PROCESS FOR PREPARING POLYCARBONATES BY TRANSESTERIFYING DITHIOCARBONATES OR SELENIUM ANALOGUES THEREOF WITH BISPHENOLS

Abstract

The present invention relates to a process for preparing aromatic polycarbonates, comprising the step of reacting bisphenols with dithiocarbonates or selenium analogues thereof in the presence of a catalyst. It further relates to the use of dithiocarbonates or selenium analogues thereof as transesterifying reagents for the preparation of polycarbonates.

Claims

1. A process for preparing polycarbonates, comprising reacting bisphenols with a transesterifying reagent in the presence of a catalyst, wherein the transesterifying reagent comprises a compound of the general formula (I):
RXC(O)XR(I) wherein X and X are each independently S or Se, and R and R are each independently alkyl or aryl or R and R together are an alkylene chain.

2. The process according to claim 1, wherein X and X in the general formula (I) are S.

3. The process according to claim 1, wherein the compounds RXH and RXH formed during the reaction are removed continuously.

4. The process according to claim 1, wherein the reaction is conducted for a first period of time at a first temperature and a first pressure and then for a second period of time at a second temperature and a second pressure, and wherein the second temperature is greater than the first temperature and the second pressure is lower than the first pressure.

5. The process according to claim 4, wherein the first temperature is 150 C. to 210 C. and the second temperature is 210 C. to 400 C.

6. The process according to claim 4, wherein the first pressure is 200 mbar to 900 mbar and the second pressure is 1 mbar to 200 mbar.

7. The process according to claim 4, wherein the reaction conducted for the second period of time at the second temperature and the second pressure is conducted in an evaporating extruder, a disc reactor or an evaporating calender.

8. The process according to claim 1, wherein R and R in the general formula (I) are methyl, ethyl or phenyl.

9. The process according to claim 1, wherein the transesterifying reagent is a dialkyl dithiocarbonate.

10. The process according to claim 1, wherein the polyols used include bisphenol A, bisphenol F, or bisphenol TMC.

11. The process according to claim 1, wherein the catalyst is a phosphonium salt or a bicyclic amine.

12. The process according to claim 1, wherein the catalyst is added in two or more portions over the course of the reaction.

13. The process according to claim 1, further comprising adding a diaryl carbonate or dialkyl carbonate to the reaction product obtained.

14. A transesterifying reagent for the preparation of polycarbonates comprising a compound of the general formula (I):
RXC(O)XR(I), wherein X and X are S or Se, and R and R are each independently alkyl or aryl or R and R together are an alkylene chain.

15. The process according to claim 5, wherein the first pressure is 200 mbar to 900 mbar and the second pressure is 1 mbar to 200 mbar.

Description

EXAMPLES

[0065] The present invention is illustrated in detail by the examples and comparative examples which follow, but without being restricted thereto.

[0066] Transesterifying reagents used:

[0067] Dimethyl dithiocarbonate S,S-dimethyl dithiocarbonate

[0068] Dimethyl carbonate O,O-dimethyl carbonate

[0069] Bisphenols used:

[0070] Bisphenol A 2,2-bis(4-hydroxyphenyl)propane

[0071] Polycarbonates used as reference substance: [0072] Makrolon Aromatic homopolycarbonate based on bisphenol A from Bayer MaterialScience AG having a number-average molecular weight of M.sub.n=13 900 g/mol and a polydispersity of 2.4.

[0073] The polymerization reaction of bisphenol A with dimethyl dithiocarbonate gives a linear polycarbonate which, as possible end groups, contains the free OH groups shown in the formula (Xa)

##STR00003##

and/or the unsymmetric thioesters shown in formula (Xb)

##STR00004##

and/or the alkylated phenol groups shown in formula (Xc)

##STR00005##

[0074] In the case of addition of diphenyl carbonate (cf. Example 3), what is obtained is a polycarbonate containing, as possible end groups, additionally or exclusively the monofunctional phenol groups shown in formula (Xd)

##STR00006##

[0075] The linear polymeric molecules usually contain two end groups of the formulae (Xa) to (Xd), where each molecule may contain two identical or two different end groups.

[0076] Each sample was dissolved in deuterated chloroform and analysed on a Bruker spectrometer (AV400, 400 MHz). The degree of functionalization of the bisphenol A was determined by means of .sup.1H NMR spectroscopy. For this purpose, the intensities of the different resonances were integrated with respect to one another.

[0077] The relevant resonances in the .sup.1H NMR spectrum (based on TMS=0 ppm) which were used for integration are as follows: [0078] I1: 1.59: CH.sub.3 groups of the repeat bisphenol A units [0079] I2: 2.32: CH.sub.3 group of the unsymmetric thioester (Xb) [0080] I3: 3.69: CH.sub.3 group of the alkylated phenol (Xc) [0081] I4: 6.57-6.60 and 6.96-6.99: aromatic CH groups on bisphenol A and phenyl rings of terminal bisphenol A units with directly bonded free OH groups (Xa) [0082] I5: 7.07-7.09 and 7.16-7.18: aromatic CH groups of bisphenol A-based repeat units and phenyl rings of terminal bisphenol A units without directly bonded free OH groups (Xa)

[0083] The figure for the degree of functionalization of the bisphenol A unit is based on the proportion of phenol groups converted in the bisphenol A used and is given in mol %. Taking account of the relative intensities, the values were calculated as follows:

Degree of functionalization=I5/(I4+I5)

[0084] The number-average molecular weight M.sub.n and the weight-average molecular weight M.sub.w of the resulting polymers were determined by means of gel permeation chromatography (GPC). The procedure of DIN 55672-1 was followed: Gel permeation chromatography, Part 1Tetrahydrofuran as eluent (SECurity GPC System from PSS Polymer Service, flow rate 1.0 ml/min; columns: 2PSS SDV linear M, 8300 mm, 5 m; RID detector). Polystyrene samples of known molar mass were used for calibration.

[0085] The reaction of bisphenol with a transesterifying reagent was conducted in a Schlenk tube with attached reflux condenser. The Schlenk tube was heated externally with an electrical heating mantle which was kept at the temperature specified by closed-loop control. The reaction mixture was stirred by means of a magnetic stirrer bar within the reaction mixture.

Example 1: Reaction of Bisphenol A with Dimethyl Dithiocarbonate in a One-Stage Process

[0086] To bisphenol A (5.71 g, 25.0 mmol) in a 100 ml Schlenk tube with attached reflux condenser were added dimethyl dithiocarbonate (3.05 g, 25.0 mmol) and tetraphenylphosphonium phenoxide (216 mg, 2.0 mol % based on carbonate used). Subsequently, the reaction mixture was heated with an electrical heating mantle to 200 C. at a pressure of 750 mbar for 6 hours.

[0087] 6.62 g of a viscous material were obtained.

[0088] .sup.1H NMR analysis in the region of the aromatic hydrogens (5.5-8.5 ppm) showed 75% functionalization of the bisphenol A.

[0089] GPC analysis of the product gave a number-average molecular weight of M.sub.n=570 g/mol and a polydispersity of 3.53.

Example 2: Reaction of Bisphenol A with Dimethyl Dithiocarbonate in a Two-Stage Process

[0090] To bisphenol A (5.71 g, 25.0 mmol) in a 100 ml Schlenk tube with attached reflux condenser were added dimethyl dithiocarbonate (4.88 g, 40.0 mmol) and tetraphenylphosphonium phenoxide (85 mg, 2.0 mol % based on carbonate used). Subsequently, the reaction mixture was heated in two stages. First, the mixture was heated to 250 C. under reflux at a pressure of 500 mbar for one hour. Subsequently, the reflux condenser was exchanged for a distillation system. The reaction mixture was still heated to 250 C., in the course of which an argon stream was first passed through the reaction mixture for one hour and then the pressure was reduced to 10 mbar for 30 minutes. Subsequently, the vessel was closed and the reaction mixture was heated to 300 C. at a pressure of <1 mbar for 2 hours. In the course of this, a brownish precipitate sublimed on the upper walls of the vessel. No yield was determined.

[0091] .sup.1H NMR analysis in the region of the aromatic hydrogens (5.5-8.5 ppm) showed complete functionalization of the bisphenol A.

[0092] GPC analysis of the product gave a number-average molecular weight of M.sub.n=1700 g/mol and a polydispersity of 1.94.

Example 3: Reaction of Bisphenol A with Dimethyl Dithiocarbonate in a Two-Stage Process and Addition of Diphenyl Carbonate to Reduce the Content of Thioester and OH Groups in the Product

Polymerization

[0093] To bisphenol A (5.71 g, 25.0 mmol) in a 100 ml Schlenk tube with attached reflux condenser were added dimethyl dithiocarbonate (4.27 g, 35.0 mmol) and tetraphenylphosphonium phenoxide (76 mg, 0.5 mol % based on carbonate used). Subsequently, the reaction mixture was heated in stages. First, the mixture was heated to 220 C. under reflux at a pressure of 400 mbar for one hour. Subsequently, the reflux condenser was exchanged for a distillation system. The reaction mixture was heated at a pressure of 10 mbar for one hour, with stepwise increases in temperature after 20 minutes in each case from 220 C. to 260 C. and then 300 C.

Addition of Diaryl Carbonate or Dialkyl Carbonate

[0094] Then diphenyl carbonate was added (DPC, 428 mg, 2 mmol). Subsequently, the vessel was closed and the reaction mixture was heated to 300 C. under a pressure of <1 mbar for 1 hour.

[0095] .sup.1H NMR analysis in the region of the aromatic hydrogens (5.5-8.5 ppm) showed 85% functionalization of the bisphenol A after the first reaction step. The .sup.1H NMR analysis of the product corresponded to Makrolon in all aspects.

[0096] GPC analysis of the product gave a number-average molecular weight of M.sub.n=11 300 g/mol and a polydispersity of 4.340.

[0097] 5.62 g of polycarbonate were obtained (87.8% yield).

Example 4 (Comparative Example): Reaction of Bisphenol A with Dimethyl Carbonate

[0098] To bisphenol A (5.71 g, 25.0 mmol) in a 100 ml Schlenk tube with attached reflux condenser were added dimethyl carbonate (3.15 g, 35.0 mmol) and tetraphenylphosphonium phenoxide (76 mg, 0.5 mol % based on carbonate used). Subsequently, the reaction mixture was heated at a pressure of 400 mbar. Strong reflux was observed; there was likewise formation of a white solid in the flask. The temperature of the reaction mixture rose to a maximum temperature of 73 C. within one hour.

[0099] Analysis of the product mixture by .sup.1H NMR in the range of the aromatic hydrogens (5.5-8.5 ppm) showed that the reaction mixture contained mainly (>60%) unconverted bisphenol A as well as unconverted dimethyl carbonate.

TABLE-US-00001 TABLE 1 Comparison of the results of Inventive Examples 1-3 with Comparative Example 4 Degree of Molecular weight functionalization of the product of bisphenol obtained Poly- Example Process A [%] [g/mol] dispersity 1 one-stage 75 570 3.53 2 two-stage 100 1700 1.94 3 two-stage 100 11 300 4.34 4 one-stage 40 (comp.)

[0100] Comparison of Examples 1 to 3 with Comparative Example 4 shows that use of a dichalcogenide carbonate as transesterifying reagent affords an oligomeric polycarbonate (Example 1) or polymeric polycarbonate (Examples 2 and 3), whereas, in the case of use of dimethyl carbonate as transesterifying reagent (Comparative Example 4), bisphenol A is reacted with dimethyl carbonate only in a low yield and no polycarbonate is obtained.

Example 5: Reaction of Bisphenol A with Dimethyl Dithiocarbonate in a Two-Stage Process

[0101] To bisphenol A (5.71 g, 25.0 mmol) in a 100 ml Schlenk tube with attached reflux condenser were added dimethyl dithiocarbonate (4.88 g, 40.0 mmol) and tetraphenylphosphonium phenoxide (85 mg, 0.5 mol % based on carbonate used). Subsequently, the reaction mixture was heated in stages. First, the mixture was heated to 220 C. under reflux at a pressure of 400 mbar for one hour. Subsequently, the reflux condenser was exchanged for a distillation system. The reaction mixture was heated at a pressure of 10 mbar for one hour, with stepwise increases in temperature after 20 minutes in each case from 220 C. to 260 C. and then 300 C. Subsequently, the vessel was closed and the reaction mixture was heated to 300 C. at a pressure of <1 mbar for 1 hour.

[0102] 5.85 g of polycarbonate were obtained (91.4% yield).

[0103] GPC analysis of the product gave a number-average molecular weight of M.sub.n=10 000 g/mol and a polydispersity of 2.92.

[0104] .sup.1H NMR analysis in the region of the aromatic hydrogens (5.5-8.5 ppm) showed 90% functionalization of the bisphenol A after the first reaction step. The .sup.1H NMR analysis of the product corresponded to Makrolon in all significant aspects.

[0105] A gel permeation chromatogram (GPC) of the polycarbonate obtained in comparison with Makrolon is shown in FIG. 1. Curve 1 is for Makrolon, curve 2 for the polymer sample according to the invention.

Example 6: Reaction of Bisphenol a with Dimethyl Dithiocarbonate in a Two-Stage Process

[0106] To bisphenol A (5.71 g, 25.0 mmol) in a 100 ml Schlenk tube with attached reflux condenser were added dimethyl dithiocarbonate (4.88 g, 40.0 mmol) and 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU, 60 mg, 1.0 mol % based on carbonate used). Subsequently, the reaction mixture was heated in stages. First, the mixture was heated to 250 C. under reflux at a pressure of 500 mbar for one hour. Subsequently, the reflux condenser was exchanged for a distillation system. The reaction mixture was heated at a pressure of 10 mbar for one hour, in the course of which the reaction mixture was first heated to 250 C. for half an hour and then to 300 C. for a further half hour. Subsequently, the vessel was closed and the reaction mixture was heated to 300 C. at a pressure of <1 mbar for 1 hour.

[0107] 6.31 g of polycarbonate were obtained (98.6% yield).

[0108] GPC analysis of the product gave a number-average molecular weight of M.sub.n=3700 g/mol and a polydispersity of 2.37.

[0109] .sup.1H NMR analysis in the region of the aromatic hydrogens (5.5-8.5 ppm) showed 90% functionalization of the bisphenol A after the first reaction step. The .sup.1H NMR analysis of the product corresponded to Makrolon in all significant aspects.

Comparison

[0110]

TABLE-US-00002 Amount of Degree of Molecular weight catalyst functionalization of the product used of bisphenol obtained Poly- Example Catalyst [mol %]* A [%] [g/mol] dispersity 3 tetraphenyl- 2.0 100 11 300 4.34 phosphonium phenoxide 5 tetraphenyl- 0.5 >95 10 000 2.92 phosphonium phenoxide 6 DBU 1.0 ~95 3700 2.37 *mol % based on carbonate

[0111] A comparison of Examples 3, 5 and 6 shows that, for the reaction of the dichalcogenide carbonate with bisphenol A, it is possible to use tetraarylphosphonium arylates (Examples 3 and 5) and bicyclic amine compounds (Example 6) as catalyst.

Example 7: Reaction of Bisphenol A with Dimethyl Dithiocarbonate in a Two-Stage Process

[0112] To bisphenol A (5.71 g, 25.0 mmol) in a 100 ml Schlenk tube with attached reflux condenser were added dimethyl dithiocarbonate (4.88 g, 40.0 mmol) and tetraphenylphosphonium phenoxide (85 mg, 0.5 mol % based on carbonate used). Subsequently, the reaction mixture was heated in stages. First, the mixture was heated to 200 C. under reflux at a pressure of 750 mbar for one hour. Subsequently, the reflux condenser was exchanged for a distillation system. The reaction mixture was heated at a pressure of 10 mbar for one hour, in the course of which the temperature was kept at 200 C. for 30 minutes and then increased stepwise to 250 C. and then 300 C. for 15 minutes in each case. Subsequently, the vessel was closed and the reaction mixture was heated to 300 C. at a pressure of <1 mbar for 1 hour.

[0113] 5.56 g of polycarbonate were obtained (86.9% yield).

[0114] GPC analysis of the product gave a number-average molecular weight of M.sub.n=6500 g/mol and a polydispersity of 2.48.

[0115] .sup.1H NMR analysis in the region of the aromatic hydrogens (5.5-8.5 ppm) showed 80% functionalization of the bisphenol A after the first reaction step. The .sup.1H NMR analysis of the product corresponded to Makrolon in all significant aspects.

Comparison

[0116]

TABLE-US-00003 Molecular weight of the product obtained Poly- Example 1st stage 2nd stage 3rd stage [g/mol] dispersity 5 400 mbar, 10 mbar, <1 mbar, 10 000 2.92 220 C. 220 .fwdarw. 300 C. 300 C. 7 750 mbar, 10 mbar, <1 mbar, 6500 2.48 200 C. 200 .fwdarw. 300 C. 300 C.

[0117] A comparison of Examples 5 and 7 shows that it is possible to use different temperatures and pressure levels for the reaction of the dichalcogenide carbonate with bisphenol A.

[0118] FIG. 2 shows a comparison of the gel permeation chromatograms of Makrolon (curve 3) and the reaction product obtained from a polymerization of bisphenol A with dimethyl dithiocarbonate without addition of DPC (Example 5) after various reaction times (curve 4: 2 hours, curve 5: 3 hours) and the reaction product obtained from a reaction with addition of DPC (Example 3) after a reaction time of 2 hours at various reaction times (curve 6: 2 hours, immediately prior to addition of DPC; curve 7: 3 hours, after complete polymerization). The increase in the molecular weight as a result of the DPC addition is clearly apparent.