KR19990045077A - Method for producing polycarbonate by solid phase polymerization - Google Patents

Abstract

Crystallization of the polycarbonate precursor prior to solid phase polymerization is achieved by contacting at least in part with a non-solvent comprising a dialkyl carbonate such as dimethyl carbonate. The nonsolvent is typically a mixture of dimethyl carbonate and alkanols such as water or methanol.

Description

Method for producing polycarbonate by solid phase polymerization

The present invention relates to the production of polycarbonates and more particularly to their preparation by solid phase polymerization.

Solid phase polymerizations are disclosed, for example, in US Pat. Nos. 4,948,871, 5,204,377, and 5,214,073, which are incorporated herein by reference. This includes three steps: a first step, typically by melt polymerizing (ie, transesterifying) a dihydroxyaromatic compound, such as bisphenol A, with a diaryl carbonate, such as diphenyl carbonate; A second step of crystallizing the prepolymer; And increasing the molecular weight of the crystallized prepolymer by heating to a temperature between its glass transition temperature and its melting temperature. The use of this method is of increasing interest due to its effectiveness and environmental benefits.

The aforementioned US Pat. No. 5,204,377 describes a solid phase polymerization process which requires the use of crystallized prepolymers having a specific surface area of at least 0.2 m ² / g. This is difficult to accomplish because of the very high surface area and, for example, high shear conditions. Therefore, it is of interest to develop solid phase polymerization processes that do not require crystallized prepolymers having such high surface areas.

The present invention provides a solid phase polymerization process that is easily carried out and eliminates the hassle of intermediate surface area requirements. In particular, high molecular weight polycarbonates can be prepared using crystallized prepolymers having a relatively low surface area.

The present invention is a process for producing an aromatic polycarbonate comprising:

(A) contacting a solid, amorphous aromatic polycarbonate precursor with one or more organic nonsolvents for the precursor, including one or more dialkylcarbonates, to form a surface crystallized polycarbonate; And

(B) polymerizing the surface crystallized polycarbonate by solid phase polymerization.

Polycarbonates that may be prepared by the process of the invention typically have structural units of the formula

Where

At least about 60% of the total number of R groups are aromatic organic radicals, with the remainder being aliphatic, cycloaliphatic or aromatic radicals. Preferably, each R is an aromatic organic radical, even more preferably is of the formula -A ¹ -YA ^2- , wherein A ¹ and A ² are each monocyclic divalent aryl radicals, and Y is one or two Carbonate atom is a crosslinking radical which divides A ¹ and A ² ). These radicals are derived from dihydroxyaromatic compounds of the general formulas HO-R-OH and HO-A ¹ -YA ² -OH, respectively. For example, A ¹ and A ² generally represent unsubstituted phenylene (particularly p-phenylene is preferred) or substituted derivatives thereof. The bridging radicals Y are usually hydrocarbon groups and in particular saturated groups such as methylene, cyclohexylidene or preferably isopropylidene. Thus, the most preferred polycarbonates are those derived from 2,2-bis (4-hydroxyphenyl) propane in whole or in part also known as "bisphenol A".

The essential starting material in step A of the process of the invention is a polycarbonate precursor. This may be the first step of the melt polycarbonate process, or polycarbonate oligomers of the type prepared by hydrolysis and / or endcapping and separation after preparation of the bischloroformate oligomer. Such oligomers usually have an intrinsic viscosity in the range of about 0.06 to 0.30 dl / g, and all intrinsic viscosity values herein are measured in chloroform at 25 ° C.

The polycarbonate precursor may be a branched polycarbonate formed by reacting a linear polycarbonate or precursor (s) thereof with a branching agent such as 1,1,1-tris (4-hydroxyphenyl) ethane. It may also be copolycarbonates, in particular copolycarbonate oligomers or high molecular weight copolycarbonates, containing units adjusted to maximize solvent resistance. Hydroquinone and methylhydroquinone carbonate units are particularly suitable for this purpose as disclosed in US Pat. No. 4,920,200. Such units will typically make up about 25-50% of the total carbonate of the polymer. Conversion to branched polycarbonates or copolycarbonates can occur prior to or simultaneously with the conversion of the polycarbonate precursors into improved crystallinity polymers.

The polycarbonate precursor may also be recycled polycarbonate. For example, polymers recycled from compact discs can be used. Its original method of manufacture is not important; That is, recycled polycarbonates originally produced by interfacial polymerization, melt polymerization or prepared from bischloroformates can be used.

Such recycled materials typically have a degraded molecular weight than the molecular weight of the original polymerized material, exhibiting an intrinsic viscosity in the range of about 0.25 to 1.0 dl / g. It is dissolved in chlorinated organic solvents such as chloroform, methylene chloride or 1,2-dichloroethane and then scrap polycarbonate by other recognized procedures for filtration of insoluble materials or for separation of nonpolycarbonate components. Can be obtained from. Other types of polycarbonates, such as interfacial polycarbonates and polycarbonate compressor shavings, can also be used as precursors.

Prior to performing step A, it is within the scope of the present invention to dissolve it in chlorinated hydrocarbons as a solvent, especially when the carbonate precursor is a recycled material. Examples of chlorinated hydrocarbons are methylene chloride, chloroform, 1,2-dichloroethane, chlorobenzene and o-dichlorobenzene. Chloroaliphatic hydrocarbons are preferred, and methylene chloride and 1,2-dichloroethane are most preferred.

The polycarbonate precursor can be dissolved in the solvent at any temperature. Typical temperatures are from about 0 ° C. to the boiling point of the solvent, with about 20-100 ° C. generally preferred. As long as an effective amount of solvent is used to dissolve the polycarbonate, the proportion thereof is not critical.

Dissolution of the polycarbonate precursor leaves several insoluble materials such as, for example, metal coatings when the polycarbonate precursor is obtained from the optical disk. The present invention further contemplates the removal of the insoluble material from the polycarbonate solution. This can be done by conventional operations such as decantation, filtration and centrifugation.

Polycarbonate precursors are often combined with colored impurities, which can appear in the polycarbonate itself or in its solution in chlorinated solvents. Accordingly, several embodiments of the present invention include removing color from an amorphous polycarbonate solution and then performing another removal step. One method of color emission is treatment with an inorganic acid, preferably hydrochloric acid, in the solution, where the acid is typically a solution in an alkanol such as methanol. Another method is to contact the solution with a solid absorbing solid, such as activated carbon or crosslinked resin, which may be neutral or ion exchange resin. Another method is to wash with a solution of sodium gluconate. Another method is to wash the resin with an amount of nonsolvent sufficient to dissolve the color after precipitation, as described below.

Many commercially used polycarbonates are end capped with monohydroxyaromatic compounds such as phenol or p-cumylphenol. Such endcapping agents, when present, can inhibit solid phase polymerization. Thus, it is often desirable to add hydroxy end groups by adding one or more dihydroxyaromatic or dihydroxyaliphatic compounds as modifiers during the dissolution step. Suitable compounds include resorcinol, hydroquinone, methylhydroquinone, catechol, bisphenol, ethylene glycol, propylene glycol, pentaerythritol, glycerol, glyceryl monopalmitate and glyceryl monostearate, catechol and bisphenol A is often preferred.

The proportion of modifiers is generally above the ratio which is theoretically effective to convert the amorphous polycarbonate in solution to a material having about 20 to 80% (eg, allowances), preferably about 40 to 60% of hydroxy end groups. The suitable ratio can be determined by simple experiments.

In step A, the polycarbonate precursor, which may be a solid or a solution prepared by the steps described above, is contacted with one or more organic nonsolvents therefor. The nonsolvent comprises one or more dialkyl carbonates, which can be used alone or in combination with another nonsolvent. Suitable dialkyl carbonates are those in which the alkyl groups exemplified by dimethyl carbonate and diethyl carbonate have from 1 to 4 carbon atoms. Dimethyl carbonate is generally preferred due to its relative availability and low cost and particular suitability.

When dialkyl carbonates are used in combination with another nonsolvent, the other nonsolvent is typically water or a lower alcohol, and the term "lower" refers to an alkyl radical having up to 7 carbon atoms. Preferred lower alkanols are those containing 1 to 4 carbon atoms, in particular methanol and ethanol, preferably methanol.

Dialkyl carbonates are generally present in any non-solvent mixture in a main ratio, ie a ratio of at least 50% by volume. Preferably, the dialkyl carbonate comprises at least about 65 volume percent, more preferably about 65 to 85 volume percent, and most preferably about 65 to 75 volume percent.

These preferences are based, at least in part, on the physical form of the surface crystallized polycarbonate, which is the product of step A, particularly when produced from pellets of the type typically generated by commercial extrusion equipment and the like. Preference is given to the preparation of surface crystallized polycarbonates in pellet form on their own with little or no powder formation. It is also preferred that the pellets and any related powders flow freely rather than adhered to the aggregates by adhesion or agglomeration. In the more preferred and most preferred range of nonsolvent compositions, powder formation, adhesion and agglomeration are minimized.

Surface crystallization may be accomplished by merely contacting the polycarbonate precursor with the nonsolvent composition, typically at a temperature in the range of about 20 to 50 ° C. The weight ratio of nonsolvent to polycarbonate precursor is not critical but may be adjusted for convenience; A ratio in the range of about 4 to 6: 1 is typical.

As described in the aforementioned patent and co-pending and generally owned application 08 / 767,740, the surface crystallization step can be in the absence or presence of a catalyst. Suitable catalysts (if used) include alkali metal and alkaline earth metal hydroxides, hydrides, borohydrides, aluminum hydrides and aryloxides; Compounds of elements such as zinc, boron, silicon, germanium, tin and lead; Onium compounds such as quaternary ammonium and quaternary phosphonium salts, including carboxylates such as maleate; Antimony, manganese, titanium and zirconium compounds; And nonoxyanionic carboxylates and phenoxides. Catalyst ratios typically range from about 50 to 200 ppm based on the polycarbonate precursor in use.

Contrary to the disclosure shown above in US Pat. No. 5,204,377, it has been found that the surface crystallized polycarbonates produced in step A of the process of the invention do not have particularly high surface areas. More specifically, the surface area is generally not more than 0.2 m ² / g previously considered necessary or desirable. Nevertheless, the surface crystallized polycarbonate can be easily polymerized by solid phase polymerization.

In addition, contrary to the description in the previously mentioned US Pat. No. 4,948,871 that a total crystallinity of at least 5% is required for solid state polymerization, the overall crystallinity of the surface crystallized polycarbonate is not considered important for its usability. From experience, all that is needed is a significant, typically at least 5% surface crystallinity. Thus, the crystallinity or amorphousness of the inner region of the polycarbonate does not appear to have a significant effect on its degree of polymerization in the solid phase.

Step B is a solid phase polymerization operation. This can be done under conditions recognized in the art. These conditions include a temperature between the glass transition temperature and the melting temperature of the surface crystallized polycarbonate, usually 10 to 50 ° C. lower than its melting temperature. In general, temperatures in the range of about 150 to 270 ° C., in particular about 180 to 250 ° C., are particularly suitable for bisphenol A homopolycarbonates. Although no catalyst is required, any catalyst used in step A will usually still be present and its presence is not harmful.

The method of the present invention is illustrated by the following examples. Intrinsic viscosity was measured in methylene chloride at 20 ° C.

Example 1

In a 250 ml round bottom flask equipped with an addition funnel, reflux condenser and agitator, 20 g of bisphenol A polycarbonate with an intrinsic viscosity of 0.16 dl / g, 100 ml of dimethyl carbonate and 100 ppm of tetramethylammonium hydrogen maleate (based on oligomer) Load. After the mixture was stirred at 27 ° C. for 10 minutes, dimethyl carbonate was removed by distillation under reduced pressure and the residue was dried at 80 ° C. for 2-3 hours. The solid material was filtered and particles passed through a 25 mesh screen. The resulting surface crystallized polycarbonate oligomer had an intrinsic viscosity of 0.16 dl / g, a glass transition temperature of 115 ° C., a melting temperature of 231 ° C. and a crystallinity of 33%.

Surface crystallized oligomers were exposed under solid state polymerization conditions at 180 ° C. for 1 hour, 210 ° C. for 1 hour, 220 ° C. for 2 hours and 230 ° C. for 2 hours in a fluidized bed reactor under nitrogen flow. The resulting polycarbonate had an inherent viscosity of 0.55 dl / g, a glass transition temperature of 147 ° C. and a melting temperature of 250 ° C.

Example 2

The polycarbonate oligomer was replaced with pelletized commercial bisphenol A polycarbonate having an intrinsic viscosity of 0.36 dl / g, and (Examples 3 to 5) dimethyl carbonate was replaced with several mixtures of dimethyl carbonate and methanol The process was repeated. The surface crystallized polycarbonate had an intrinsic viscosity of 0.36 dl / g, a glass transition temperature of 134 ° C., a melting temperature of 234 ° C. and a crystallinity of 32%. The polycarbonate obtained by the solid phase polymerization had an inherent viscosity of 0.55 dl / g, a glass transition temperature of 149 ° C and a melting temperature of 261 ° C.

Examples 3 to 5

The procedure of Example 2 was repeated replacing dimethyl carbonate with several dimethyl carbonate-methanol. The results are given in the following table; PC is polycarbonate, SSP is solid state polymerized and Tm is melting temperature.

Example Methanol, volume% Surface crystallized PC SSP PC Tm, ℃ Crystallinity,% Adhesion / Bundling powder, % 3 10 224 25 ○ 10 4 20 217 23 ○ 3 5 30 218 20 × One

Example 6

100 g of a sample of bisphenol A polycarbonate recovered from the extruder drip is dissolved in 700 ml of 1,2-dichloroethane at 80 ° C. with vigorous stirring. The solution is centrifuged and the solid residue is removed and discarded. Dimethyl carbonate was added to the polycarbonate solution to precipitate the polycarbonate as a crystalline solid, separated and washed with ethyl acetate until colorless, and dried in vacuo at 80 ° C. The resulting surface crystallized polycarbonate can be solid-phase polymerized by the method of Example 2.

According to the present invention, the solid phase polymerization can be easily solid phase polymerization that does not require a high surface area.

Claims (13)

(A) contacting the solid, amorphous aromatic polycarbonate precursor with at least one organic nonsolvent for the precursor, including at least one dialkylcarbonate, to form a surface crystallized polycarbonate; And (B) polymerizing the surface crystallized polycarbonate by solid phase polymerization. The method of claim 1, The dialkyl carbonate is dimethyl carbonate. The method of claim 2, Wherein the polycarbonate comprises a structural unit of formula Formula 1 Where At least about 60% of the total number of R groups is an aromatic organic radical, The remainder are aliphatic, cycloaliphatic or aromatic radicals. The method of claim 3, wherein Wherein the polycarbonate is bisphenol A homopolycarbonate. The method of claim 2, Wherein the nonsolvent consists of dimethyl carbonate. The method of claim 2, The nonsolvent is a mixture of dimethyl carbonate and water or lower alkanols. The method of claim 6, The nonsolvent is methanol. The method of claim 7, wherein And the dialkyl carbonate constitutes about 65 to 85% by volume of the nonsolvent. The method of claim 8, And the dialkyl carbonate constitutes about 65 to 75% by volume of the nonsolvent. The method of claim 2, Method A is carried out in the presence of a catalyst. The method of claim 10, The catalyst is a quaternary ammonium or quaternary phosphonium salt. The method of claim 11, The catalyst is a quaternary ammonium carboxylate. The method of claim 12, The catalyst is tetramethylammonium hydrogen maleate.