EP3692090A1 - Improved method of modifying a polycarbonate during a melt polymerization - Google Patents

Abstract

In an embodiment, a method for the manufacture of a melt polycarbonate, comprises melt polymerizing a feed stream in a final polymerization unit to form a polycarbonate stream comprising a polycarbonate; controlling a scission stream flowrate of a chain scission stream comprising the chain scission agent; and mixing the chain scission stream and the polycarbonate stream to form an adjusted stream comprising a reduced molecular weight polycarbonate.

Description

IMPROVED METHOD OF MODIFYING A POLYCARBONATE

DURING A MELT POLYMERIZATION

CROSS-REFERENCE TO RELATED CASE

This application claims the benefit of European Application Serial No. 17382666.0 filed October 5, 2017. The related application is incorporated herein in its entirety by reference.

BACKGROUND

[0001] Different commercial applications of polycarbonate rely on different polycarbonate grades. One of the most critical parameters in determining the grade of a polycarbonate is viscosity, as polycarbonate grades often have very narrow viscosity specification windows that allow the respective polycarbonate grades to maintain their desired performance properties. Therefore, improved production processes that are capable of achieving a polycarbonate with both accuracy for obtaining a specific viscosity and precision with a minimal deviation from the target viscosity are desired.

BRIEF SUMMARY

[0002] Disclosed herein is a method for the manufacture of a melt polycarbonate.

[0003] In an embodiment, a method for the manufacture of a melt polycarbonate, comprises melt polymerizing a feed stream in a final polymerization unit to form a polycarbonate stream comprising a polycarbonate; controlling a scission stream flowrate of a chain scission stream comprising the chain scission agent; and mixing the chain scission stream and the polycarbonate stream to form an adjusted stream comprising a reduced molecular weight polycarbonate.

[0004] The above described and other features are exemplified by the following figures, detailed description, and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0005] The Figures are exemplary embodiments wherein the like elements are numbered alike. The Figures are non-limiting exemplary embodiments, which are provided to illustrate the present method.

[0006] FIG. 1 is an illustration of an embodiment of a method of adding a chain scission agent based on a measured viscosity of the polycarbonate stream 12; [0007] FIG. 2 is an illustration of an embodiment of a method of adding a chain scission agent based on a measured viscosity of the adjusted stream 18;

[0008] FIG. 3 is an illustration of an embodiment of a method of adding a chain scission agent based on a differential between a measured viscosity of the polycarbonate stream 12 and the adjusted stream 18;

[0009] FIG. 4 is an illustration of an embodiment of a method of adjusting the pressure in a polymerization unit based on a measured viscosity of the polycarbonate stream 8; and

[0010] FIG. 5 is a graphical illustration of the viscosity change with time of Examples

1-3.

DETAILED DESCRIPTION

[0011] During the melt polymerization of polycarbonate, minor changes in the polymerization conditions including monomer flow rate, catalyst flow rate, reactor temperatures, reactor pressures, and plant throughput can significantly affect the molecular weight of the resultant polycarbonate. These changes can result in the production of polycarbonate that does not meet the target specifications, often referred to as off-spec polycarbonate. In order to avoid the production of off-spec polycarbonate, pressure control feedback loops of the polymerization units have been employed. These pressure control feedback loops rely on complex mathematical functions that take into consideration the pump discharge pressure, pump speed, and product temperature to estimate the viscosity and then adjust the pressure of a polymerization unit based on the estimated viscosity. For example, if the estimated viscosity is lower than a target viscosity, then the pressure in the

polymerization unit can be decreased (i.e., a deeper vacuum can be set). This decrease in pressure in the polymerization of bisphenol A polycarbonate, for example, increases the amount of phenol by-product produced, thus driving the polymerization reaction forward to result in a polycarbonate with an increased molecular weight as observed by an increase in polycarbonate viscosity. Using this method though, it is difficult to accurately obtain the target viscosity due to the use of a non-universal correlation that has inherent errors associated with laboratory analysis and inherent errors in the related variables (i.e., pump performance, temperature precision, etc.) that affects correlation reliability. Furthermore, when a viscosity change is desired, using this method, it is difficult to obtain a target molecular weight with minimal deviation due to the residence time in the final polymerization unit and the response time, often of more than an hour, associated with how long it takes for the system to respond to the pressure change.

[0012] A new method for modifying the viscosity of melt polycarbonate was developed to obtain a viscosity with improved consistency and improved response time. The method comprises controlling a scission stream flowrate of a chain scission stream

comprising a chain scission agent using a feedforward loop or a feedback loop based on the viscosity of the polycarbonate. The controlling can comprise determining an upstream viscosity, an upstream temperature, and optionally one or both of an upstream flowrate and an endcap level of the polycarbonate stream and controlling the scission stream flowrate based on the upstream viscosity, the upstream temperature, and optionally on the upstream flow rate and the endcap level. Additionally or instead of, the controlling can comprise determining a downstream viscosity and a downstream temperature of the adjusted stream and controlling the scission stream flowrate based on the downstream viscosity and the downstream temperature. Using at least one of these control methods can advantageously allow for a reduction in the viscosity variability during the polymerization process as the amount of chain scission agent added can be easily and precisely adjusted.

[0013] It is noted that as used herein, with reference to the controlling, "upstream" parameters are of the polycarbonate stream at a location upstream of the location of the addition of the chain scission agent. For example, a final polymerization unit can be in fluid communication with an extruder via a conduit and a mixing element can be located along the length of the conduit and the upstream parameters can refer to the parameters of the stream in between the final polymerization unit and the mixing element. Likewise, it is noted that as used herein, with reference to the controlling, "downstream" parameters are of the adjusted stream at a location downstream of the location of the addition of the chain scission agent. For example, a final polymerization unit can be in fluid communication with an extruder via a conduit and a mixing element can be located along the length of the conduit and the downstream parameters can refer to the parameters of the stream in between the mixing element and the extruder.

[0014] The present method can further allow for a reduction in the changeover time between polycarbonate grades. For example, the process can involve producing a high molecular weight polycarbonate in the polymerization system and, without changing the processing conditions, obtaining a polycarbonate with a reduced molecular weight by adding a chain scission agent. For example, a melt polymerization can operate at a set of conditions (for example, at least one of temperature, pressure, residence time, catalyst concentration, or monomer flow rate, e.g., of temperature, pressure, residence time, and catalyst concentration) that remain within 5%, or 1% of their set values prior to, during, and after the molecular weight adjustment and only the flowrate of the chain scission agent can be changed and adjusted as needed to help ensure a consistent product.

[0015] The "polycarbonate" as used herein is derived from a carbonate compound and a dihydroxy compound such as a bisphenol and can have repeating structural carbonate units of formula (1)

O

R¹— O C O (1)

in which the R¹ groups contain aliphatic, alicyclic, and/or aromatic moieties (e.g., greater than or equal to 30 percent, or greater than or equal to 60 percent of the total number of R¹ groups can contain aromatic moieties and the balance thereof are aliphatic or alicyclic). Optionally, each R¹ can be a C₆-3o aromatic group that can contain at least one aromatic moiety. R¹ can be derived from the bisphenol.

[0016] The carbonate compound can comprise a diaryl carbonate ester, for example, diphenyl carbonate or an activated diphenyl carbonate having electron- withdrawing substituents on each aryl, for example, at least one of bis(4-nitrophenyl)carbonate, bis(2- chlorophenyl)carbonate, bis(4-chlorophenyl)carbonate, bis(methyl salicyl)carbonate, bis(4- methylcarboxylphenyl) carbonate, bis(2-acetylphenyl) carboxylate, or bis(4-acetylphenyl) carboxylate. The carbonate compound can comprise diphenyl carbonate. The diaryl carbonate ester can be free of an activated diphenyl carbonate having electron- withdrawing substituents on each aryl. For example, the diaryl carbonate ester can be free of bis(4- nitrophenyl)carbonate, bis(2-chlorophenyl)carbonate, bis(4-chlorophenyl)carbonate, bis(methyl salicyl)carbonate, bis(4-methylcarboxylphenyl) carbonate, bis(2-acetylphenyl) carboxylate, and bis(4-acetylphenyl) carboxylate. The diaryl carbonate ester can be free of bis(methyl salicyl)carbonate. As used herein, "can be free of refers to none of the compounds being added in the melt polymerization, for example, less than or equal to 10 ppm, for example, 0 ppm of the compound being present.

[0017] The bisphenol can comprise a bisphenol of the formula HO-R^OH, wherein the R¹ group can contain an aliphatic, an alicyclic, or an aromatic moiety. For example, the bisphenol can have the formula (2)

HO-A -Y -A^OH (2) wherein each of A 1 and A2 is a monocyclic divalent aromatic group and Y 1 is a single bond or a bridging group having one or more atoms that separate A 1 from A 2. One atom can separate A¹ from A².

[0018] The bisphenol can have the formula 3)

wherein R^a and R^b are each independently a halogen, C_1-12 alkoxy, or C_1-12 alkyl; and p and q are each independently integers of 0 to 4. It will be understood that R^a is hydrogen when p is 0, and likewise R^b is hydrogen when q is 0. Also in formula (3), X^a is a bridging group connecting the two hydroxy-substituted aromatic groups, where the bridging group and the hydroxy substituent of each C₆ arylene group are disposed ortho, meta, or para (specifically, para) to each other on the C₆ arylene group. The bridging group X^a can be single bond, -0-, - S-, -S(O)-, -S(0)₂-, -C(O)-, or a C_1-18 organic bridging group. The C_1-18 organic bridging group can be cyclic or acyclic, aromatic or non-aromatic, and can further comprise heteroatoms, for example, halogens, oxygen, nitrogen, sulfur, silicon, or phosphorous. The Ci_i8 organic bridging group can be disposed such that the C₆ arylene groups connected thereto are each connected to a common alkylidene carbon or to different carbons of the CM_S organic bridging group, p and q can each be 1, and R^a and R^b are each a C_1-3 alkyl group, specifically, methyl, disposed meta to the hydroxy group on each arylene group.

[0019] X^a can be a substituted or unsubstituted C₃_i₈ cycloalkylidene, a Ci_₂5 alkylidene of formula -C(R^c)(R^d)- wherein R^c and R^d are each independently hydrogen, C_1-12 alkyl, C_1-12 cycloalkyl, C_7-12 arylalkyl, C_1-12 heteroalkyl, or cyclic C_7-12 heteroarylalkyl, or a group of the formula -C(=R⁶)- wherein R^e is a divalent C_1-12 hydrocarbon group. Groups of this type include methylene, cyclohexylmethylene, ethylidene, neopentylidene, and isopropylidene, as well as 2-[2.2.1]-bicycloheptylidene, cyclohexylidene, cyclopentylidene, cyclododecylidene, and adamantylidene.

[0020] X^a can be a C_1-18 alkylene group, a C₃_i₈ cycloalkylene group, a fused C₆-i₈ cycloalkylene group, or a group of the formula -B 1 -G-B2 - wherein B 1 and B2 are the same or different C_1-6 alkylene group and G is a C_3-12 cycloalkylidene group or a C₆-i6 arylene group. For example, X^a can be a substituted C_3-18 cycloalkylidene of formula (4)

wherein R^r, R^p, R^q, and R^£ are each independently hydrogen, halogen, oxygen, or C_1-12 hydrocarbon groups; Q is a direct bond, a carbon, or a divalent oxygen, sulfur, or -N(Z)- where Z is hydrogen, halogen, hydroxy, C_1-12 alkyl, C_1-12 alkoxy, or C_1-12 acyl; r is 0 to 2, t is 1 or 2, q is 0 or 1, and k is 0 to 3, with the proviso that at least two of R^r, R^p, R^q, and R^£ taken together are a fused cycloaliphatic, aromatic, or heteroaromatic ring. It will be understood that where the fused ring is aromatic, the ring as shown in formula (4) will have an unsaturated carbon-carbon linkage where the ring is fused. When k is one and q is 0, the ring as shown in formula (4) contains 4 carbon atoms, when k is 2, the ring as shown in formula (4) contains 5 carbon atoms, and when k is 3, the ring contains 6 carbon atoms. Two adjacent groups (e.g., R^q and R^£ taken together) can form an aromatic group or R^q and R^£ taken together can form one aromatic group and R^r and R^p taken together can form a second aromatic group. When R^q and R^£ taken together form an aromatic group, R^p can be a double- bonded oxygen atom, i.e., a ketone.

[0021] Specific examples of bisphenol compounds of formula (3) include l,l-bis(4- hydroxyphenyl) methane, l,l-bis(4-hydroxyphenyl) ethane, 2,2-bis(4-hydroxyphenyl) propane (also referred to as "bisphenol A" or "BPA"), 2,2-bis(4-hydroxyphenyl) butane, 2,2- bis(4-hydroxyphenyl) octane, l,l-bis(4-hydroxyphenyl) propane, l,l-bis(4-hydroxyphenyl) n-butane, 2,2-bis(4-hydroxy-2-methylphenyl) propane, l,l-bis(4-hydroxy-t-butylphenyl) propane, 3,3-bis(4-hydroxyphenyl) phthalimidine, 2-phenyl-3,3-bis(4-hydroxyphenyl) phthalimidine (PPPBP), or l,l-bis(4-hydroxy-3-methylphenyl)cyclohexane (DMBPC).

Combinations comprising at least one of the foregoing bisphenols can also be used. The bisphenol can comprise bisphenol A, in which each of A 1 and A2 can be p-phenylene, and Y 1 can be isopropylidene in formula (3).

[0022] A catalyst can be used to facilitate the polycarbonate polymerization. The catalyst can comprise one or both of a quaternary catalyst or an alkali catalyst. The quaternary catalyst comprises at least one of a quaternary ammonium compound or a quaternary phosphonium compound. The quaternary ammonium compound can be a compound of the structure (R⁴)₄N⁺X^~, wherein each R⁴ is the same or different, and is a C_1-2o alkyl, a C₄_₂o cycloalkyl, or a C₄_₂o aryl; and X^" is an organic or inorganic anion, for example, a hydroxide, halide, carboxylate, sulfonate, sulfate, formate, carbonate, or bicarbonate. Examples of organic quaternary ammonium compounds include tetramethyl ammonium hydroxide, tetrabutyl ammonium hydroxide, tetramethyl ammonium acetate, tetramethyl ammonium formate, or tetrabutyl ammonium acetate.

[0023] The quaternary phosphonium compound can be a compound of the structure (R⁵)₄P⁺X^~, wherein each R⁵ is the same or different, and is a C_1-2o alkyl, a C₄-₂o cycloalkyl, or a C₄_₂o aryl; and X^" is an organic or inorganic anion, for example, a hydroxide, phenoxide, halide, carboxylate, for example, acetate or formate, sulfonate, sulfate, formate, carbonate, or bicarbonate. Where X^" is a polyvalent anion, for example, carbonate or sulfate, it is understood that the positive and negative charges in the quaternary ammonium and phosphonium structures are properly balanced. For example, where each R⁵ is methyl and

X^" is carbonate, it is understood that X -^" represents 2(C0₃ -^~2 ).

[0024] Examples of organic quaternary phosphonium compounds include tetramethyl phosphonium hydroxide, tetramethyl phosphonium acetate, tetramethyl phosphonium formate, tetrabutyl phosphonium hydroxide, tetraethyl phosphonium acetate, tetrapropyl phosphonium acetate, tetrabutyl phosphonium acetate (TBPA) , tetrapentyl phosphonium acetate, tetrahexyl phosphonium acetate, tetraheptyl phosphonium acetate, tetraoctyl phosphonium acetate, tetradecyl phosphonium acetate, tetradodecyl phosphonium acetate, tetratolyl phosphonium acetate, tetramethyl phosphonium benzoate, tetraethyl phosphonium benzoate, tetrapropyl phosphonium benzoate, tetraphenyl phosphonium benzoate, tetraethyl phosphonium formate, tetrapropyl phosphonium formate, tetraphenyl phosphonium formate, tetramethyl phosphonium propionate, tetraethyl phosphonium propionate, tetrapropyl phosphonium propionate, tetramethyl phosphonium butyrate, tetraethyl phosphonium butyrate, tetrapropyl phosphonium butyrate, tetraphenyl phosphonium acetate (TPPA), or tetraphenyl phosphonium phenoxide (TPPP). The quaternary catalyst can comprise at least one of tetrabutyl phosphonium acetate, TPPP, or TPPA.

[0025] The amount of the quaternary catalyst can be added based upon the total number of moles of bisphenol employed in the polymerization reaction. When referring to the ratio of catalyst, for example, phosphonium salt, to all bisphenols employed in the polymerization reaction, it is convenient to refer to moles of phosphonium salt per mole of the bisphenol(s), meaning the number of moles of phosphonium salt divided by the sum of the moles of each individual bisphenol present in the reaction mixture. The amount of the optional quaternary catalyst (e.g., organic ammonium or phosphonium salts) can each independently be employed in an amount of 1 x 10^"2 to 1 x 10^"5, or 1 x 10^"3 to 1 x 10^"4 moles per total mole of the bisphenol(s) in the monomer mixture.

[0026] The alkali catalyst comprises a source of one or both of alkali ions or alkaline earth ions. The sources of these ions can include alkaline earth hydroxides, for example, magnesium hydroxide or calcium hydroxide. Sources of alkali metal ions can include the alkali metal hydroxides, for example, at least one of lithium hydroxide, sodium hydroxide, or potassium hydroxide. Examples of alkaline earth metal hydroxides are calcium hydroxide or magnesium hydroxide. The alkali catalyst can comprise sodium hydroxide. Other possible sources of alkaline earth or alkali metal ions include salts of carboxylic acids (for example, sodium acetate) or derivatives of ethylene diamine tetraacetic acid (EDTA) (for example, EDTA tetrasodium salt, or EDTA magnesium disodium salt). For example, the alkali catalyst can comprise at least one of an alkali metal salt(s) of a carboxylic acid or an alkaline earth metal salt(s) of a carboxylic acid. In another example, the alkali catalyst comprises Na₂Mg EDTA or a salt thereof.

[0027] The alkali catalyst can also, or alternatively, comprise salt(s) of a non- volatile inorganic acid. For example, the alkali catalyst can comprise at least one of NaH₂P0₃, NaH₂P0₄, Na₂HP0₃, KH₂P0₄, CsH₂P0₄, or Cs₂HP0₄. Alternatively, or in addition, the alkali catalyst can comprise mixed alkali metal salt(s) of phosphoric acid, for example, at least one of NaKHP0₄, CsNaHP0₄, or CsKHP0₄. The alkali catalyst can comprise

KNaHP0₄, wherein a molar ratio of Na to K is 0.5 to 2.

[0028] The alkali catalyst typically can be used in an amount sufficient to provide 1 x

10 -^"2 to 1 x 10 -^"8 moles, or 1 x 10 -^"4 to 1 x 10 -^"7 moles of metal hydroxide per mole of the bisphenol(s).

[0029] Quenching of the transesterification catalysts and any reactive catalysts residues with an acidic compound after polymerization can be completed and can be useful in some melt polymerization processes. Among the many quenchers that can be used are alkyl

8 9 8

sulfonic esters of the formula R S0₃R wherein R is hydrogen, C_1-12 alkyl, C₆-i8 aryl, or C₇_i9 alkylaryl, and R⁹ is C_1-12 alkyl, C_6-18 aryl, or C₇_i9 alkylaryl. Examples of quenchers include benzenesulfonate, p-toluenesulfonate, methylbenzene sulfonate, ethylbenzene sulfonate, n- butyl benzenesulfonate, octyl benzenesulfonate, phenyl benzenesulfonate, methyl p- toluenesulfonate, ethyl p-toluenesulfonate, n-butyl p-toluene sulfonate, octyl p- toluenesulfonate, or phenyl p-toluenesulfonate. In particular, the quencher can comprise an alkyl tosylate, for example, n-butyl tosylate. [0030] In the melt polymerization method, the polycarbonate can be prepared by reacting, in a molten state, the carbonate compound and the dihydroxy compound in the presence of the catalyst. The reaction can be carried out in typical polymerization equipment, such as at least one of a continuously stirred reactor (CSTR), plug flow reactor, wire wetting fall polymerizers, free fall polymerizers, horizontal polymerizers, wiped film polymerizers, BANBURY mixers, or single or twin screw extruders. Volatile by-products, such as phenol, are removed from the molten reactants by distillation and the polymer is isolated as a molten residue. Melt polymerization can be conducted as a batch process or as a continuous process. In either case, the melt polymerization conditions used can comprise two or more distinct reaction stages.

[0031] For example, the polymerization can comprise an oligomerization stage in which the starting dihydroxy compound and the carbonate compound such as a diaryl carbonate are converted into an oligomeric polycarbonate and a second reaction stage also referred to as a polymerization stage wherein the oligomeric polycarbonate formed in the oligomerization stage is converted to high molecular weight polycarbonate. The

oligomerization stage can comprise 1 or more, or 2 or more, or 2 to 4 oligomerization units (for example, 2 to 4 continuously stirred tanks). When 2 or more oligomerization units are present in series, one or both of an increase in temperature and a decrease in pressure can occur from one unit to the next.

[0032] The oligomerization stage can comprise a first oligomerization unit located in series and upstream of a second oligomerization unit. The temperature in a first

oligomerization unit can be 160 to 300 degrees Celsius (°C), or 160 to 275°C, or 160 to 250°C, or 200 to 270°C, or 230 to 270°C. The pressure in a first oligomerization unit can be 50 to 200 millibar absolute (mbar), or 75 to 200 mbar. The viscosity of the stream exiting the first oligomerization unit can be 0.05 to 1 Pascal seconds (Pa^'s), or 0.05 to 0.5 Pa s. The temperature in a second oligomerization unit can be 250 to 300°C, or 270 to 300°C. The pressure in a second oligomerization unit can be 5 to 50 mbar, or 10 to 40 mbar. The viscosity of the stream exiting the second oligomerization unit can be 0.5 to 10 Pa s, or 1 to 5 Pa s, or greater than or equal to 1 Pa s.

[0033] The polymerization stage can comprise 1 or more, or 2 or more, or 2 polymerization units (for example, wire wetting fall polymerization units, horizontal polymerizers, vertical polymerizers, reactive extruders, or a continuously stirred tanks) located downstream of the oligomerization units. The polymerization stage can occur at a temperature of 240 to 350°C, or 280 to 300°C, or 240 to 270°C, or 250 to 310°C. The polymerization can occur in a series of polymerization units that can each individually have increasing temperature and/or vacuum. The polymerization stage can comprise a first polymerization unit located in series and upstream of a second polymerization unit. The first polymerization unit can be at a temperature of 240 to 350°C, or 260 to 310°C and a pressure of 100 to 1,100 mbar, or 250 to 900 mbar. The second polymerization unit can be at a temperature of 240 to 350°C, or 260 to 300°C and a pressure of less than or equal to 600 mbar, or 100 to 500 mbar.

[0034] A chain scission agent can be added to a stream downstream of a final polymerization unit (e.g. a polymerization unit) in order to modify the resultant molecular weight of the polycarbonate without changing the processing conditions and upstream of an extruder. Addition of the chain scission agent has the benefit of being able to easily modify the molecular weight of the polycarbonate produced without changing the processing parameters. The present method of monitoring and adjusting the flowrate of the chain scission agent can be particularly helpful in maintaining a target viscosity during

polymerization and can also be helpful during a changeover process such that the production of large amounts of waste or off-spec polymer can be avoided. The polycarbonate can be split into multiple streams and each stream independently can be adjusted or not adjusted, depending upon a target molecular weight of the melt polycarbonate of the respective stream.

[0035] The chain scission agent can be added in an amount of 1 to 70 wt%, or 1 to 25 wt%, or 1 to 5 wt% based on the total weight of the chain scission stream and the

polycarbonate stream.

[0036] The chain scission agent can be added after a final polymerization (e.g., after a final polymerization unit). As used herein, "after final polymerization" refers to a time after which the weight average molecular weight (Mw) does not increase by greater than 10 weight percent (wt%). Preferably, the Mw does not increase by greater than or equal to 5 wt% after final polymerization. If there is a devolatization after final polymerization, then the chain scission agent can be added upstream of and/or directly to and/or downstream of the devolatization. The chain scission agent can be added after the final polymerization and before the polycarbonate enters an extruder. For example, a conduit (for example, a pipe) can connect a final polymerization unit and an extruder and the chain scission agent can be added to the conduit. A mixing element such as a static mixer can be present along the distance of the conduit to allow for mixing of the chain scission agent and the polycarbonate thus forming the adjusted stream downstream of the mixing element.

[0037] The chain scission agent can be added upstream of a quencher. It is noted that as used herein, when a first component is added "upstream" of a second component, it is understood that the first component can be added in a location upstream of the addition location of the second component or, where applicable, the first component can be added in the same location, but at a time prior to the addition of the second component. For example, a chain scission agent can be added to a devolatization unit, the polycarbonate can be mixed for an amount of time, and subsequently, a quencher can be added. If a quencher is added upstream of the chain scission agent, then, in addition to the chain scission agent, a catalyst is added, wherein a second quencher can be added downstream of the chain scission agent and catalyst.

[0038] The chain scission agent can be any agent that breaks the polycarbonate chain, for example, at least one of a carbonate source, water, or an aryl alcohol. The chain scission agent can comprise at least one of a diaryl carbonate (such as diphenyl carbonate, di-p-tert- butyl phenol carbonate, di-paracumyl phenol carbonate, di-dicumyl phenol carbonate, bismethyl salicyl carbonate, or di-p-hydroxy benzonitrile carbonate), p-hydroxy benzonitrile, paracumyl phenol, p-tert-butyl phenol, dicumyl phenol, methyl phenyl carbonate, dimethyl carbonate, diethyl carbonate, ethyl phenyl carbonate, phenol, a dihydroxy compound (for example, BPA), or water. The chain scission agent can comprise a diaryl carbonate with an electron withdrawing group such as at least one of bis(4-nitrophenyl)carbonate, bis(2- chlorophenyl)carbonate, bis(4-chlorophenyl) carbonate, bis(methyl salicyl)carbonate, bis(4- methylcarboxylphenyl) carbonate, bis(2-acetylphenyl) carboxylate, or bis(4-acetylphenyl) carboxylate. The chain scission agent can comprise a combination comprising at least one of the foregoing chain scission agents.

[0039] Specifically, the chain scission agent can comprise a chain scission agent that will not cause a reduction in the endcap level of the resulting polycarbonate, for example, chain scission agent can comprise a diaryl carbonate. The chain scission agent can comprise or can consist of diphenyl carbonate (DPC). The chain scission agent can comprise at least one of a monomer used in the polymerization process, water, or an amount of a

polymerization by-product. For example, if the polymerization occurring in the

polymerization unit is the polymerization of a bisphenol A homopolycarbonate, then the polymerization can occur by the following scheme: DPC + BP A PC + PhOH

In this scheme, diphenyl carbonate (DPC) reacts with bisphenol A (BPA) to form the polycarbonate (PC) and phenol (PhOH) as a by-product. Adding one or more of phenol, DPC, or water will act to break the polymer chain to result in a decrease in the molecular weight of the polycarbonate.

[0040] The chain scission agent can be added as a molten agent (for example, consisting of the pure molten agent) or can be dissolved in a solvent (for example, at least one of anisole, toluene, or acetone) that is inert to the polymerization.

[0041] The amount of chain scission agent to be added is based upon the molecular weight of the polycarbonate (e.g., the initial molecular weight), and the target molecular weight (e.g., final molecular weight). The amount of chain scission agent can be an amount that will reduce the molecular weight of the polymerized polycarbonate to a modified or final molecular weight. The specific amounts can readily be determined using the feedforward or the feedback loop.

[0042] A feedforward or a feedback loop can be employed to monitor and adjust the addition rate of the chain scission agent. Specifically, a method of adding a chain scission agent to a melt polycarbonate polymerization can comprise polymerizing a feed stream in a final polymerization unit to form a polycarbonate stream comprising a polycarbonate;

controlling a scission stream flowrate of a chain scission stream comprising the chain scission agent; and mixing the chain scission stream and the polycarbonate stream to form an adjusted stream comprising a reduced molecular weight polycarbonate. The controlling the scission stream flowrate of a chain scission stream can comprise determining an upstream viscosity, an upstream temperature, and optionally an upstream flowrate of the polycarbonate stream and controlling the scission stream flowrate based on the upstream viscosity, the upstream temperature, and optionally on the upstream flow rate. The controlling the scission stream flowrate of a chain scission stream can comprise determining a downstream viscosity and a downstream temperature of the adjusted stream and controlling the scission stream flowrate based on the downstream viscosity and the downstream temperature. In all cases, the flowrate of the chain scission agent can be adjusted based on the real-time process to achieve a more consistent polycarbonate.

[0043] The upstream temperature and the downstream temperature can each independently be 250 to 350°C. The endcap level of the polycarbonate stream can be 50 to 98%. [0044] A feedforward loop can be used to control the flowrate of the chain scission agent. For example, the upstream viscosity, the upstream temperature, the upstream flow rate, and the endcap level of the polycarbonate stream can be measured. As is described above, the upstream properties refer to the properties of the stream before a feed location of the chain scission agent, and the flowrate of the chain scission agent can be adjusted based on the difference between the upstream viscosity and a target viscosity value.

[0045] The feedforward loop relies on an assumed correlation between the adjustment amount of chain scission agent and the target molecular weight. It was surprisingly discovered that this correlation is not universal and that the endcapping level of the polycarbonate affects the amount of chain scission agent needed to obtain the target molecular weight. Therefore, as the system deviates from the correlation function, the endcap level of the polycarbonate stream should be determined and the correlation function adjusted.

[0046] FIG. 1 is an illustration of a method of controlling the scission stream flowrate of a chain scission stream using a feedforward loop. In FIG. 1, feed stream 8 is added to final polymerization unit 10 to produce polycarbonate stream 12 comprising a polycarbonate. The upstream viscosity is measured using polycarbonate stream viscometer 40 and the upstream temperature is measured using polycarbonate stream thermocouple 50. The upstream flow rate is measured based on pump 30 using flowrate controller 32. The upstream viscosity and the upstream temperature of polycarbonate stream 12 are transmitted via polycarbonate stream viscosity signal 44 to chain scission agent flowrate controller 70. The upstream flowrate of polycarbonate stream 12 is transmitted via flowrate signal 34 to chain scission agent flowrate controller 70. The endcap level of polycarbonate stream 12 is determined experimentally and the value entered into chain scission agent flowrate controller 70. Based on these values and a target viscosity, chain scission agent flowrate controller 70 adjusts a flowrate of chain scission stream 62 from chain scission agent tank 60, for example, by adjusting a valve position. Chain scission stream 62 is added to polycarbonate stream 12 and the combined stream is mixed in static mixer 16 to form adjusted stream 18.

[0047] A feedback loop can be used to control the flowrate of the chain scission agent. For example, the downstream viscosity of the adjusted stream, the downstream temperature of the adjusted stream, and the upstream flow rate of the polycarbonate stream can be measured. As is described above, the upstream properties refer to the properties of the stream before a feed location of the chain scission agent and the downstream properties refer to the properties of the adjusted stream after mixing of the chain scission agent stream the polycarbonate stream. The downstream viscosity at the downstream temperature can then be compared to a target viscosity value at that temperature and an adjustment amount of the flowrate of the chain scission agent can be determined using a correlation function based on this difference and the upstream flow rate of the polycarbonate stream. This method advantageously does not rely on determination of the endcap level.

[0048] FIG. 2 is an illustration of a method of controlling the scission stream flowrate of a chain scission stream using a feedback loop. In FIG. 2, feed stream 8 is added to final polymerization unit 10 to produce polycarbonate stream 12 comprising a polycarbonate. The downstream viscosity is measured using adjusted stream viscometer 140 and the downstream temperature is measured using adjusted stream thermocouple 150. The upstream flow rate is measured based on pump 30 using flowrate controller 32. The downstream viscosity and the downstream temperature of adjusted stream 18 are transmitted via adjusted stream viscosity signal 144 to chain scission agent flowrate controller 70. The upstream flowrate of polycarbonate stream 12 is transmitted via flowrate signal 34 to chain scission agent flowrate controller 70. Based on these values and a target viscosity, chain scission agent flowrate controller 70 adjusts a flowrate of chain scission stream 62 from chain scission agent tank 60, for example, by adjusting a valve position.

[0049] A differential feedback loop can be used to control the flowrate of the chain scission agent. For example, the upstream viscosity of polycarbonate stream, the upstream temperature of polycarbonate stream, the downstream viscosity of the adjusted stream, and the downstream temperature of the adjusted stream can be measured. A differential viscosity can be determined based on the upstream viscosity at the upstream temperature compared to the downstream viscosity at the downstream temperature. The downstream viscosity at the downstream temperature can be compared to a target viscosity value at that temperature and an adjustment amount of the flowrate of the chain scission agent can be determined using a correlation function based on the differential viscosity and the upstream flow rate of the polycarbonate stream. This method advantageously does not rely on determination of the endcap level and as both the upstream viscosity and the downstream viscosity are determined, more precise control of the resultant molecular weight can be achieved.

[0050] FIG. 3 is an illustration of a method of controlling the scission stream flowrate of a chain scission stream using a differential feedback loop. In FIG. 3, feed stream 8 is added to final polymerization unit 10 to produce polycarbonate stream 12 comprising a polycarbonate. The upstream viscosity is measured using polycarbonate stream viscometer 40 and the upstream temperature is measured using polycarbonate stream thermocouple 50. The upstream viscosity and the upstream temperature of polycarbonate stream 12 are transmitted via polycarbonate stream viscosity signal 44 to differential unit 100. The downstream viscosity is measured using adjusted stream viscometer 140 and the downstream temperature is measured using adjusted stream thermocouple 150. The downstream viscosity and the downstream temperature of adjusted stream 18 are transmitted via adjusted stream viscosity signal 144 to differential unit 100. The differential viscosity is transmitted to chain scission agent flowrate controller 70 via differential viscosity signal 102. The upstream flowrate of polycarbonate stream 12 is transmitted via flowrate signal 34 to chain scission agent flowrate controller 70. Based on these values and a target viscosity, chain scission agent flowrate controller 70 adjusts a flowrate of chain scission stream 62 from chain scission agent tank 60, for example, by adjusting a valve position.

[0051] While flowrate controller 32 is illustrated in the figures as determining the flowrate based on a pump 30, it is understood that the flowrate on the stream can be determined using a flowmeter. Likewise, while the mixing is illustrated to occur in static mix 16 in the figures, mixing can likewise occur by other means such as in a continuously stirred tank or merely be combining the streams, for example, using a T-junction.

[0052] The method can further comprise adjusting a pressure in the final

polymerization unit based on the upstream temperature and the upstream viscosity as adjusting the pressure in the final polymerization controls the amount of by-product removed from the polymerization, which has a direct effect on the viscosity of the polycarbonate stream. An illustration of adjusting the pressure in the final polymerization unit is illustrated in FIG. 1, FIG. 2, and FIG. 3 that illustrate that the upstream viscosity and the upstream temperature can be transmitted to pressure controller 80 via polycarbonate stream pressure control signal 42.

[0053] Similar to adjusting the pressure in the final polymerization unit, the method can likewise control adjusting the pressure in a leading polymerization unit. An illustration of adjusting the pressure in a leading polymerization unit (e.g., and upstream polymerization unit) that is located upstream of the final polymerization unit is illustrated in FIG. 4 that illustrates that the viscosity and temperature of feed stream 8 can be determined using feed stream viscometer 240 and feed stream thermocouple 250, respectively. These values can then be transmitted to polymerizer pressure controller 280 via feed stream pressure control signal 242.

[0054] The present method of adding a chain scission agent can result in one or both of a measured weight average molecular weight of the reduced molecular weight

polycarbonate in the adjusted stream at any given time during the polymerization being within 5%, or within 1% of an average weight average molecular weight of the reduced molecular weight polycarbonate; and a weight average molecular weight based on polycarbonate standards of the reduced molecular weight polycarbonate varying by plus or minus 500 Daltons, or by plus or minus 300 Daltons.

[0055] A weight average molecular weight based on polycarbonate standards of the polycarbonate in the polycarbonate stream can be greater than or equal to 35,000 Daltons, or greater than or equal to 56,000 Daltons, or 35,000 to 100,000 Daltons, or 30,000 to 100,000 Daltons and a weight average molecular weight based on polycarbonate standards of the reduced molecular weight polycarbonate in the adjusted stream can be 30,000 to 100,000 Daltons, or less than or equal to 80,000 Daltons, or less than or equal 45,000 Daltons, or 8,000 to 80,000 Daltons; provided that the reduced molecular weight of the polycarbonate in the adjusted stream is less than the molecular weight of the polycarbonate in the

polycarbonate stream.

[0056] The polycarbonate can have a melt volume flow rate (MVR) of less than or equal to 7 cubic centimeters per 10 minutes (cm 3 /10 min), or 3 to 7 cm 3 /10 min measured at 300°C under a load of 1.2 kilograms (kg) according to ASTM D1238-04 prior to the addition of the chain scission agent. The MVR of the polycarbonate in the adjusted stream can be less than or equal to 7 cm 3 /10 min, or 3 to 7 cm 3 /10 min measured at 300°C under a load of 1.2 kg according to ASTM D1238-04. The MVR of the polycarbonate in the adjusted stream can be greater than or equal to 7 cm 3 /10 min, or 7 to 20 cm 3 /10 min, or 8 to 10 cm 3 /10 min measured at 300°C under a load of 1.2 kg according to ASTM D1238-04

[0057] The present process can be especially beneficial in a large production facility with a production rate of greater than or equal to 65,000 tons per year (tons/yr), or greater than or equal to 100,000 tons/yr. For example, in a large production facility with a production rate of 65,000 tons/yr, a standard changeover time to change product MVR from 6 to 65 cm /10 min of 4.5 hours would result in 50 tons of waste and/or off-spec polycarbonate per transition. Reducing the changeover time to 0.5 hour reduces the amount of waste and/or off-spec polycarbonate generated by a factor of ten to only 5 tons of waste polycarbonate per transition and further reducing the changeover time to 0.2 hour reduces the amount of waste generated to only 1.7 tons of waste polycarbonate per transition. Hence, significant savings and improvements can be realized with the present process, which is especially evident in large scale melt polycarbonate production plants, e.g., greater than 55,000 tons/yr, or greater than or equal to 100,000 tons/yr, or greater than or equal to 200,000 tons/yr (91 Mg/day), or greater than or equal to 300,000 tons/yr.

[0058] An additive can be added to the polycarbonate, for example, in an extruder located downstream of the polymerization stage. The additive can comprise, for example, at least one of an impact modifier, a flow modifier, a filler (e.g., a particulate

polytetrafluoroethylene (PTFE), glass, carbon, a mineral, or metal), a reinforcing agent (e.g., glass fibers), an antioxidant, a heat stabilizer, a light stabilizer, an ultraviolet (UV) agent (such as a UV light stabilizer or a UV absorbing additive), a plasticizer, a lubricant, a release agent (such as a mold release agent (such as glycerol monostearate, pentaerythritol stearate, glycerol tristearate, or stearyl stearate)), an antistatic agent, an antifog agent, an antimicrobial agent, a colorant (e.g., a dye or pigment), a surface effect additive, a radiation stabilizer, a flame retardant, or an anti-drip agent (e.g., a PTFE-encapsulated styrene-acrylonitrile copolymer (TSAN)). For example, a combination of a heat stabilizer, mold release agent, and/or ultraviolet light stabilizer can be used. In general, the additives are used in the amounts generally known to be effective. For example, the total amount of the additive composition (other than any impact modifier, filler, or reinforcing agent) can be 0.001 to 10.0 wt%, or 0.01 to 5 wt%, each based on the total weight of the polymer in the polymerized composition.

[0059] The following examples are provided to illustrate the present method. The examples are merely illustrative and are not intended to limit devices made in accordance with the disclosure to the materials, conditions, or process parameters set forth therein.

EXAMPLES

Examples 1-3: Response time after a viscosity disruption

[0060] Melt polycarbonate polymerizations having a viscosity disruption occurring at time -5 to 0 minutes were modelled in Examples 1-3. In Example 1, the viscosity of the polycarbonate was determined based on a laboratory measurement and the pressure in the final polymerization unit adjusted based on the measured viscosity. In Example 2, a mathematical function was used to estimate the final molecular weight based on the process parameters and the pressure in the final polymerization unit adjusted based on the estimated viscosity. In Example 3, a feedback control loop in accordance with FIG. 2 was used to adjust the flowrate of the chain scission agent. The results are illustrated in FIG. 5.

[0061] FIG. 5 illustrates that Example 1 resulted in the longest response time of more than 75 minutes to realize the change with an additional 50 minutes response time (125 minutes total) for the pressure change in the final polymerization unit to return the polycarbonate back to the target viscosity. This long response time is due to the time required to experimentally determine the viscosity of the polycarbonate. Example 2 also had a long response time of more than 20 minutes to realize the change with an additional 50 minutes response time (70 minutes total) for the pressure change in the final polymerization unit to return the polycarbonate back to the target viscosity. Example 3 illustrates a significantly improved response time of only 5 minutes for the system to both acknowledge and response to the change in viscosity of the polycarbonate and to return the polycarbonate back to the target viscosity.

[0062] Set forth below are non-limiting aspects of the present disclosure.

[0063] Aspect 1: A method for the manufacture of a melt polycarbonate, comprising: melt polymerizing a feed stream in a final polymerization unit to form a polycarbonate stream comprising a polycarbonate; controlling a scission stream flowrate of a chain scission stream comprising the chain scission agent; and mixing the chain scission stream and the

polycarbonate stream to form an adjusted stream comprising a reduced molecular weight polycarbonate. The controlling can comprise one or both of determining an upstream viscosity, an upstream temperature, and optionally one or both of an upstream flowrate and an endcap level of the polycarbonate stream and controlling the scission stream flowrate based on the upstream viscosity, the upstream temperature, and optionally on one or both of the upstream flow rate and the endcap level; and determining a downstream viscosity and a downstream temperature of the adjusted stream and controlling the scission stream flowrate based on the downstream viscosity and the downstream temperature. The controlling can comprise determining an upstream viscosity, an upstream temperature, an upstream flowrate, and an endcap level of the polycarbonate stream and controlling the scission stream flowrate based on the upstream viscosity, the upstream temperature, the upstream flow rate, and the endcap level. The controlling can comprise determining the upstream flow rate of the polycarbonate stream, determining a downstream viscosity and a downstream temperature of the adjusted stream, and controlling the scission stream flowrate based on the upstream flow rate, the downstream viscosity and the downstream temperature. The controlling can comprise determining the upstream viscosity and the upstream temperature of the

polycarbonate stream, determining the downstream viscosity and the downstream

temperature of the adjusted stream, and controlling the scission stream flowrate based on the upstream viscosity, the upstream temperature, downstream viscosity, and the downstream temperature.

[0064] Aspect 1.1: A method for the manufacture of a melt polycarbonate, comprising: melt polymerizing a feed stream in a final polymerization unit to form a polycarbonate stream comprising a polycarbonate for an amount of time; after the amount of time, initiating a scission stream flowrate of a chain scission stream comprising the chain scission agent; controlling the scission stream flowrate; and mixing the chain scission stream and the polycarbonate stream to form an adjusted stream comprising a reduced molecular weight polycarbonate; wherein a changeover time from the melt polymerizing the

polycarbonate and the mixing to form the reduced molecular weight polycarbonate is less than or equal to 1 hour, or less than or equal to 0.5 hours, or 0.1 to 1 hour, or 0.05 to 0.2 hours. The controlling comprises one or both of determining an upstream viscosity, an upstream temperature, and optionally one or both of an upstream flowrate and an endcap level of the polycarbonate stream and controlling the scission stream flowrate based on the upstream viscosity, the upstream temperature, and optionally on one or both of the upstream flow rate and the endcap level; and determining a downstream viscosity and a downstream temperature of the adjusted stream and controlling the scission stream flowrate based on the downstream viscosity and the downstream temperature.

[0065] Aspect 2: The method of Aspect 1 or 1.1, wherein the controlling comprises determining the upstream viscosity, the upstream temperature, the upstream flow rate, and the endcap level of the polycarbonate stream.

[0066] Aspect 3: The method of Aspect 2, wherein the controlling comprises transmitting an upstream viscosity signal based on the upstream viscosity and the upstream temperature; transmitting an upstream flowrate signal of the polycarbonate stream based on the upstream flowrate; determining an adjustment scission stream flowrate based on the upstream viscosity signal and the upstream flowrate signal; and adjusting the scission stream flowrate to the adjustment scission stream flowrate. [0067] Aspect 4: The method of Aspect 1 or 1.1, wherein the controlling comprises determining the downstream viscosity and the downstream temperature of the adjusted stream.

[0068] Aspect 5: The method of Aspect 4, wherein the controlling comprises transmitting a downstream viscosity signal based on the downstream viscosity and the downstream temperature; determining an adjustment scission stream flowrate based on the downstream viscosity signal; and adjusting the scission stream flowrate to the adjustment scission stream flowrate.

[0069] Aspect 6: The method of Aspect 1 or 1.1, wherein the controlling comprises determining the upstream viscosity and the upstream temperature of the polycarbonate stream and determining the downstream viscosity and the downstream temperature of the adjusted stream.

[0070] Aspect 7: The method of Aspect 6, wherein the controlling comprises transmitting an upstream viscosity signal based on the upstream viscosity and the upstream temperature; transmitting a downstream viscosity signal based on the downstream viscosity and the downstream temperature; determining a differential between the upstream viscosity signal and the downstream viscosity signal; and adjusting the scission stream flowrate to an adjustment scission stream flowrate.

[0071] Aspect 8: The method of any one or more of Aspects 1, 1.1, and 4 to 7, further comprising determining the upstream flowrate of the polycarbonate stream.

[0072] Aspect 9: The method of any one or more of the preceding aspects, further comprising determining an endcap level of the polycarbonate stream and adjusting the scission stream flowrate based on the upstream viscosity and the endcap level.

[0073] Aspect 10: The method of any one or more of the preceding aspects, further comprising transmitting a polycarbonate stream pressure control signal based on the upstream viscosity to a pressure controller and adjusting a pressure in the final polymerization unit based on the polycarbonate stream pressure control signal.

[0074] Aspect 11: The method of any one or more of the preceding aspects, further comprising polymerizing the polycarbonate in a leading polymerization unit located upstream of the final polymerization unit to form the feed stream; and transmitting a feed stream pressure control signal from a feed stream viscometer to a polymerizer pressure controller and adjusting a pressure in a leading polymerization unit based on the feed stream pressure control signal. [0075] Aspect 12: The method of any one or more of the preceding aspects, wherein a measured weight average molecular weight of the reduced molecular weight polycarbonate in the adjusted stream at any given time during the polymerization is within 5% of an average weight average molecular weight of the reduced molecular weight polycarbonate; and/or wherein a weight average molecular weight based on polycarbonate standards of the reduced molecular weight polycarbonate varies by plus or minus 500 Daltons.

[0076] Aspect 13: The method of any one or more of the preceding aspects, wherein a weight average molecular weight based on polycarbonate standards of the polycarbonate in the polycarbonate stream is greater than or equal to 35,000 Daltons and a weight average molecular weight based on polycarbonate standards of the reduced molecular weight polycarbonate in the adjusted stream is less than or equal to 80,000 Daltons; wherein the reduced molecular weight of the polycarbonate in the adjusted stream is less than the molecular weight of the polycarbonate in the polycarbonate stream.

[0077] Aspect 14: The method of any one or more of the preceding aspects, wherein the chain scission agent comprises at least one of a carbonate source, water, or an aryl alcohol, preferably, wherein the chain scission agent comprises at least one of a diphenyl carbonate, methyl phenyl carbonate, dimethyl carbonate, diethyl carbonate, ethyl phenyl carbonate, or phenol.

[0078] Aspect 15: The method of any one or more of the preceding aspects, wherein the polycarbonate comprises a bisphenol A polycarbonate and the chain scission agent comprises diphenyl carbonate.

[0079] Aspect 16: The method of any one or more of the preceding aspects, wherein the melt polymerizing comprises melt polymerizing for an amount of time prior to the controlling and the mixing; and wherein the method further comprises initiating the scission stream flowrate.

[0080] Aspect 17: The method of Aspect 16, wherein a changeover time from the melt polymerizing the polycarbonate and the mixing to form the reduced molecular weight polycarbonate is less than or equal to 1 hour, or less than or equal to 0.5 hours, or 0.1 to 1 hour, or 0.05 to 0.2 hours.

[0081] Aspect 18: The method of any one or more of the preceding aspects, wherein the melt polymerizing produces the polycarbonate at a rate of 15,000 to 150,000 tons/year, or greater than 55,000 tons/yr, or greater than or equal to 65,000 tons/yr, or greater than or equal to 100,000 tons/yr, or greater than or equal to 200,000 tons/yr, or greater than or equal to 300,000 tons/yr.

[0082] Aspect 19: The method of any one or more of the preceding aspects, wherein a weight average molecular weight based on polycarbonate standards of the polycarbonate in the polycarbonate stream is greater than or equal to 35,000 Daltons, or greater than or equal to 56,000 Daltons, or 35,000 to 100,000 Daltons and a weight average molecular weight based on polycarbonate standards of the reduced molecular weight polycarbonate in the adjusted stream is less than or equal to 80,000 Daltons, or less than or equal 45,000 Daltons, or 8,000 to 80,000 Daltons; provided that the reduced molecular weight of the polycarbonate in the adjusted stream is less than the molecular weight of the polycarbonate in the polycarbonate stream.

[0083] Aspect 20: The method of Aspect 19, wherein the weight average molecular weight of the polycarbonate is greater than or equal to 56,000 Daltons, or 56,000 to 100,000 Daltons and the weight average molecular weight of the reduced molecular weight polycarbonate is less than or equal 45,000 Daltons, or 8,000 to 45,000 Daltons.

[0084] Aspect 21: The method of any one or more of the preceding aspects, wherein the polycarbonate has a melt volume flow rate of less than or equal to 7 cm /10 min, or 3 to 7 cm³/ 10 min measured at 300°C under a load of 1.2 kg according to ASTM D1238-04 and the MVR of the reduced molecular weight polycarbonate in the adjusted stream is greater than or equal to 7 cm 3 /10 min, or 8 to 20 cm 3 /10 min measured at 300°C under a load of 1.2 kg according to ASTM D1238-04.

[0085] Aspect 22: The method of any one or more of the preceding aspects, further comprising directing the adjusted stream to an extruder.

[0086] Aspect 23: The method of any one or more of the preceding aspects, wherein a final polymerization unit is in fluid communication with an extruder via a conduit; wherein a mixing element is located along the length of the conduit to allow for mixing of the chain scission agent and the polycarbonate thus forming the adjusted stream.

[0087] As used herein, the end-capping level in percent (%EC) is determined by the following equation:

wherein ppm OH is the amount of hydroxyl end groups in parts per million by weight (ppm) and Mn is the number averaged molecular weight based on polycarbonate standards in Daltons. The ppm OH can be determined by Fourier Transform Infrared Spectroscopy (FTIR), for example, on a Perkin Elmer FTIR Spectrum One Device by dissolving 0.5 grams (g) of the polycarbonate sample in 25 milliliters (mL) of dried chloroform, measuring the absorbance at a wavelength of 3,584 inverse centimeters (cm ¹) using a univariable calibration, and normalizing the absorbance by dividing the absorbance by the absorbance at 2,779 cm^"1.

[0088] The compositions, methods, and articles can alternatively comprise, consist of, or consist essentially of, any appropriate materials, steps, or components herein disclosed. The compositions, methods, and articles can additionally, or alternatively, be formulated so as to be devoid, or substantially free, of any materials (or species), steps, or components, that are otherwise not necessary to the achievement of the function or objectives of the

compositions, methods, and articles.

[0089] The terms "a" and "an" do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced item. The term "or" means "and/or" unless clearly indicated otherwise by context. Reference throughout the specification to "an aspect", "an embodiment", "another embodiment", "some embodiments", and so forth, means that a particular element (e.g., feature, structure, step, or characteristic) described in connection with the embodiment is included in at least one embodiment described herein, and may or may not be present in other embodiments. In addition, it is to be understood that the described elements may be combined in any suitable manner in the various embodiments.

[0090] In general, the compositions, methods, and articles can alternatively comprise, consist of, or consist essentially of, any ingredients, steps, or components herein disclosed. The compositions, methods, and articles can additionally, or alternatively, be formulated, conducted, or manufactured so as to be devoid, or substantially free, of any ingredients, steps, or components not necessary to the achievement of the function or objectives of the present claims.

[0091] "Optional" or "optionally" means that the subsequently described event or circumstance may or may not occur, and that the description includes instances where the event occurs and instances where it does not. The endpoints of all ranges directed to the same component or property are inclusive of the endpoints, are independently combinable, and include all intermediate points. For example, ranges of "up to 25 wt%, or 5 to 20 wt%" is inclusive of the endpoints and all intermediate values of the ranges of "5 to 25 wt%," such as 10 to 23 wt%, etc. The suffix "(s)" as used herein is intended to include both the singular and the plural of the term that it modifies, thereby including one or more of that term (e.g., the colorant(s) includes one or more colorants). The term "combination" is inclusive of blends, mixtures, alloys, reaction products, and the like. Also, "combinations comprising at least one of the foregoing" or "at least one of means that the list is inclusive of each element individually, as well as combinations of two or more elements of the list, and combinations of at least one element of the list with like elements not named.

[0092] Unless specified to the contrary herein, all test standards are the most recent standard in effect as of the filing date of this application, or, if priority is claimed, the filing date of the earliest priority application in which the test standard appears.

[0093] Unless defined otherwise, technical and scientific terms used herein have the same meaning as is commonly understood by one of skill in the art to which this disclosure belongs.

[0094] All cited patents, patent applications, and other references are incorporated herein by reference in their entirety. However, if a term in the present application contradicts or conflicts with a term in the incorporated reference, the term from the present application takes precedence over the conflicting term from the incorporated reference.

[0095] While particular embodiments have been described, alternatives,

modifications, variations, improvements, and substantial equivalents that are or may be presently unforeseen may arise to applicants or others skilled in the art. Accordingly, the appended claims as filed and as they may be amended are intended to embrace all such alternatives, modifications variations, improvements, and substantial equivalents.

Claims

CLAIMS What is claimed is:

1. A method for the manufacture of a melt polycarbonate, comprising:

melt polymerizing a feed stream in a final polymerization unit to form a

polycarbonate stream comprising a polycarbonate;

controlling a scission stream flowrate of a chain scission stream comprising the chain scission agent; and

mixing the chain scission stream and the polycarbonate stream to form an adjusted stream comprising a reduced molecular weight polycarbonate;

wherein the controlling comprises

determining an upstream viscosity, an upstream temperature, an upstream flowrate, and an endcap level of the polycarbonate stream and controlling the scission stream flowrate based on the upstream viscosity, the upstream temperature, the upstream flow rate, and the endcap level; or

determining the upstream flow rate of the polycarbonate stream, determining a downstream viscosity and a downstream temperature of the adjusted stream, and controlling the scission stream flowrate based on the upstream flow rate, the downstream viscosity and the downstream temperature; or

determining the upstream viscosity and the upstream temperature of the polycarbonate stream, determining the downstream viscosity and the downstream

temperature of the adjusted stream, and controlling the scission stream flowrate based on the upstream viscosity, the upstream temperature, downstream viscosity, and the downstream temperature.

2. The method of Claim 1, wherein the controlling comprises determining the upstream viscosity, the upstream temperature, the upstream flow rate, and the endcap level of the polycarbonate stream.

3. The method of Claim 2, wherein the controlling comprises transmitting an upstream viscosity signal based on the upstream viscosity and the upstream temperature; transmitting an upstream flowrate signal of the polycarbonate stream based on the upstream flowrate; determining an adjustment scission stream flowrate based on the upstream viscosity signal and the upstream flowrate signal; and adjusting the scission stream flowrate to the adjustment scission stream flowrate.

4. The method of Claim 1, wherein the controlling comprises determining the downstream viscosity and the downstream temperature of the adjusted stream.

5. The method of Claim 4, wherein the controlling comprises transmitting a downstream viscosity signal based on the downstream viscosity and the downstream temperature; determining an adjustment scission stream flowrate based on the downstream viscosity signal; and adjusting the scission stream flowrate to the adjustment scission stream flowrate.

6. The method of Claim 1, wherein the controlling comprises determining the upstream viscosity and the upstream temperature of the polycarbonate stream and

determining the downstream viscosity and the downstream temperature of the adjusted stream.

7. The method of Claim 6, wherein the controlling comprises transmitting an upstream viscosity signal based on the upstream viscosity and the upstream temperature; transmitting a downstream viscosity signal based on the downstream viscosity and the downstream temperature; determining a differential between the upstream viscosity signal and the downstream viscosity signal; and adjusting the scission stream flowrate to an adjustment scission stream flowrate.

8. The method of any one or more of Claims 1 and 4 to 7, further comprising determining the upstream flowrate of the polycarbonate stream.

9. The method of any one or more of the preceding claims, further comprising directing the adjusted stream to an extruder.

10. The method of any one or more of the preceding claims, further comprising determining an endcap level of the polycarbonate stream and adjusting the scission stream flowrate based on the upstream viscosity and the endcap level.

11. The method of any one or more of the preceding claims, further comprising transmitting a polycarbonate stream pressure control signal based on the upstream viscosity to a pressure controller and adjusting a pressure in the final polymerization unit based on the polycarbonate stream pressure control signal.

12. The method of any one or more of the preceding claims, further comprising polymerizing the polycarbonate in a leading polymerization unit located upstream of the final polymerization unit to form the feed stream; and transmitting a feed stream pressure control signal from a feed stream viscometer to a polymerizer pressure controller and adjusting a pressure in a leading polymerization unit based on the feed stream pressure control signal.

13. The method of any one or more of the preceding claims, wherein a measured weight average molecular weight of the reduced molecular weight polycarbonate in the adjusted stream at any given time during the polymerization is within 5% of an average weight average molecular weight of the reduced molecular weight polycarbonate; and/or wherein a weight average molecular weight based on polycarbonate standards of the reduced molecular weight polycarbonate varies by plus or minus 500 Daltons.

14. The method of any one or more of the preceding claims, wherein a weight average molecular weight based on polycarbonate standards of the polycarbonate in the polycarbonate stream is greater than or equal to 35,000 Daltons and a weight average molecular weight based on polycarbonate standards of the reduced molecular weight polycarbonate in the adjusted stream is less than or equal to 80,000 Daltons; wherein the reduced molecular weight of the polycarbonate in the adjusted stream is less than the molecular weight of the polycarbonate in the polycarbonate stream.

15. The method of any one or more of the preceding claims, wherein the chain scission agent comprises at least one of a carbonate source, water, or an aryl alcohol, preferably, wherein the chain scission agent comprises at least one of a diphenyl carbonate, methyl phenyl carbonate, dimethyl carbonate, diethyl carbonate, ethyl phenyl carbonate, or phenol.

16. The method of any one or more of the preceding claims, wherein the polycarbonate comprises a bisphenol A polycarbonate and the chain scission agent comprises diphenyl carbonate.