Preparation of siloxane-containing block copolycarbonates by means of reactive extrusion

Abstract

The present invention relates to a process for preparing polysiloxane-polycarbonate block cocondensates proceeding from specific polycarbonates and hydroxyaryl-terminated polysiloxanes. More particularly, the present invention relates to the preparation of the said block cocondensates by means of a reactive extrusion.

Claims

1. A process for preparing polysiloxane-polycarbonate block cocondensates, comprising reacting at least one hydroxyaryl-terminated polydialkylsiloxane with at least one polycarbonate in the melt, wherein the process is conducted in at least two stages in a reactor combination consisting of at least one preliminary reactor and a high-viscosity reactor and a discharge unit, wherein the material temperature in the high-viscosity reactor is within the range of from 330° C. to 370° C. and the pressure is within the range of from 0.03 to 5 mbar.

2. The process according to claim 1, wherein the preliminary reactor consists of a single- or twin-screw extruder.

3. The process according to claim 1, wherein the high-viscosity reactor has two or more shafts which rotate in parallel, on which there are axially offset, circular discs with strippers distributed on the circumference thereof.

4. The process according to claim 1, wherein the discharge unit used is a single-screw screw, twin-screw screw or a gear pump.

5. The process according to claim 1, wherein the material temperature in the preliminary reactor is within the range of from 300° C. to 380° C. and the pressure in the preliminary reactor is at least temporarily within the range of from 200 to 0.1 mbar.

6. The process according to claim 1, wherein the residence time in the high-viscosity reactor is less than 50 minutes.

7. The process according to claim 1, wherein the polycarbonate has a weight-average molecular weight of 16 000 to 28 000 g/mol and an OH end group content of 300 to 900 ppm.

8. The process according to claim 1, wherein the hydroxyaryl-terminated polydialkylsiloxane has the structure (1) ##STR00008## in which R.sup.1 is H, Cl, Br or C.sub.1 to C.sub.4-alkyl, R.sup.2 and R.sup.3 are the same or different and each independently from one another selected from aryl, C.sub.1 to C.sub.10-alkyl and C.sub.1 to C.sub.10-alkylaryl, X is a single bond, —CO—, —O—, C.sub.1 to C.sub.6-alkylene, C.sub.2 to C.sub.5-alkylidene, C.sub.5 to C.sub.12-cycloalkylidene or C.sub.6 to C.sub.12-arylene which may optionally be fused to further aromatic rings containing heteroatoms, n is a number from 1 to 500, m is a number from 1 to 10, and p is 0 or 1.

9. The process according to claim 8, wherein n is a number from 10 to 100 and m is a number from 2 to 5.

10. The process according to claim 1, wherein the hydroxyaryl-terminated polydialkylsiloxane has a weight-average molecular weight of 3000-20 000 g/mol.

11. The process according to claim 1, wherein a phosphonium catalyst of the formula of the formula (5) is used during the reaction: ##STR00009## where R.sup.a, R.sup.b, R.sup.c and R.sup.d may be identical or different C.sub.1-C.sub.10-alkyls, C.sub.6-C.sub.14-aryls, C.sub.7-C.sub.15-arylalkyls or C.sub.5-C.sub.6-cycloalkyls, and Y- may be an anion selected from the group consisting of hydroxide, sulphate, hydrogensulphate, hydrogencarbonate, carbonate, halide or an alkoxide or aroxide of the formula -OR.sup.e where R.sup.e is C.sub.6-C.sub.14-aryl, C.sub.7-C.sub.15-arylalkyl or C.sub.5-C.sub.6-cycloalkyl.

12. The process according to claim 1, wherein the catalyst used is tetraphenylphosphonium phenoxide.

13. The process according to claim 1, wherein the hydroxyaryl-terminated polydialkylsiloxane is used in an amount of 2 to 20%, based on the polycarbonate used.

14. The process according to claim 1, wherein the siloxane and the polycarbonate are reacted in the presence of at least one organic or inorganic salt of an acid having a pK.sub.A value within the range of from 3 to 7 (25 ° C.).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows a schematic representation of a setup for the preparation of siloxane-containing block copolycarbonates according to the invention. Polycarbonate and eventually a catalyst masterbatch of polycarbonate are metered via gravimetric feeders (4) and (5) to an extruder (1). Preferably a co-rotating twin-screw extruder exhibiting one or more vent sections is used. The screw configuration is designed according to the state of the art and is therefore not shown, The polysiloxane block is stored in a storage tank (6) and is metered to the extruder via a displacement pump (7). In a preferred embodiment, as shown in FIG. 1, there are four vented housings on the extruder. Vacuum is generated via two vacuum pumps (8) and the vapours, which are distracted from the extruder are condensed in two condensers (9). Configurations with less but with at least one vented housing or with only one vacuum level applied are also according to the invention. The premixed and devolatized melt is transferred to a high viscosity reactor (2), which is also connected to a vacuum pump (8) and a condenser (9). After completion of the reaction the polysiloxane-polycarbonate block cocondensates are discharged from the high viscosity reactor via a discharge screw (3). The polymer strands are cooled in a waterhath (10) and cut in a granulator (11).

(2) FIG. 2 shows the wedge-shaped test bars used in the mechanical trials.

EXAMPLES

(3) The invention is described in detail hereinafter by working examples, the determination methods described here being employed for all corresponding parameters in the present invention, in the absence of any descriptions to the contrary.

(4) Determination of Melt Volume Flow Rate (MVR):

(5) The melt volume flow rate (MVR) is determined to ISO 1133 (at 300° C.; 1.2 kg), unless any other conditions have been described.

(6) Determination of Solution Viscosity (eta rel):

(7) The relative solution viscosity (η.sub.rel; also referred to as eta rel) was determined in dichloromethane at a concentration of 5 g/l at 25° C. with an Ubbelohde viscometer.

(8) Determination of Rearrangement Structures (Ia) to (IVa):

(9) The polycarbonate sample is hydrolysed by means of sodium methoxide under reflux. The corresponding solution is acidified and concentrated to dryness. The drying residue is dissolved in acetonitrile and the phenolic compounds of the formulae (Ia) to (IVa) are determined by means of HPLC with UV detection. The structures (Ia) to (IVa) are unambiguously characterized by means of nuclear magnetic resonance spectroscopy (NMR).

(10) Light Microscopy:

(11) The incorporation characteristics of the siloxane component are checked via light microscopy. The presence of large amounts (in the micrometer range or greater) of silicone oil is a pointer to physical incorporation of the silicone component. No block cocondensate is present. If, in contrast, the average size of the silicone domains is below 1 μm, the presence of a block copolymer can be assumed.

(12) Materials Used:

(13) PC: linear bisphenol A polycarbonate having end groups based on phenol from Bayer MatcrialScience used with a melt volume index of 59-62 cm.sup.3/10 min (measured at 300° C. and load 1.2 kg to ISO 1033). This polycarbonate does not contain any additives such as UV stabilizers, demoulding agents or thermal stabilizers. The polycarbonate was prepared via a melt transesterifieation process as described in DE 102008019503. The polycarbonate has a phenol end group content of about 600 ppm.

(14) Siloxane Component:

(15) Siloxane 1 is a hydroquinone-terminated polydimethylsiloxane of the formula (1) (i.e. R.sup.1=H, R.sup.2, R.sup.3=methyl, p=0), in which n=30 and m=3, having a hydroxy content of 8.8 mg KOH/g and a viscosity of 753 mPa.Math.s (23° C.). The weight-average molecular weight is Mw=13 000 g/mol, determined by means of gel permeation chromatography (GPC) with bisphenol A standard; detection was effected by means of an IR detector at 1050 cm.sup.−1.

(16) The siloxane component can be prepared according to the following procedure:

(17) In a reaction flask equipped with a thermostat heater, stirrer, thermometer, and reflux condenser, 250 g of an α,ω-bisacyloxypolydirnethylsiloxane, with an average chain length of 31.8 dimethylsiloxy units as determined by .sup.29Si NMR and 230 mmoles of acyloxy terminal groups, is added dropwise over 4 hours to a solution of 35.1 g (150 mmoles) bisphenol-A in 50 g xylenes, 25 g acetic acid and 0.5 g of sodium acetate, while heating to a mild reflux at 105° C. After complete addition the clear solution is stirred for an additional hour. Then the solvents and volatiles are removed by vacuum distillation to 160° C. and 3 mbar pressure. After cooling the crude product is filtered over a 3 micron filter (Seitz K300) to give 236 g (83% theory) of a clear, colorless liquid.

(18) Siloxanes 2 to 4 as described here below were prepared in an analogous manner.

(19) Siloxane 2 is a hydroquinone-terminated polydimethylsiloxane of the formula (1) (i.e. R.sup.1=H, R.sup.2, R.sup.3=methyl, p=0), in which n=31.4 and m=3.7, having a hydroxy content of 13.9 mg KOH/g and a viscosity of 307 mPa.Math.s (23° C.). The weight-average molecular weight is Mw=7 800 Wmol, determined by means of gel permeation chromatography (GPC) with bisphenol A standard; detection was effected by means of an IR detector at 1050 cm.sup.−1.

(20) Siloxane 3 is a hydroquinone-terminated polydimethylsiloxane of the formula (1) (i.e. R.sup.1=H, R.sup.2, R.sup.3=methyl, p=0), in which n=32 and m=3, having a hydroxy content of 12.5 mg KOH/g and a viscosity of 381 mPa.Math.s (23° C.). The weight-average molecular weight is Mw=9 380 g/mol, determined by means of gel permeation chromatography (GPC) with bisphenol A standard; detection was effected by means of an IR detector at 1050 cm.sup.31 1.

(21) Siloxane 4 is a hydroquinone-terminated polydimethylsiloxane of the formula (1) (i,e. R.sup.1=H, R.sup.2, R.sup.3=methyl, p=0), in which n=30 and m=3, having a hydroxy content of 14.9 mg KOH/g and a viscosity of 320 mPa.Math.s (23° C.). The weight-average molecular weight is Mw=9 100 g/mol, determined by means of gel permeation chromatography (GPC) with bisphenol A standard; detection was effected by means of an IR detector at 1050 cm.sup.−1.

(22) Catalyst:

(23) The catalyst used is tetrabenzylphosphonium phenoxide from Rhein Chemie Rheinau GmbH (Mannheim, Germany) in the form of a masterbatch. Tetraphenylphosphonium phenoxide is used in the form of a cocrystal with phenol and contains about 70% tetraphenylphosphonium phenoxide. The amounts which follow are based on the substance obtained from Rhein Chemie (as a cocrystal with phenol).

(24) The masterbatch is used in the form of a 0.25% mixture. For this purpose, 4982 g are subjected to spin application of 18 g of tetraphenylphosphonium phenoxide in a drum hoop mixer for 30 minutes. The masterbatch is metered in in a ratio of 1:10, such that the catalyst is present with a proportion of 0.025% by weight in the total amount of polycarbonate.

(25) Materials Used for Comparative Examples:

(26) Makrolon 2808®: Linear polycarbonate from Bayer MaterialScience based on bisphenol A with phenol as end group with an MVR of 9.5.

(27) Lexan® EXL 14141T: Linear siloxane-containing block cocondensate from Sabic Innovative Plastics based on bisphenol A with an MVR of 7.3, prepared by the via an interfacial process.

(28) Lexan EXL 9330: Linear siloxane-containing block cocondensate comprising flame retardant from Sabic Innovative Plastics based on bisphenol A with an MVR of 8.8, prepared via an interfacial process.

Comparative Examples

Twin-screw Extruder

(29) As a basis for comparison, experiments were first conducted according to the prior art with a single twin-screw extruder. The setup is thus similar to that as published in U.S. Pat. Nos. 5,414,054 and 5,821,321.

(30) For reactive extrusion, a twin-screw extruder (ZSE 27 MAXX from Leistritz Extrusionstechnik GmbH, Nuremberg) is used. The extruder consists of 11 housing parts—see FIG. 1. In housing part 1 polycarbonate and catalyst masterbatch are added, and in housing 2 and 3 these components are melted. In housing part 4 the liquid silicone component is added. Housing parts 5 and 6 serve for incorporation of the silicone component. Housings 7 to 10 are provided with venting orifices in order to remove the condensation products. Housings 7 and 8 are assigned to the first vacuum stage, and housings 9 and 10 to the second. The reduced pressure in the first vacuum stage is between 250 and 500 mbar absolute pressure. The reduced pressure in the second vacuum stage can be found in Table 1. is less than 1 mbar. In zone 11, finally, the pressure buildup is effected, and then the discharge from the extruder with subsequent pelletization. Several experimental batches were run. In these, several process parameters such as speed, housing temperature and pressure in vacuum zone 2 were varied.

(31) TABLE-US-00001 TABLE 1 Cat. Housing Visc. Incorporation PC MB Cat. Siloxane.sup.1) Speed Vacuum 2 temp. eta (light Ex. kg/h kg/h % kg/h rpm mbar abs. ° C. rel. microscopy) 1 13.5 1.5 0.25 0.75 100 Standard 330 1.198 no pressure 2 13.5 1.5 0.25 0.75 400 Standard 330 1.198 no pressure 3 13.5 1.5 0.25 0.75 100 Standard 350 1.197 no pressure 4 13.5 1.5 0.25 0.75 400 Standard 350 1.197 no pressure 5 13.5 1.5 0.25 0.75 100 6-8 mbar 330 1.199 no 6 13.5 1.5 0.25 0.75 400 15 330 1.200 no 7 13.5 1.5 0.25 0.75 100  3 350 1.199 no 8 13.5 1.5 0.25 0.75 400  3 350 1.199 no .sup.1)In Examples 1-8 siloxane 1 was used.

(32) Comparative Examples 1-8 show condensation to give a higher molecular weight material is achievable neither under standard pressure nor under fine vacuum. The solution viscosity remains unchanged compared to the starting material within the accuracy of measurement. The variation of the speed and hence of the shear energy introduced, and of the housing temperature, does not result in a change in the viscosity either. Light microscopy analysis shows that the silicone component is merely physically incorporated in the extruded material. This was surprising, since the incorporation of the silicone component was possible in U.S. Pat. Nos. 5,414,054 and 5,821,321. However, the silicone component introduced here, in combination with the catalyst, is probably unsuitable for preparation of a copolymer.

(33) TABLE-US-00002 TABLE 2 Inventive Examples (use of a reactor combination of a twin-screw extruder and a high-viscosity reactor) Cat. Housing Incorporation PC MB Cat. Siloxane.sup.2) Speed temperature (light Ex. kg/h kg/h % kg/h rpm Vacuum ° C. Viscosity. microscopy)  9.sup.1) 13.5 1.5 0.25 0.75 200 200 mbar 350 (TSE) 1.294 yes (TSE Z2) 350 (HVR) 0.9 mbar (HVR) 10 13.5 1.5 0.25 0.75 400 120 mbar 350 (TSE) 1.282 yes (TSE Z2) 350 (HVR) 0.5 mbar (HVR) 11 13.5 1.5 0.25 0.75 300 200 mbar 350 (TSE) 1.337 yes (TSE Z2) 350 (HVR) 0.8 mbar (HVR) .sup.1)Concentraion of the rearrangement structures contained in the cocondensate: (Ia) 65 ppm, (IIa) 51 ppm, (IIIa) 14 ppm and (IVa) 23 ppm, based on teh cocondensate and determined after hydrolysis. .sup.2)In example 9, siloxane 2 was used. In example 10, siloxane 3 was used and in example 11, siloxane 4 was employed.

(34) Inventive Examples 9-11 show that a high molecular weight product can be achieved in the inventive machine configuration. The solution viscosities of the products which have been obtained via a reactive extrusion are within the range from high-viscosity injection moulding or extrusion types.

(35) It was shown by light microscopy images that a homogeneous distribution of the silicone domains is present.

(36) The shear viscosities of the block cocondensate obtained by the process according to the invention and of conventional commercially available siloxane-containing block cocondensates and conventional linear polycarbonates based on bisphenol A are shown in Table 3.

(37) TABLE-US-00003 TABLE 3 Shear viscosities at various shear rates at 300° C. (high-pressure capillary rheometer) Makrolon ® 2808 Lexan ® EXL1414T Lexan ® EXL9330 Example 9 Example 10 (Comparative (Comparative (Comparative (Inventive (Inventive Shear example) example) example) example) example) rate viscosity viscosity viscosity viscosity viscosity [s.sup.−1] [Pas] [Pas] [Pas] [Pas] [Pas] 50  570* 525 484 547 451 100 554 479 437 484 407 200 532 417 387 397 336 500 456 332 315 270 232 1000 363 258 243 201 165 1500 302 216 202 169 138 *value at 50 s.sup.−1 extrapolated

(38) It is apparent from Table 3 that the viscosity decreases significantly at relatively high shear rates in the inventive examples. For example, in the case of linear polycarbonate (Makrolon® 2808), the viscosity, with comparable zero viscosity is higher under high shear rates than in the case of the inventive examples. Surprisingly, the flowability, with similar or even higher starting viscosity, for the inventive materials is thus higher under shear compared to conventional, commercially available siloxane block copolycarbonates obtained in the interfacial process. This was surprising and unforeseeable.

(39) TABLE-US-00004 TABLE 4 Melt stability (MVR 300° C. after residence times) Makrolon 2808 Lexan EXL1414T Lexan EXL9330 Example 9 Example 10 Residence (Comparative (Comparative (Comparative (Inventive (Inventive time example) example) example) example) example) [min] MVR MVR MVR MVR MVR  4 9.76 7.28 8.75 8.11 10.39 20 9.77 7.04 10.61 8.10 10.37 30 9.84 8.35 11.0 7.90 10.29 Δ (4/30 min) 0.08 1.07 2.25 0.21 0.1

(40) Surprisingly, the inventive samples (Examples 9 and 10), in spite of production in a reactive extrusion process, exhibit a high melt stability. The melt stability is surprisingly even higher than in the case of siloxane-containing polycarbonates which have been obtained in the interfacial process.

(41) Mechanical Behavior at Different Wall Thickness:

(42) For the mechanical trials test bars with a wedge-shaped geometry were prepared by injection molding.

(43) V-notches were applied on the wedge shaped samples at different positions (different thicknesses). The samples had V-shaped notches with a notch radius of 0.10 mm and 0.25 mm at different thicknesses.

(44) A three point bending test was performed at each sample at room temperature.

(45) The trials were performed on an Instron 5566 testing machine with a strain rate of 10 mm/min with 42 mm distance between the support edges (see FIG. 2).

(46) TABLE-US-00005 TABLE 5 Makrolon 2808 (Comparative Example 9 example) (inventive example) Critical thickness (0.10 mm) 5.65 ± 0.05 mm >7.0 mm Critical thickness (0.25 mm) 6.75 ± 0.25 mm >7.0 mm

(47) It could be shown that the critical thickness is higher for the material according to the invention when compared to a standard polycarbonate material. The standard polycarbonate sample shows a critical thickness of 5.65 mm for a notch radius of 0.1 mm whereas the inventive material is still ductile at this thickness (critical thickness higher than 7.0 mm).

(48) Effect of the Addition of Sodium Acetate:

(49) The reactive extrusion was carried out similar to the examples described above. Deviating from the examples above, a siloxane with a sodium content of 1.3 ppm in the form of sodium acetate was used. The extrusion data set is shown below.

(50) TABLE-US-00006 TABLE 6 Cat. Housing PC MB Cat. Siloxane Speed temperature Visc. Ex. kg/h kg/h % kg/h rpm Vacuum ° C. eta rel. 12 27 3 0.25 1.5 600 350 mbar (ZSK Z2) 350 (ZSK) 1.288 1.1 mbar (HVR) 350 (HVR)

(51) The reactive extrusion was carried out similar to the examples described above. Deviating from the examples above, a siloxane with a sodium content of 2.5 ppm in the form of sodium benzoate was used. The extrusion data set is shown below.

(52) TABLE-US-00007 TABLE 7 Cat. Housing PC MB Cat. Siloxane Speed temperature Visc. Ex. kg/h kg/h % kg/h rpm Vacuum ° C. eta rel. 13 45 5 0.25 2.5 680 180 mbar (ZSK Z2) 350 (ZSK) not 1.0 mbar (HVR) 350 (HVR) determined

(53) Thus, it could be shown that by using special co-catalysts the throughput on the reactor could be enhanced considerably.

(54) It becomes evident from table 8 that despite the use of alkaline substances and although no quencher or stabilizer was used, the resulting block cocondensate shows high melt stability.

(55) TABLE-US-00008 TABLE 8 MVR according to ISO 1133 after different residence times (300° C; 1.2 kg) Example 12 Example 13 MVR 5 min 8.3 9.0 20 min 8.4 9.1 30 min 8.3 9.2