Branched polycarbonates containing hydroxy-naphthoic acids or their derivatives, and process for preparing them

Abstract: Branched, thermoplastic polycarbonates, suitable for being processed according to the blow-molding technique, are prepared by copolymerization with hydroxy-naphthoic acids or their derivatives.

Description: The present invention relates to branched, thermoplastic carbonates, suitable for fabrication by blow-molding (blow molding of hollow bodies). Linear polycarbonates have been long known in the art. Such polymers are largely used in many application sectors but, contrarily to most thermoplastic polymers, they are not suitable for being processed by extrusion or by the blow-molding technique, which are the suitable techniques for manufacturing particular fabricated products (alveolar sheets, bottles, hollow containers, and so forth). This difficulty of processability of linear polycarbonate is due to its exclusively Newtonian behaviour, according to which the apparent viscosisty (η) is substantially independent from the shear rate (γ ˙). On the contrary, the fabrication of a material according to the extrusion or blow-molding techniques requires that it has a decreasing apparent viscosity with increasing shear rates, a typical feature of non-Newtonian behaviour, so that two successive statuses can be differentiated in the molten polymer: a first status, when the polymer is inside the processing machine (e.g., an extruder), and the other one when the product exits it (e.g., through the die of the same extruder). During the first step, the shear rates the fluid is submitted to are high and its apparent viscosity is low, so that the processability of said molten polymer results easier; when the polymer leaves the extruder, on the contrary, low values of γ ˙ and high viscosity values are obtained, which prevent the product from collapsing, and enable the manufactured item to be endowed with a good dimensional stability. The non-Newtonian behaviour of the molten polymer has a considerable influence on two properties thereof, viz., the melt elasticity and the melt strength, which are very important as well for the purposes of the extrusion and blow-molding processing techniques. The melt elasticity substantially consists in the capability shown by a non-Newtonian fluid, of swelling, when exiting a die, to a greater extent than a Newtonian fluid, as a consequence of a higher recovery of elastic energy inside the interior of its mass, thanks to a greater molecular distorsion and orientation under the action of a shear stress. All the above phenomena result in an increase in product processability, owing to a higher flexibility and ductility of the material. Vice-versa, the second above-indicated property, the melt strength, becomes meaningful when the molten material exits the fabrication machine. Said melt strength can be regarded as the tenacity of the polymer in the molten state, i.e., the capability exhibited by this latter to withstand stresses. If, in fact, the molten mass does not succeed in supporting its own weight, the extrudate collapses and, as a consequence, the desired shapes cannot be obtained in the manufactured articles. It results evident from the above that the polymers with a non-Newtonian behaviour exhibit two basic characteristics, which make them suitable for being fabricated by extrusion and/or blow-moulding: a great easiness of machine processing (a low apparent viscosity for high values of γ ˙ and a high melt elasticity) and a very good dimensional stability when leaving the machine (a high melt viscosity for low values of γ ˙ and a considerably high melt strength). From the prior art, branched polycarbonates are known, which are endowed with non-Newtonian rheologic properties, and are suitable for being fabricated by extrusion and blow-moulding. Such polycarbonates can be obtained by copolymerization with polyfunctional comonomers containing three or more -OH and/or -COOH and/or -COCl groups: exemplary of the prior art are US-A-4 562 242 and DE-OS-15 95 762. The main technical problem to be coped with when branched polycarbonates are prepared, essentially derive from the poor reactivity of the polyfunctional comonomer used, due to the fact that not all functional groups react to a complete, or practically complete, extent. Therefore, the so-obtained polycarbonates display a lower branching degree than desired, and their preparation requires a large comonomer consumption. The present Applicants have now found that the drawbacks of the prior art can be overcome, if a comonomer is used, which has three or more functional groups, all of which react to a complete, or practically complete extent under the conditions of use. The branched polycarbonates obtained by using such a comonomer show a shear sensitivity (which is the ratio between the melt-flow rate values at two different shear rates) of more than 15, while simultaneously retaining the other characteristics typical of the linear polycarbonates. This invention, therefore, provides blow-mouldable branched polycarbonates produced from an aromatic dihydroxy compound having the formula: wherein: R, if present, is a substituted- or unsubstituted alkyl containing up to 5 carbon atoms, or is -O-, -S-, -SO₂-, or -CO-; X and Y, equal to, or different from one another, are -H,-CH₃ or a halogen atom, and m and n , equal to, or different from one another, are 1, 2, 3, or 4, phosgene, and a compound having the formula: wherein: Z is -OH or -Cl, R₁ is -OH; R₃ and R₄, equal to, or different from, one another are -OH, -H, or a C₁-C₄ alkyl; R and R₂ are -H or a C₁-C₄ alkyl, and at least two of the substituents are -OH. The invention also contemplates a process for preparing the blow-mouldable branched polycarbonates referred to above comprising the steps of: (a) Preparing a chloroformyl-terminated oligomer by reacting phosgene with a compound of formula (II); (b) Condensing the oligomer thus obtained with a compound of formula (I), and polycondensation (c) Recovering the thus produced blow-mouldable branched polycarbonate from the reaction mixture. According to this invention, the chloroformyl-terminated oligomers are prepared by interface reaction between phosgene and a compound of formula (II) dissolved in an aqueous alkaline solution, in the presence of a water-immiscible organic solvent and of a molecular weight regulators, such as, e.g., p.tert.butylphenol or p.isopropylphenol. Exemplary of the compounds of formula (II) which can be used, are: 4,4'-dihydroxy-biphenyl; 2,2-bis-(4-hydroxyphenyl)-propane (Bisphenol A); 2,2-bis-(3,5-dichloro-4-hydroxyphenyl)-propane; 2,2-bis-(3,5-dimethyl-4-hydroxyphenyl)-propane, and bis-(4-hydroxyphenyl)-methane. Also bivalent compounds with one aromatic ring only, such as resorcinol or hydroquinone, can be used. The reaction is carried out at a temperature comprised within the range of from 15°C to 35°C, and preferably at room temperature (20-25°C). The so-obtained oligomers have a molecular weight comprised within the range of from 400 to 2,000. After the phase separation, to the organic phase containing the chloroformyl-terminated oligomers, the solution of the polyfunctional comonomer (I) in an organic solvent immiscible with water is added, with the amount of comonomer being such as to make it possible an end polycarbonate containing at least 0.01 mol of comonomer, and preferably from 0.1 to 2.0 mol of comonomer per each 100 mol of aromatic dihydroxy-compound (II) to be obtained. Organic solvents immiscible with water are selected from those known from the prior art, and methylene chloride is preferably used. Some examples of polyfunctional comonomers used are: 3,5-dihydroxy-2-naphthoic acid; 3,7-dihydroxy-2-naphthoic acid; 3,5-dihydroxy-2-chlorocarbonyl-naphthalene; 3,7-dihydroxy-2-chlorocarbonyl-naphthalene; Said comonomers can be obtained according to processes known in the art, and most of them can be easily found on the market. If the commercial products are used, they have to be carefully purified before being used according to the purposes of the present invention. After the addition of the solution containing the comonomer (I), the reaction is continued by adding an aqueous-alkaline solution containing a reducing agent, preferably sodium dithionite, in order to prevent coloured by-products from forming, and then an aqueous solution is added, which contains the phase-transfer catalyst, e.g., a tertiary amine, preferably triethylamine. The temperature at which the condensation is carried out is comprised within the range of from 15°C to 35°C, and is preferably kept at values around room temperature (20-25°C). After a time period ranging from 30 to 60 minutes, and preferably of 40 minutes, the biphasic system deriving from the condensation with the polyfunctional comonomer is treated with an alkaline solution of the aromatic dihydroxy-derivative. An aqueous-alkaline solution of sodium hydroxide at 20% by weight is then added. After a time of from 2 to 3 hours, the so-obtained branched polycarbonate is isolated by washing the organic phase according to the methods known in the art, and distillation of the solvent, or precipitation with a non-solvent. The preparation of such branched polycarbonates can be also carried out according to other processes, such as, e.g., the process according to which aromatic dihydroxy-derivatives, phosgene and the polyfunctional comonomer are condensed by means of an interface reaction, or in solution, by means of a single-step reaction. Such polycarbonates can be also obtained by transesterification in the molten state, with the dihydroxy-aromatic compound being reacted with diaryl-, dialkyl- or alkylaryl-carbonates at temperatures comprised within the range of from 100 to 300°C, in the presence of transesterification catalysts. The branched polycarbonates of the present invention have a molecular weight comprised within the range of from 20,000 to 30,000, and are characterized in that they are completely soluble in the usual solvents for linear polycarbonate, and in that their melt-viscosity is strongly depending on the shear rate. Such branched polycarbonates are therefore suitable for being processed both by the injection-moulding technique, and for example by extrusion. Owing to the excellent stability of their molten mass, such polycarbonates are particularly suitable for being fabricated by means of the blow-molding method, in order to produce hollow bodies. The reactivity of the polyfunctional comonomer used as the branching agent is such that amounts of at least 0.01 mol, and preferably comprised within the range of from 0.1 to 2.0 mol of such comonomer per each 100 mol of aromatic dihydroxy-compound are enough for reaching such a crosslinking degree, that the shear-sensitivity has always values higher than 15. In order to characterize the branched polycarbonates according to the present invention, the following methods were used: Intrinsic viscosity - Is determined in methylene chloride at 20°C by means of the Ubbelhode viscometer, and is expressed as dl/g. Shear sensitivity - The evaluation of this quantity is carried out by using the melt indexer, under loads of 2.16 and 21.6 kg at 260°C, according to ASTM D 1238. Impact strength (IZOD) - Is evaluated on notched specimens at 0°C, according to ASTM D 256. The following examples are illustrative, and non-limitative of the same invention. Example 1 Purification of 3,7-dihydroxy-2-naphthoic acid 3.5 g of commercial 3,7-dihydroxy-2-naphthoic acid (purity level = 86%, computed by indirect acidimetric titration) is dissolved in 40 ml of an aqueous solution of Na₂S₂O₄ at 0.1% by weight. To such solution, beforehand 1.4 g of Na₂CO₃ and then 20 ml of methyl-isobutyl-ketone are added, under a nitrogen stream, and with mechanical stirring. The so-obtained mixture is then heated at 40°C for a 3-hour time. At the end of this time period, the mixture is allowed to return back to room temperature (20-25°C), and the aqueous phase is separated and is then acidified with H₂SO₄ at 30% by weight, until a pH value = 2 is reached. The precipitated product is filtered off, the filter panel is washed many times with water portions of 500 ml, and is finally dried under vacuum. The obtained product is dissolved again in an aqueous solution of Na₂S₂O₄ at 0.1%, and is treated again as previously disclosed. The end product obtained is a 3,7-dihydroxy-2-naphthoic acid having a purity level equal to, or higher than, 99%. The elemental analysis thereof supplies the following data: C = 59.5% (theoretical: 59.4%); H = 3.3% (theoretical: 3.2%). Example 2 To a glass reactor of 3 litres of capacity, maintained at the controlled temperature of 25°C, under nitrogen 84 g of bisphenol A, 300 mg of 3,7-dihydroxy-2-naphthoic acid (equivalent to 0.4 mol % relatively to bisphenol A), 65.2 g of sodium hydroxide dissolved in 650 ml of water, 20 mg of sodium dithionite (as a reducing agent) and 6.3 ml of a 0.5 N aqueous solution of trimethylamine are charged. 2.7 g of p-tert.-butylphenol dissolved in 1,300 ml of methylene chloride is then added, and into the mixture, maintained with vigorous stirring, 44 g of phosgene gas is bubbled over 30 minutes. The reaction is let proceed for 2 hours, with aqueous sodium hydroxide at 20% by weight being added, in order to keep pH value higher than 11. At the end, the reaction mixture is diluted with 500 ml of methylene chloride, and the organic phase is separated and washed, in the order, with 300 ml of water (twice), 800 ml of 0.15 N aqueous sodium hydroxide (three times), 600 ml of water (twice), 800 ml of 0.1 N hydrochloric acid, and finally with portions of 600 ml of water until neutral. At the end, the polymer is recovered by distilling off the organic solvent, is dried and ground until a powder is obtained. The branched polycarbonate obtained shows the following characteristics: Intrinsic viscosity = 0.510 dl/g; Shear sensitivity = 21.2 IZOD impact strength = 771 J/m Example 3 The process is carried out with the same operating modalities as of Example 2, except for that instead of 3,7-dihydroxy-2-naphthoic acid, 300 mg of 3,5-dihydroxy-2-naphthoic acid (0.4 mol % relatively to total bisphenol A) is used. The branched polycarbonate obtained has the following characteristics: intrinsic viscosity = 0.512 dl/g shear sensitivity = 23.3 IZOD impact resistance = 802 J/m Example 4 226 g of chloroformyl-terminated polycarbonate oligomers (number average molecular weight = 722; chloroformyl end groups = 2,611 meq/kg; hydroxy end groups = 160 meq/kg), prepared from bisphenol-A, phosgene and p-tert.-butylphenol, is dissolved in 900 ml of methylene chloride containing 3.53 g of 3,7-dihydroxy-2-chlorocarbonyl-naphthalene (1.55 mol % relatively to total bisphenol A), and is charged, under nitrogen stream, to a glass reactor of 2.5 litres of capacity, maintained at the controlled temperature of 25°C. While the above solution is maintained with mechanical stirring by means of a double-anchor stirrer (300 rpm), to it a solution of 350 ml of water containing 52.1 g of bisphenol A, 21.5 g of sodium hydroxide, 31 mg of sodium dithionite, and 5 ml of an 0.05 N aqueous solution of triethylamine are added in the same order as stated. Subsequently, 92 ml of an aqueous solution of sodium hydroxide at 20% by weight is charged over 10 minutes, by means of a metering pump. After 3 hours, the mixture is poured into 2,200 ml of methylene chloride; the organic phase is then separated and washed, in the same order as stated, with 450 ml of water (twice), 1,300 ml of 0.15 N aqueous sodium hydroxide (three times), 900 ml of water (twice), 1,300 ml of 0.1 N hydrochloric acid and, finally, with portions of 900 ml of water up to neutral pH value. The branched polycarbonate, isolated by means of the usual methodology, shows the following characteristics: intrinsic viscosity = 0.499 dl/g; shear sensitivity = 20.3 IZOD impact strength = 725 J/m Example 5 226 g of chloroformyl-terminated polycarbonate oligomers (number average molecular weight = 722; chloroformyl end groups = 2,611 meq/kg; hydroxy end groups = 160 meq/kg), prepared from bisphenol-A, phosgene and p-tert.-butylphenol, is dissolved in 900 ml of methylene chloride and is charged, under nitrogen, to a glass reactor of 2.5 litres of capacity, kept at the controlled temperature of 25°C. While the above solution is maintained with mechanical stirring by means of a double-anchor stirrer (300 rpm), to it 50 ml of water containing 810 mg of 3,7-dihydroxy-2-naphthoic acid (0.38 mol % relatively to total bisphenol A), 1.8 g of sodium hydroxide, 31 mg of sodium dithionite, and 5 ml of a 0.05 N aqueous solution of triethylamine are added in the same order as stated. 40 minutes later, 300 ml of water containing 55.8 g of bisphenol A and 19.7 g of sodium hydroxide and, then, over 10 minutes, 92 ml of an aqueous solution of sodium hydroxide at 20% by weight are charged by means of a metering pump. After 3 hours, the mixture is poured into 2,200 ml of methylene chloride; the organic phase is then separated and washed, in the same order as stated, with 450 ml of water (twice), 1,300 ml of 0.15 N aqueous sodium hydroxide (three times), 900 ml of water (twice), 1,300 ml of 0.1 N hydrochloric acid and, finally, with portions of 900 ml of water up to neutral pH value. The branched polycarbonate, isolated by means of the usual methodology, shows the following characteristics: intrinsic viscosity = 0.487 dl/g; shear sensitivity = 18.0 IZOD impact strength = 735 J/m Example 6 The process is carried out with the same operating modalities and amounts of reactants as of Example 5, except for that 1.62 g of 3,7-dihydroxy-2-naphthoic acid (0.77 mol % relatively to total bisphenol A) is used. The branched polycarbonate obtained has the following characteristics: intrinsic viscosity = 0.538 dl/g shear sensitivity = 22.2 IZOD impact resistance = 790 J/m Example 7 The process is carried out with the same operating modalities and amounts of reactants as of Example 5, except for that the amount of 3,7-dihydroxy-2-naphthoic acid used is of 2.43 g (1.13 mol % relatively to total bisphenol A). The branched polycarbonate obtained has the following characteristics: intrinsic viscosity = 0.589 dl/g shear sensitivity = 27.5 IZOD impact resistance = 810 J/m Example 8 (comparative example) The process is carried out with the same operating modalities and amounts of reactants as of Example 5, except for that instead of 3,7-dihydroxy-2-naphthoic acid, 740 mg of 1,4-dihydroxy-2-naphthoic acid (0.35 mol % relatively to total bisphenol A) is used. The branched polycarbonate obtained has the following characteristics: intrinsic viscosity = 0.474 dl/g shear sensitivity = 16.8 IZOD impact resistance = 757 J/m Example 9 (comparative example) The process is carried out with the same operating modalities and amounts of reactants as of Example 5, except for that instead of 3,7-dihydroxy-2-naphthoic acid, 1.49 g of 1,4-dihydroxy-2-naphthoic acid (0.71 mol % relatively to total bisphenol A) is used. The branched polycarbonate obtained has the following characteristics: intrinsic viscosity = 0.509 dl/g shear sensitivity = 18.1 IZOD impact resistance = 780 J/m Example 10 The process is carried out with the same working conditions and amounts of reactants as in Example 5, with the exception that the 3,7-dihydroxy-2-naphthoic acid is replaced by 750 mg of 3,5-dihydroxy-2-naphthoic acid (0,35 mol% relative to the total bisphenol A). The branched polycarbonate obtained has the following characteristics: intrinsic viscosity = 0.496 dl/g shear sensitivity = 20.2 IZOD impact resistance = 794 J/m Example 11 The process is carried out with the same working conditions and amounts of reactants as of Example 5, except for that instead of 3,7-dihydroxy-2-naphthoic acid, 1.51 g of 3,5-dihydroxy-2-naphthoic acid (0.72 mol % relatively to total bisphenol A) is used. The branched polycarbonate obtained has the following characteristics: intrinsic viscosity = 0.523 dl/g shear sensitivity = 25.3 IZOD impact resistance = 807 J/m

Claims: Claims for the following Contracting States : AT, BE, CH, DE, FR, GB, GR, LI, LU, NL, SE, Blow-mouldable branched polycarbonates produced from an aromatic dihydroxy compound having the formula: wherein: R, if present, is a substituted- or unsubstituted alkyl containing up to 5 carbon atoms, or is -O-, -S-, -SO₂-, or -CO-; X and Y, equal to, or different from one another, are -H,-CH₃ or a halogen atom, and m and n , equal to, or different from one another, are 1, 2, 3, or 4, phosgene, and a compound having the formula: wherein: Z is -OH or -Cl, R₁ is -OH; R₃ and R₄, equal to, or different from, one another are -OH, -H, or a C₁-C₄ alkyl; R and R₂ are -H or a C₁-C₄ alkyl, and at least two of the substituents are -OH. Blow-mouldable branched polycarbonates according to Claim 1, wherein the compound of formula (I) is selected from: 3,5-hydroxy-2-naphthoic acid; 3,7-hydroxy-2-naphthoic acid; 3,5-dihydroxy-2-chlorocarbonyl-napthalene, and 3,7-dihydroxy-2-chlorocarbonyl-napthalene. Blow-mouldable branched polycarbonates according to Claim 1, wherein the compound of formula (I) is present in an amount of at least 0,01 mol per hundred mol of the compound of formula (II). Blow-mouldable branched polycarbonates according to Claim 3, wherein the compound of formula (I) is present in an amount of from 0,1 to 0,2 mol per hundred mol of the compound of formula (11). Process for preparing the blow-mouldable branched polycarbonates defined in claim 1, comprising the steps of: (a) Preparing a chloroformyl-terminated oligomer by reacting phosgene with a compound of formula (II); (b) Condensing the oligomer thus obtained with a compound of formula (I), and polycondensation (c) Recovering the thus produced blow-mouldable branched polycarbonate from the reaction mixture. Process according to Claim 5, wherein the compound of formula (II) used in step (a) is selected from: 4,4'-dihydroxy-biphenyl; 2,2-bis-(4-hydroxyphenyl)-propane; 2,2-bis-(3,5-dichloro-4-hydroxyphenyl)-propane; 2,2-bis-(3,5-dimethyl-4-hydroxyphenyl)-propane, and bis-(4-hydroxyphenyl)-methane. Process according to Claim 5, wherein step (a) is carried out in a biphasic water/organic solvent medium in the presence of a monofunctional phenol as the molecular-weight regulator, the oligomers thus obtained having a molecular weight of from 400 to 2.000. Process according to Claim 7, wherein the molecular-weight regulating monofunctional phenol is selected from phenol, p.isopopropyl-phenol, and p.tert.butyl-phenol, the organic solvent being methylene chloride. Process according to Claim 5, wherein step (b) is carried out in the presence of a phase-transfer catalyst, the compound of formula (I) being selected from: 3,5-hydroxy-2-naphthoic acid; 3,7-hydroxy-2-naphthoic acid; 3,5-dihydroxy-2-chlorocarbonyl-napthalene, and 3,7-dihydroxy-2-chlorocarbonyl-napthalene. Process according to Claim 9, wherein, in step (b), the organic solvent is methylene chloride and the phase-transfer-catalyst is a tertiary amine. Claims for the following Contracting State : ES Process for preparing blow-mouldable branched polycarbonates produced from an aromatic dihydroxy compound having the formula: wherein: R, if present, is a substituted- or unsubstituted alkyl containing up to 5 carbon atoms, or is -O-, -S-, -SO₂-, or -CO-; X and Y, equal to, or different from one another, are -H,-CH3 or a halogen atom, and m and n , equal to, or different from one another, are 1, 2, 3, or 4, phosgene, and a compound having the formula: wherein: Z is -OH or -Cl, R₁ is -OH; R₃ and R₄, equal to, or different from, one another are -OH, -H, or a C₁-C₄ alkyl; R and R₂ are -H or a C₁-C₄ alkyl, and at least two of the substituents are -OH, characterized by comprising the steps of: (a) Preparing a chloroformyl-terminated oligomer by reacting phosgene with a compound of formula (II); (b) Condensing the oligomer thus obtained with a compound of formula (I), and polycondensation (c) Recovering the thus produced blow-mouldable branched polycarbonate from the reaction mixture. Process according to Claim 1 , characterized in that the compound of formula (I) is selected from: 3,5-hydroxy-2-naphthoic acid; 3,7-hydroxy-2-naphthoic acid; 3,5-dihydroxy-2-chlorocarbonyl-napthalene, and 3,7-dihydroxy-2-chlorocarbonyl-napthalene. Process according to Claim 1 , characterized in that the compound of formula (II) used in step (a) is selected from: 4,4'-dihydroxy-biphenyl; 2,2-bis-(4-hydroxyphenyl)-propane; 2,2-bis-(3,5-dichloro-4-hydroxyphenyl)-propane; 2,2-bis-(3,5-dimethyl-4-hydroxyphenyl)-propane, and bis-(4-hydroxyphenyl)-methane. Process according to Claim 1, characterized in that step (a) is carried out in a biphasic water/organic solvent medium in the presence of a monofunctional phenol as the molecular-weight regulator, the oligomers thus obtained having a molecular weight of from 400 to 2.000. Process according to Claim 4 , characterized in that the molecular-weight regulating monofunctional phenol is selected from phenol, p.isopopropyl-phenol, and p.tert.butyl-phenol, the organic solvent being methylene chloride. Process according to Claim 1 ,characterized in that step (b) is carried out in the presence of a phase-transfer catalyst, the compound of formula (I) being selected from: 3,5-hydroxy-2-naphthoic acid; 3,7-hydroxy-2-naphthoic acid; 3,5-dihydroxy-2-chlorocarbonyl-napthalene, and 3,7-dihydroxy-2-chlorocarbonyl-napthalene. Process according to Claim 6, wherein, in step (b), the organic solvent is methylene chloride and the phase-transfer-catalyst is a tertiary amine.

Inventors: PETRI ALBERTO, PETRI, ALBERTO
Applicants: ENICHEM SPA, ENICHEM S.P.A.
Application year: 1988
Main classification: C08G63
IPC codes: C08G63, C08G64