MXPA00009119A - Polyalkylene arylates containing a high proportion of carboxyl end groups - Google Patents

Abstract

According to the inventive method for producing polyalkylene arylates, an aromatic dicarboxylic acid or its esters or ester-forming derivatives is/are esterified or transesterified with a molar excess of an aliphatic dihydroxy compound and the resulting transesterification or esterification product is polycondensed. The invention is characterised in that the prepolymer is polycondensed with a viscosity number (VZ) of<30 ml/g in the presence of an oxygen-containing gas.

Description

POULTRY ARTHIES WITH HIGH CONTENT OF CARBOXYL GROUPS TERMINALS The invention relates to an improved process for preparing polyalkylene arylates having a high carboxyl terminal group content. The invention also relates to the polyalkylene arylates that can be obtained by the novel process, and also to mixtures thereof with polycarbonates and / or polyamides, and to the use of such molding compositions to produce parts molded, and the resulting molded parts. Processes for preparing polyesters are known, inter alia, from DE-A 25 14 116, EP-A 815 158 and GB-A 2 184 129. Initial materials, such as diols and acids and / or esters thereof, they are generally esterified or transesterified in the presence of catalysts, followed by one or more polycondensation steps under reduced or modified pressure. The polyesters obtained from most of the known processes have low content of carboxyl end groups. For example, polybutylene terephthalate has very low moisture absorption and high dimensional stability, along with good resistance to solvents. However, a disadvantage is its limited stiffness, for example, compared to polycarbonates or polyamides. The mixtures of these polymers with PBT have the combination of properties desired for different applications, where a particular value is put on the good mechanical properties such as, for example, high rigidity. In the prior art, high molecular weight polyester blends are prepared by a complicated composition process, where the polyester is maintained above the melting point during extended dwell times and has to be mixed in this phase with the other components of mix. At this point, a very important factor is the proper mixing of the components of the mixture. The formation of the block copolymers, using reactive groups on the matrix of the polypropylene, can improve the compatibility of the phases. When preparing a polyester mixture of this type, care must also be taken that the chemical properties of a polymer do not cause degradation of the other components of the mixture. In the prior art, polyester blends are prepared by mixing the polymers using kneading machinery (single or double axis, co- or counter-rotating, interleaving design or non-intercalation). This additional process step causes thermal degradation of the polymer during melting and mixing. To prepare a mixture it would be desirable to use a polyester having a very high content of carboxyl terminal groups, thus favoring compatibilization through reactive coupling and substantially avoiding degradation of the other components of the mixture. An object of the present invention is to provide a cost-effective process for obtaining polyalkylene arylates with a very high content of terminal carboxyl groups. We have found that this objective is achieved by means of a process for preparing polyalkylene arylates by esterification or transesterification of aromatic dicarboxylic acid or its esters or ester-forming derivatives with a molar excess of an aliphatic dihydroxy compound and the polycondensation of the product of the esterification or resulting transesterification, which consists in polymerizing the polymer with a viscosity index (IV) of < 30 ml / g in the presence of a gas containing oxygen. Preferred modalities are given in the sub-clauses. We have also found that the polyalkylene arylates that can be obtained by the novel process, when combined with polycarbonates and / or with polyamides, provide better phase compatibility and therefore better mechanical properties. In addition, the molecular weight of the other components of the mixture does not deteriorate very substantially during the preparation. Polyalkylene arylates are known per se and are described in the literature. Its main chain contains an aromatic ring that comes from aromatic dicarboxylic acid. The aromatic ring can also be substituted, for example, by halogen, such as chlorine and bromine, or by C 1 -C 4 alkyl, such as methyl, ethyl, isopropyl, n-propyl, n-butyl, isobutyl or tert-butyl. The preferred dicarboxylic acids that may be mentioned are 2,6-naphthalene dicarboxylic acid and terephthalic acid, and mixtures thereof. Up to 30 mol%, preferably no more than 10 mol% of the aromatic dicarboxylic acids can be substituted by aliphatic or cycloaliphatic dicarboxylic acids, such as adipic acid, azelaic acid, sebacic acid, dodecandioic acids and cyclohexanedicarboxylic acids. Among the aliphatic dihydroxy compounds preference is given to diols having from 2 to 6 carbon atoms, in particular 1,2-ethanediol, 1,3-propanediol, 1,4-butanediol, 1,6-hexanediol, 1, 4-hexanediol, 5-methyl-l, 5-pentanediol, 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol and neopentyl glycol, and mixtures thereof.

Particularly preferred polyesters (a) which may be mentioned are polyalkylene terephthalates which are obtained from alkanediols having from 2 to 10 carbon atoms, preferably from 2 to 6 carbon atoms. Among these, particular preference is given to polyethylene terephthalate and polybutylene terephthalate, and mixtures thereof. Other preferred polymers are polyethylene terephthalate and polybutylene terephthalates containing, as other monomer units, up to 1% by weight, preferably up to 0.75% by weight of 1,6-hexanediol and / or 5-methyl-1,5-pentanediol . The preferred preparation is continuous and based on DE-A 44 01 055, by: a) a first step, the esterification or transesterification of a dicarboxylic acid or its esters or ester-forming derivatives, with a molar excess of a dihydroxy compound . b) in a second step, the precondensation of the product of the transesterification or esterification obtained in (a), And c) in a third step, the polycondensation of the product that can be obtained from b) to the desired viscosity index. where steps a) and b) of the process is carried out in at least two temperature zones. Step a) of the process is called a transesterification or esterification reaction. This is carried out in at least two, and preferably at least three temperature zones. The temperature in this case of each zone must be greater than that of the previous zone by from one to 40 ° C, preferably from 2 to 30 ° C and in particular from 5 to 10 ° C. The temperature range for the entire esterification reaction is generally (depending on the starting material) from 165 to 260 ° C, preferably from 170 to 250 ° C and in particular from 180 to 240 ° C, and the pressure is generally from 1 up to 10 bar, preferably from 1 to 4 bar and, in particular, from 1 to 2 bar. Step a) of the preference process operates in at least two temperature zones with very substantially identical pressure conditions in the individual zones. The technical requirements, such as the apparatus (e.g., in the form of reactor cascades) to create different temperature zones are known to those skilled in the art, and therefore need not be described herein in greater detail. Initial materials, such as diols and acids, have already been described in the above. The reaction is usually carried out with a molar excess of diol, to exert the desired influence on the equilibrium of the ester. The molar ratios of the dicarboxylic acid and / or dicarboxylic ester to diol are usually from 1: 1.1 to 1: 3.5, preferably from 1: 1.2 to 1: 2.2. It is very particularly preferable that the molar ratios of dicarboxylic acid to diol be from 1: 1.5 to 1: 2 and of the diester to the diol be 1: 1.25 to 1: 1.5. However, it is also possible to carry out the ester reaction with a small excess of the diol in the first zone and correspondingly add other quantities of the diol in the other temperature zones. In the preferred embodiment of the novel process with three temperature zones, the total amount of the diol is divided into three zones in the following percentages: from 60 to 85 (1), from 10 to 25 (2) and from 5 to 15 (3 ), and preferably from 70 to 80 (1), from 10 to 20 (2), and from 5 to 10 (3). The times of stay for all the step a) are from 140 to 300 min, preferably from 150 to 260 min and, in particular, from 160 to 220 min, and the time of stay for the first zone is from 100 to 190 min , preferably d, is from 110 to 150 min, and for the second zone from 65 to 140 min, preferably from 65 to 110 min. For the preferred modality with three zones, the time of stay in the third zone is from 15 to 45 minutes, preferably from 15 to 30 min, with residence times in the second zone correspondingly reduced and those in the first zone being retained. as already described. In the preferred mode of the novel process, preferably stay times decrease from the first to the third zone, preferably in a ratio of 6: 3: 1. In a particularly preferred embodiment, a catalyst and then an alkali metal compound or alkaline earth metal compound are first added to the dihydroxy compound, before step a) of the process. Preferred catalysts are titanium compounds and tin compounds, as described inter alia in US 39 36 421 and US 43 29 444. Preferred compounds which may be mentioned are tetrabutyl orthotitanate and triisopropyl titanate, and also tin dioctoate, which are normally used in step a) in amounts of from 20 to 150 ppm, preferably from 20 to 120 ppm and, in particular, from 30 to 70 ppm (based on the metal). To further reduce the content of the carboxyl end group of the polyester it may be advantageous, before reacting the initial monomers, to add from 0.1 to 10 mmol, preferably from 0.2 to 0.65 mmol, of an alkali metal compound or alkaline earth metal compound ( calculated as alkali metal or alkaline earth metal) per kg of polyester. Compounds of this type are proposed in DE-A 43 33 930. Preferred compounds which may be mentioned are sodium carbonate, sodium acetate and sodium alcoholates, in particular sodium methanolate. The products of the transesterification or esterification are then transferred continuously to the precondensation step b). This has at least two temperature zones, preferably at least three and, in particular, at least four. The temperature of each zone in this case is higher than that of the preceding zone in from 1 to 40 ° C, preferably from 2 to 30 ° C and, in particular, from 5 to 20 ° C. The temperature range for the entire precondensation is generally (depending on the starting materials) from 220 to 300 ° C, preferably from 225 to 290 ° C and, in particular, from 240 to 290 ° C. The preferred precondensation is carried out with a pressure in the first zone from 0.5 to 1 bar, preferably from 0.6 to 0.8 bar, and in the second or last zone from 20 to 200 mbar, preferably from 25 to 150 mbar and, in particular, from 50 to 150 mbar. An example of a reactor that can be used in industrial form for this purpose is a vertical tubular bundle reactor, and other reactors for the purpose are known to those skilled in the art. The residence times for all step b) of the process are from 10 to 80 min, preferably from 15 to 50 min and, in particular, from 20 to 40 min. In a particularly preferred embodiment of the novel process, use is made of four temperature zones. The relationships of the zone-to-zone temperature rise are as described above, and the pressure is reduced from the first to the fourth zone within the described limits. In this embodiment of the tubular bundle heat exchanger, the fourth zone is composed of the equipment for separating the liquid and vapor phase (also called a vapor separator). The volume ratio of the steam separator to the volume in the tubes is preferably from 5 to 15: 1, in particular from 8 to 13: 1. The volume relationships of the first three zones in this particularly preferred embodiment are preferably designed in such a way that the volume constituted by the first zone is from 30 to 60%, preferably 50%, and that the content of the second zone is from 20 to 40%, preferably 30%, and that the content of the third zone is from 10 to 30%, preferably 20%. The temperature ranges, pressure ranges and residence times for the particularly preferred embodiment of the novel process are mentioned below: First zone: from 230 to 270 ° C, preferably from 240 to 250 ° C, and pressure from 0.6 to 0.9 bar, preferably from 0.7 to 0.9 bar. The time of stay from 10 to 30 min, preferably up to 25 min. Second zone; from 240 to 280 ° C, preferably from 250 to 270 ° C, and pressure from 0.2 to 0.6 bar, preferably from 0.3 to 0.5 bar. The time of .stance from 5 to 20 minutes, preferably from 5 to 7 minutes. Third zone: from 245 to 290 ° C, preferably from 250 to 280 ° C, and pressure from 0.1 to 0.3 bar, preferably from 0.1 to 0.25 bar. Time of stay from 5 to 10 minutes, preferably from 4 to 8 minutes. Fourth zone: from 250 to 300 ° C, preferably from 252 to 285 ° C, and pressure from 0.015 to 0.2 bar, preferably from 0.05 to 0.15 bar. The time of stay from 10 to 30 minutes, preferably from 14 to 24 minutes. The aforementioned catalysts for step a) of the process and other additives can be dosed in step b) of the process in the amounts mentioned. After step b) of the novel process, the polyester prepolymer has a viscosity index < 30 ml / g preferably from 20 to 30 ml / g, measured in a 0.5% solution by weight in phenol / o-dichlorobenzene (1: 1) in accordance with DIN 53728 Part 3 (1985) at 25 ° C. The polyester prepolymer is then transferred to step c) of the novel process. This is preferably carried out in a single step from 240 to 290 ° C, preferably from 240 to 270 ° C and, in particular from 240 to 265 ° C. The pressure is from 0.3 to 10 mbar, preferably from 0.3 to 5 mbar and, in particular, from 0.3 to 2 mbar. The length of stay is usually from 30 to 180 min, preferably from 35 to 150 min. During the polycondensation, the surface of the product can preferably be renewed. The surface renewal is the continuous arrival of the fresh polymer on the surface of the melt, facilitating the escape of the diol. This is preferably from 1 to 20 m / kg of product and minute [sic] and in particular from 1.5 to 6 m / kg of the product and minute [sic]. In addition, the addition of catalysts and other additives, as already described, may be advantageous to continue in this step of the process. An important feature of the novel process is that the polycondensation of the prepolymer is carried out in the presence of a gas containing oxygen. To achieve a high content of the terminal carboxyl group, these gases must contain at least 17% by volume of oxygen, preferably at least 18% by volume of oxygen, preferably using oxygen and air. To improve the dispersion, the prepolymer can be ground, for example, ground and then stirred for a period of from 30 minutes to 15 hours, preferably from 50 minutes to six hours with, for example, air at room temperature. The polycondensation is then carried out using the aforementioned process conditions, with the pressure preferably reduced in different stages, as already described for step c). After continuous polycondensation, the polyester has a viscosity index of from 60 to 180 ml / g, preferably from 90 to 160 ml / g, determined at 25 ° C in a 0.5% solution by weight in a phenol mixture / o-dichlorobenzene (weight ratio 1: 1) according to DIN 53728, Part 3 (1985). The terminal carboxyl group content after the polycondensation is at least 30%, preferably at least 40% and in particular at least 50%, based on the total of the carboxyl and OH end groups of the polymer. The content of the terminal carboxyl group is usually determined by a titration method (for example, by potentiometry). The polyalkylene arylates that can be obtained by the novel process are suitable for producing molded parts of any type. These are particularly suitable for thermoplastic molding compositions containing: A) from 10 to 100% by weight, preferably from 10 to 95% by weight of a polyalkylene arylate as claimed in claim 6, B) from 0 to 90% by weight, preferably from 5 to 80% by weight, weight of a polycarbonate or a polyamide or mixtures thereof, C) from 0 to 50% by weight, preferably from 0 to 30% by weight of other additives, where the total weight percentages of components A) to C) is 100%.

The structure of the polyalkylene arylates A) has already been described in the above. Suitable polycarbonates B) can be obtained by polymerizing aromatic dihydroxy compounds, in particular 2,2-bis (4-hydroxyphenyl) propane (bisphenol A) or its derivatives, for example with phosgene. The corresponding products are known per se and are described in the literature, and many of these are also commercially available. The amount of polycarbonate is up to 90% by weight, preferably up to 50% by weight, based on 100% by weight of components A) to C). The polyamides of the novel molding compositions generally have a viscosity index of from 90 to 350 ml / g, preferably from 110 to 240 ml / g, determined at 25 ° C in a 0.5% solution by weight in sulfuric acid 96% by weight weight concentration in accordance with ISO 307. Preference is given to semicrystalline or amorphous resins with a molecular weight (weighted average) of at least 5000, as described, for example, in US Patent 2 071 250, 2 071 251, 2 130 523, 2 130 948, 2 241 32.2, 2 312 966, 2 512 606 and 3 393 210. Examples of these are the polyamides obtained from lactams having from 7 to 13 members in the ring, for example, polycaprolactam, polycaprylactam and polylaurolactam, and also polyamides as obtained by the reaction of dicarboxylic acids with diamines. The dicarboxylic acids which can be used are alkanedicarboxylic acids having from 6 to 12 carbon atoms, in particular from 6 to 10 carbon atoms and aromatic dicarboxylic acids. Some examples that may be mentioned are adipic acid, azelaic acid, sebacic acid, dodecandioic acid, terephthalic acid and isophthalic acid. Particularly convenient diamines are alkanediamines having from 6 to 12 carbon atoms, in particular from 6 to 8 carbon atoms, and also m-xylylenediamine, di (4-aminophenyl) methane, di (4-aminocyclohexyl) methane, 2, 2-di (4-aminophenyl) propane or 2,2-di (4-aminociclohexyl) propane. Preferred polyamides are polyhexamethylenedipamide, polyhexamethylene sebacamide and polycaprolactam and also nylon 6/66 [sic], in particular with a proportion of from 5 to 95% by weight of caprolactam units. Mention may also be made of the polyamides which can be obtained, for example, by the condensation of 1,4-diaminobutane with adipic acid at elevated temperature (nylon 4, 6). Processes for preparing polyamides of this structure are described, for example, in EP-A 38 094, EP-A 38 582 and EP-A 39 524. Other suitable polyamides are those obtainable by the copolymerization of two or more of the aforementioned mpnomers or mixtures of more than one polyamide in any desired ratio. Other polyamides which have also proved to be advantageous are the partially aromatic copolyamides such as nylon 6/6, T and nylon 6/6, T with triamine content of less than 0.5% by weight, preferably less than 0.3% by weight (see EP- A 299 444). Preferred partially aromatic copolyamides with low triamine content can be prepared by the processes which are described in EP-A 129 195 and 129 196. The novel molding compositions can contain, as component C) up to 50% by weight, in particular not more than 40% by weight of other additives. The novel molding compositions can contain, as component C), from 1 to 50% by weight, preferably from 5 to 40% by weight and in particular from 10 to 30% by weight of a filler. Preferred fibrous filler materials that can be mentioned are carbon fibers, aramid fibers and potassium titanate fibers, and glass fibers in the E glass form are particularly preferred. These can be used as glass in filaments or as glass in pieces in the forms available in the trade. The fibrous filler materials may have been pre-treated on their surface with a silane compound to improve compatibility with the thermoplastics. Acicular mineral fillers are also convenient. For the purposes of the invention, the acicular mineral charge materials are the mineral charge materials with strongly developed acicular character. An example that can be mentioned is acicular wollastonite. The ore preferably has an L / D ratio (length / diameter) from 8: 1 to 35: 1, preferably from 8: 1 to 11: 1. The mineral filler material may, if desired, have been pre-treated with the aforementioned silane compounds, but pretreatment is not essential. Other filler materials that can be mentioned are kaolin, calcined kaolin, wollastonite, talc and gypsum. Other additives and processing aids that may be mentioned are amounts from 0 to 2% by weight of ethylene polymers containing fluoride. These are ethylene polymers with a fluoride content of 55 to 76% by weight, preferably 70 to 76% by weight. Examples of these are polytetrafluoroethylene (PTFE), tetrafluoroethylene copolymers or tetrafluoroethylene copolymers with relatively small proportions (generally up to 50% by weight) of copolymerizable, ethylenically unsaturated monomers. These are described, for example, in Schildknecht in Vinyl and Related Polymers, Wiley-Verlag, 1952, pages 484 to 494, and by Wall in "" Fluorpolymers "(Wiley Interscience, 1972) .These fluorine-containing ethylene polymers are present. in homogenously distributed form in the molding compositions and preferably has a particle size dso (numerical median) in the range from 0.05 to 10 μm, in particular from 0.1 to 5 μm.These small particle sizes are particularly preferably obtained by the use of aqueous dispersions of fluorine-containing ethylene polymers and incorporating these, for example, in a polyester melt The impact modifiers may be mentioned as additives and are also referred to as elastomeric polymers or elastomers, and may be present in amounts up to 20. % by weight, preferably up to 15% by weight Traditional rubbers are convenient, for example, copalimers of ethylene with reactive groups, acrylate rubber and conjugated diene polymers, for example, polybutadiene rubber and polyisoprene rubber. The diene polymers may have been hydrogenated to some degree or completely, in a manner known per se. Other examples of possible shock modifiers are hydrogenated styrene-butadiene rubber, ethylene-propylene-diene rubber, polybutylene rubbers and polyoctenamer rubbers, ionomers, block copolymers made from vinyl aromatic monomers with dienes, such as butadiene or isoprene. (known per se from EP-A 62 282) with the structure MV-, MVMV- or MW-, where these block polymers can also contain segments with random distribution, and also block-block copolymers. Polymers have proved to be particularly convenient are those of conjugated dienes, for example, polybutadiene rubber or polyisoprene rubber. Synthetic rubbers of this type are familiar to those skilled in the art and are reviewed in Ullmanns Encyklopadie der Technische Chemie, 4th edition, vol. 13, pages 595-634, Verlag Chemie GmbH, Weinheim 1977. Other additives that can be mentioned are the normal amounts of thermal stabilizers and light, lubricants, mold release agents and dyes such as dyes and pigments. Mention may also be made of esters or amides made from at least one alcohol or amine having at least three functional groups and one or more mono- or dicarboxylic acids having from 5 to 34 carbon atoms, giving preference to tetra-stearate of pentaerythritol and salts of Mg, Ca or Zn with carboxylic acids having up to 34 carbon atoms, in particular calcium stearate. Suitable flame retardants may be mentioned are halogen-free and halogen-free flame retardants, such as melamine cyanurate, magnesium carbonate and / or phosphorus, which may be present in amounts of up to 15% by weight. The properties of the final products can be controlled as desired to a high degree through the type and amount of the additives used. The novel molding compositions can be prepared by the processes known per se. In a preferred embodiment this is prepared by the addition of components B) and C) to the melt of component A). For this purpose it is convenient to use extruders, for example, single-screw or double-screw extruders, or other traditional plasticizing equipment such as Brabender mixers or Banbury mixers. The novel molding compositions have improved mechanical properties. Therefore, these are convenient for producing molded parts of any type. Applications in the electrical industry are preferred.

And emplos 1. Preparation of the prepolymer (Pl) 1 mole of DMT, 1.3 mole of 1,4-butanediol, 0.5 x 10 mole of tetrabutyl orthotitanate and 7.7 x 10-5 mole of sodium methanolate per hour were reacted continuously in a system from which the prepolymer was separated after the precondensation reaction. The temperature in the first reaction zone was 175 ° C, with a pressure of 1.03 bar and an average residence time of 184 min. The temperature in the second reaction zone was 195 ° C with a pressure of 1.03 bar and an average residence time of 65 min. The temperature in the third reaction zone was 203 ° C with a pressure of 1.04 bar and an average residence time of 40 min. The distillates produced in this case, which contained BDO, DMTG, THF and water, were separated into a column system, and DMT and BDO were reintroduced to the reaction. With a conversion of 94%, the product of the transesterification was fed to a vertical tube divided into three heating zones. The temperature in the fourth reaction zone was 242 ° C with a pressure of 700 mbar and an average residence time of 22 min. The temperature in the fifth reaction zone was 246 ° C with a pressure of 400 mbar and an average residence time of 12 min. The temperature in the sixth reaction zone was 248 ° C with a pressure of 150 bar and an average residence time of 6 min. The temperature in the seventh reaction zone was 247 ° C with a pressure of 50 mbar and an average residence time of 18 min. The precondensate had an IV of 26 ml / g, a terminal hydroxyl group (HEC) content of 463 meq / kg and a terminal carboxyl group (CEC) content of 12 meq / kg. The precondensate was ground and, without further addition of catalyst, transferred to a polycondensation reactor. 2. Preparation of the prepolymer (P2) 1 mole of DMT, 1.4 mole of 1,4-butanediol, 0.5 x 10 mole of tetrabutyl srtotitanate and 7.7 x 10"mole of sodium methanolate per hour were reacted continuously in a system from which a prepolymer was separated after a process of precondensation reaction. The temperature in the first reaction zone was 165 ° C, with a pressure of 1.03 bar and an average residence time of 184 minutes. The temperature in the second reaction zone was 175 ° C with a pressure of 1.03 bar and an average residence time of 65 minutes. The temperature in the third reaction zone was 205 ° C with a pressure of 1.04 bar and an average residence time of 40 minutes. The distillates produced in this case, which contained BDO, DMTG, THF and water, were separated into a column system. DMT and BDO were reintroduced to the reaction.

With a conversion of 96%, the product of the transesterification was fed to a vertical tube divided into four heating zones. The temperature in the fourth reaction zone was 242 ° C with a pressure of 700 mbar and an average residence time of 22 minutes. The temperature in the fifth reaction zone was 246 ° C with a pressure of 400 mbar and an average residence time of 12 minutes. The temperature in the sixth reaction zone was 248 ° C with a pressure of 150 mbar and an average residence time of 6 minutes. The temperature in the seventh reaction zone was 247 ° C with a pressure of 50 mbar and an average residence time of 18 minutes. The precondensate had an IV of 29 ml / g, a content of terminal hydroxyl groups (HEC) of 545 meq / kg and a terminal carboxyl group content (CEC) of 10 meq / kg.

The precondensate was ground and, without further addition of catalyst, transferred to a polycondensation reactor. 3. Polycondensation with air The pulverized prepolymer (Pl and P2, respectively) was transferred to a 1 liter polycondensation reactor with anchor stirrer and then aerated (10 1 / h) overnight at 23 ° C. The melting (23 ° C internal temperature) was followed by evacuation of the reactor in six stages (750, 500, 250, 100, 50 mbar, 1 mbar), and the contents were polycondensed with agitation (30 rpm and finely 15 rpm) to 250 ° C. After reaching the maximum viscosity (160 min), the vacuum was released and the product separated. The resulting product had the following constitution. 4. Comparative example Polycondensation under nitrogen The experiment was carried out as described in Example 1, but after the pulverized prepolymer (AC1 and AC2, respectively) had been transferred to the polycondensation reactor it was covered with nitrogen (10 1 / h) at 23 ° C during the night. The polycondensation was carried out in a similar way, but without gas introduced during the condensation and the final pressure reached was 0.4 mbar.

After 160 minutes, the vacuum was released and the product separated. The comparative products obtained had the following constitution: . Processing to obtain molded compositions: The polymers obtained from Examples (Al and A2) and also from the Comparative Examples (ACl and AC2) were mixed with polycarbonate prepared from bisphenol A with an IV of 64 ml / g (Lexan® 61 from GEP) in an extruder double helix (ZSK 30, 200 rpm, 10 kg / h of performance and 250 ° C). The formulation consisted of 50% polycarbonate. The mechanical properties were determined in accordance with the ISO standards given below.

The IV was measured at 25 ° C in a 0.5% concentration solution of the polymer in a 1: 1 mixture of phenol and o-dichlorobenzene. The IV of the PC extract was measured in CH2CI2 at 23 ° C. The content of the terminal carboxyl group (CEC) was determined by potentiometric titration of the acetic acid released when a sample of the polymer was dissolved in nitrobenzene and reacted with a defined excess of potassium acetate.

Claims (1)

1. CLAIMS A process for preparing polyalkylene arylates by esterification or transesterification of aromatic dicarboxylic acid or its esters or ester-forming derivatives with a molar excess of an aliphatic dihydroxy compound and the polycondensation of the resultant esterification or transesterification product, which consists of polycondensing the prepolymer with a viscosity index (IV) of < 30 ml / g in the presence of a gas containing oxygen. The process as claimed in claim 1, wherein the polyalkylene arylate has a viscosity index (IV) of at least 60 ml / g after the polycondensation. The process as claimed in claim 1 or 2, wherein the oxygen-containing gas contains at least 17% by volume of oxygen. The process as claimed in any of claims 1 to 3, wherein the oxygen-containing gas used is air. The process as claimed in any of claims 1 to 4, wherein a polyalkylene terephthalate is used.