an acyclic anhydride according to Formula I:

wherein R¹ and R² are independently selected from substituted or unsubstituted, linear or branched C1-C20 hydrocarbon group.

4. Method according to claim 3, wherein the acyclic anhydride is a symmetrical aromatic carbonate according to formula II:

wherein R³ is selected from hydrogen, halogen, aryl, branched alkane, alkyne, carboxyl, and CN.

5. Method according to claim 2, wherein the acid anhydride is a cyclic anhydride being an optionally substituted phthalic anhydride according to formula III:

wherein R⁴ is selected from a carboxyl group and halogen.

6. Method according to claim 1 or 2, wherein the acid anhydride is selected from the following formulas:

or combinations thereof, wherein each X is independently selected from F, Cl, Br, and I, and n represents an integer between 1 and 10, preferably wherein the acid anhydride is according to formula 1 ), being benzoic anhydride.

7. Method according to any of the preceding claims, wherein the endcapping reagent is added in an amount such that the mole ratio of anhydride in the end-capping reagent to free-hydroxyl end groups is 0.1 to 10, preferably from 0.5 to 10, preferably from 1.6 to 3.0, even more preferably from 2.0 to 3.0.

8. Method according to any of the preceding claims, wherein the endcapping reagent is added in a vessel, which vessel comprises vacuum means by which the polycarbonate in a molten phase combined with the acid anhydride is at least partially subjected to a vacuum in the range of from 0.5 - 5 mbar, for example 1 to 3 mbar.

9. Method according to any of the preceding claims, wherein a catalyst quencher is added to the polycarbonate in a molten phase after step b).

10. Method according to any of the preceding claims, wherein the transesterification catalyst comprises an alpha catalyst and the amount of the alpha catalyst is such that 200-600 mol ppb of metal hydroxide is provided per mole of the dihydroxy compound.

11. End-capped polycarbonate resin obtainable by or obtained with the method of any one or more of claims 1-10, preferably wherein the amount of residual dihydroxy compound or residual bisphenol A in the end-capped polycarbonate resin is at most 50 ppm, preferably at most 10 ppm based on the weight of the end-capped polycarbonate resin.

12. End-capped polycarbonate resin obtainable by or obtained with the method of any one or more of claims 1-10, wherein the amount of hydroxyl-end groups in the polymer chain is at most 1100 ppm, preferably at most 500 ppm, more preferably at most 450 ppm based on the weight of the polycarbonate.

13. End-capped polycarbonate resin according to claim 11 or 12, wherein the end-capped polycarbonate resin a weight average molecular weight of at least 36,000 g/mol, as determined using GPC on the basis of polystyrene standards.

14. End-capped polycarbonate resin according any of claims 11-13, wherein the end-capped polycarbonate resin has an amount of fries branching of 200- 4000 ppm, preferably 500-2000 pmm.

15. Molded article comprising or consisting of the end-capped polycarbonate resin of any of claims 11-14.

16. Method for the manufacture of a molded article comprising molding the end-capped polycarbonate resin according to any of claims 11-14.