Title of Invention

"METHOD FOR MAKING POLYESTER"

Abstract

Process for the manufacture of polyester comprising the following stages: a) esterification or transesterification by a diol of a dicarboxylic acid or of a dicarboxylic acid diester as hereindescribed at a temperature of 130°C to 280°C; b) prepolymerizing in a manner as herein described of the esterification or transesterification product in the liquid phase up to a mean degree of polymerization of 10 and 50, preferably between 20 and 45; c) preparaing of a dispersion of prepolymer in a liquid which is not a solvent of the diol and which does not swell the prepolymer, the prepolymer being present in the dispersion in the form of solid crystalline particles with a diameter of less than 2 mm and with a thickness of the crystalline lamellae of less than 17 nm; d) polymerization in a known manner in the dispersed solid phase; e) recovery of the solid particles.

Full Text

The present invention relates—to the method for making polyester type and more particularly to the solid-phase condensation of a polyester. The main method for producing polymers of polyester type consists of a high-temperature condensation either of the esterification product of a dicarboxylic acid by a diol or of the trans-esterification product of a diester by a diol. This condensation is carried out in the molten state. To produce poly(ethylene terephthaiate) (PET), the product of the transesterification of methyl terephthaiate (DMT) by ethylene glycol (EG) or the product,of the esterification of purified terephthalic acid (PTA) by ethylene glycol is condensed. The condensation is carried out until a compound of the desired molecular, weight is obtained. This condensation cannot result in polymers having a very high viscosity number, in particular of greater than 85 ml/g. The type of technology currently employed does not allow the reaction to be continued above such a viscosity. If it is desired to obtain polymers of high molecular weight, it is therefore necessary to carry out a postcondensation in the solid state at temperatures of the order of 200°C. This postcondensation consists in heating a charge of polymer granules. This solid-phase and low-temperature process makes it possible in particular to obtain polymers with a low level of decomposition. Du Pont de Nemours, in particular in patents US 5 548 868 and US 5 510 454, discloses another method for preparing polyesters. This method consists in producing prepolymer pellets, which products are crystalline, so as to render them sufficiently reactive, and have very low degrees of polymerization of between 2 and 40. The pellets are subsequently condensed in the solid state according to the process described above for the postcondensation. It is possible, by this method, to obtain polymers of all molecular weights with viscosity numbers of less than or greater than approximately 85 ml/g, depending upon the operating conditions of the postcondensation. The solid-phase condensation and postcondensation processes described above have rather slow kinetics and constitute a limiting stage in the manufacture of polyesters. Despite the progress achieved, continual efforts are being made to improve the performance of the solid-phase condensation or postcondensation stage. An object of the present invention is to overcome the problems posed by the solid-phase condensation by providing a process which makes it possible to increase the kinetics of the solid-phase condensations. It provides an alternative to the known processes by employing a condensation in the dispersed solid phase in a liquid. This makes it possible to avoid the difficulties encountered with the conventional process, to increase the kinetics of condensation and thus to arrive more rapidly at the desired degrees of polymerization. The implementation of the condensation in the dispersed solid phase in a liquid medium has to be carried out on a solid prepolymer having specific properties necessary for the process to be carried out satisfactorily and for the acceleration of the kinetics. Another subject-matter of the invention is thus a process for producing the prepolymer to be condensed in the dispersed solid phase and its characteristics and in particular the crystalline characteristics which allow it to be rendered sufficiently reactive. The invention introduces a process for the manufacture of polyester which comprises at least the stages described below. It can comprise other upstream, downstream or intermediate stages. The stages of the process can be carried out continuously or batchwise, in devices separated from one another or within the same devices. The essential stages are as follows: a) esterification or transesterification by a diol of a dicarboxylic acid or of a dicarboxylic acid diester, b) prepolymerization of the esterification or transesterification product in the liquid phase up to a mean degree of polymerization of between 10 and 50, preferably between 20 and 45, c) preparation of a dispersion of prepolymer in a liquid which is not a solvent of the diol and which does not swell the prepolymer, the prepolymer being present in the dispersion in the form of solid crystalline particles with a diameter of less than 2 mm and with a thickness of the crystalline lamellae of less than 17 nm, d) polymerization in the dispersed solid phase, e) recovery of the solid particles. The process can be applied to the polymerization of any dicarboxylic acid with any diol. It can be applied in particular to the following diacids: terephthalic acid, isophthalic acid, naphthalenedioic acid, 5-sulfoisophthalic acid and their mixtures. It can be applied in particular to the following diols: ethylene glycol, butanediol, neopentyl glycol, diethylene glycol, bisphenol, 1,3-propanediol, 1,2-propanediol, cyclohexyldimethanol and their mixtures. The process can be applied more particularly to the synthesis of poly(ethylene terephthalate) from the monomers of terephthalic acid or of methyl terephthalate and of ethylene glycol. Stage a), of esterification or of transesterification, is a stage commonly carried out in industrial processes for the manufacture of polyesters. Two routes are mainly employed, for example, for the manufacture of poly(ethylene terephthalate). The first preparation route is the "methyl terephthalate" (DMT) route. It is a transesterification reaction. The molten DMT is dissolved in the ethylene glycol (EG), present in excess, the EG/DMT molar ratio being approximately 1.9 to 2.2, and the reaction is carried out at atmospheric pressure at temperatures from approximately 130°C to 250°C. It requires the presence of a catalyst, such as, for example, manganese acetate. The methanol given off by the reaction is removed by distillation. The excess ethylene glycol present is removed by evaporation after the transesterification reaction. The catalyst, which is also a catalyst for the decomposition of the polyester, is blocked after the reaction using phosphorus compounds. The product resulting from the transesterification is a mixture of bis(hydroxyethyl) terephthalate (BHET) and of oligomers. The second route is the "direct esterification" route. It is a reaction for the esterification of terephthalic acid by ethylene glycol. It is carried out at temperatures of 130°C to 280°C. The terephthalic acid, which is molten at these temperatures, is not soluble in the ethylene glycol but is soluble in the ester produced from the reaction. The solubilization of the reactant in the medium is thus progressive. The ethylene glycol is present with an EG/terephthalic acid molar ratio of approximately 1 to 3. This reaction results in a mixture of oligomers having end functional groups in the form of terephthalic acid or of hydroxyethyl terephthalate. The use of these processes has formed the subject of numerous studies described in the literature. The conditions indicated above do not constitute a limitation to the scope of the present invention. The subsequent stages of prepolymerization and of solid phase polymerization are stages of polymerization by condensation. They are generally catalyzed using metal compounds, for example by antimony, titanium or germanium compounds. They can be catalyzed by any polycondensation catalyst disclosed in the prior art. Stage b), of liquid phase prepolymerization, can preferably be carried out according to two embodiments. The first embodiment consists in carrying out the prepolymerization in the molten phase. The second embodiment consists in carrying out the prepolymerization in the dispersed molten phase in a liquid medium. The implementation of these two embodiments will be described subsequently. The prepolymer obtained has a mean degree of polymerization of between 10 and 50, preferably between 20 and 45. The term "mean degree of polymerization" is understood to mean the absolute mean degree of polymerization defined by the following formula: (Formula Removed) of the repeat unit of the polymer, Mx is the molar mass of the chain with the size referenced i and nx is the number of chains with the size referenced i. The molar masses are the absolute molar masses .- The mean degree of polymerization is related to the absolute number-average molar mass Mn according to the above formula. The latter is evaluated by Gel Permeation Chromatography (GPC) coupled to viscometry. The viscosity of the polymer in solution is related to the length of the chains and thus to the number-average molar mass and to the mean degree of polymerization. This is an indicator of the progress of the polymerization. In the present document, the term "viscosity number" (VN) is understood to mean the viscosity in ml/g measured at 25°C using a viscometer of Ubbelohde type for a 0.005 g/ml solution of polymer dissolved at 115°C in a mixture composed of 50% by weight of phenol and 50% by weight of 1 , 2-dichlorobenzene . A correlation between the viscosity number and the mean degree of polymerization, evaluated by GPC, was established for the PET: DPn = 1.19*VN-7 where VN is in ml/g. This correlation is valid for viscosity numbers of between 10 and 70 ml/g. Stage c) consists in producing a dispersion in a liquid of prepolymer resulting from stage b). The dispersed prepolymer is in the form of solid particles. The dispersing liquid used must not be a solvent of the diol and must not be a medium which swells the prepolymer. For the implementation of: the subsequent stage of polymerization in a dispersed solid phase, the solid particles must have a diameter of less than approximately 2 mm, preferably 1 mm, and must be crystalline with a thickness of the crystalline lamellae of less than approximately 17 nm, preferably less than approximately 12 nm. The dispersion of solid particles can be formed according to several methods. The methods for the formation of the dispersion can depend in particular on the embodiment of the prepolymerization stage. Two types of methods for the formation of [lacuna] dispersion are singled out: a first embodiment of the dispersion consists in solidifying the prepolymer in the form of particles and in isolating it (first phase), and then in bringing together the particles and the dispersing medium (second phase). A second embodiment of the dispersion consists in carrying out the two phases simultaneously, the solidification of the prepolymer taking place within the dispersing medium. These embodiments will be described in detail subsequently. Stage d) , of polymerization in the dispersed solid phase in a liquid medium, makes it possible to obtain high kinetics of polymerization in the case where the solid prepolymer particles have the characteristics described above and are obtained by the processes described, for example, in the present document. The stage of polymerization in the dispersed solid phase in a liquid medium must be carried out in a medium which is not a solvent of the diol reacted and which does not swell the prepolymer. More particularly, for the manufacture of poly(ethylene terephthalate), the medium must not be a solvent of ethylene glycol. The purpose of this characteristic is to make possible the removal of the diol and to accelerate the polymerization reaction. Mention may be made, as liquids suitable for the implementation of the invention, of hydro-carbonaceous compounds. These compounds can result, for example, from an aliphatic hydrocarbon fraction in which the hydrocarbons have a number of carbon atoms of less than or equal to 20. The hydrocarbon fraction can be a product which is liquid at atmospheric pressure at the temperature of the dispersed phase polymerization. The condensation in the dispersed solid phase can also advantageously be carried out in a hydrocarbon fraction which is a gas at atmospheric pressure at a temperature of greater than 150°C and which is kept in the liquid state under pressure during the polymerization in the dispersed solid phase. Such a medium is removed by reduction in pressure at the end of the process, in order to recover the polymer. The removal of the diol within the medium is facilitated by entrainment by a stream of inert gas. The gas can advantageously be introduced by sparging into the dispersing medium. It can be chosen, for example, from nitrogen, rare gases, gases which have been rendered inert, such as, for example, air enriched in nitrogen, carbon dioxide and their mixtures. The presence of the inert gas furthermore makes it possible to prevent any presence of oxygen within the medium and thus to prevent any decomposition of the polyester. The entrained dispersing medium can be recycled in the reaction medium after collecting and separating from the diol. In order to stabilize the dispersion of the solid prepolymer particles to be condensed, it is possible, without this having to constitute a limitation to the process described, to add an agent to the liquid medium. This stabilizing agent is advantageously a compound having surface-active properties which comprises a polar part and a nonpolar part and which does not comprise any functional group which is reactive in the medium. It can, for example, be chosen from protected poly(ethoxylated) alkylphenols, for example protected poly(ethoxylated) nonylphenol, and protected poly(ethoxylated) alkanes. Protection is achieved by alkoxylation, for example by penthoxylation for poly(ethoxylated) nonylphenols or by methoxylation for poly(ethoxylated) alkanes. Mention may be made, as example of protected ,poly(ethoxylated) alkane, of the C14 alkane ethoxylated 11 to 12 times. The polymerization in the dispersed solid phase is carried out at temperatures at which the dispersed particles are in the solid state. The temperature can vary during the progress of the reaction, generally by increasing, but must always remain below the temperature which results in the melting of the particles present in the medium which are the most readily melted. The presence of particles in the molten state facilitates the phenomena of aggregation of particles and reduces the polymerization rate. For example, the polymerization in the dispersed solid phase can be carried out at a temperature lower by 10°C than the melting temperature of the dispersed polymer. The dispersion is characterized in that the solid particles have a diameter of less than 2 mm. The term "diameter" is understood to mean the mean diameter of the dispersed particles. The diameter of the solid particles is preferably less than 1 mm. The dispersed particles must exhibit crystalline characteristics specific for the implementation of a condensation in the dispersed solid phase. The thickness of the crystalline lamellae of the particles must be less than approximately 17 nm and preferably less than approximately 12 nm. The term "thickness of the .crystalline lamellae" is understood to mean the length measured by wide angle diffraction (WAXS) according to the following reference: N.S. Murphy and H. Minor, "General procedure for evaluating amorphous scattering scans cristallinity from X-ray diffraction scans of semicristalline polymers", Poly., vol. 31, 996-1002 (1990). This method consists in locating the diffraction peak corresponding to the crystalline reflection with respect to the plane of Miller indices (010) at a 2(3 angle of 17.8°. The mean ACS010 dimension of the crystal is given by the Scherrer equation: ACS010 = k*l/ (a*cosß), where k = 0.9, 1 is the wavelength of copper and a is the width at mid-height in radians of the diffraction peak. The formation of the solid particles and their dispersion, simultaneous or subsequent, in the dispersing medium which is not a solvent of the diol and which does not swell the prepolymer can depend on the embodiment of the prepolymerization stage b). Two embodiments of the prepolymerization are suitable for the implementation of the invention. The first method of prepolymerization is a prepolymerization in the molten phase dispersed as droplets in a liquid medium. It is carried out by bringing together a heated liquid medium and a molten product of the type of that obtained by stage a), to which a catalyst is optionally added. This medium must not be a solvent of the compounds involved. The medium can be exactly the same as that prepared for the subsequent polymerization in the dispersed solid phase. It can be different from that which will subsequently be used. It can thus be composed of the same types of components, for example hydrocarbons, be subjected identically to a gas stream and comprise one or more stabilizers. The addition of a stabilizer can, in addition, make it possible to exert better control over the dispersion of the molten prepolymer and to prevent coalescence of the droplets. The use of the C14 alkane ethoxylated 11 to 12 times and protected by methoxylation gives particularly outstanding results. The characteristics of the media have been described in detail above. The reaction temperature must be controlled in order to keep the compound to be prepolymerized in the molten state, for example above 220°C. It can be increased during the reaction, for example to approximately 260°C. The prepolymerization is carried out until a mean degree of polymerization of between 10 and 50, preferably between 20 and 45, is obtained. At this stage of the process, the prepolymerization product is found dispersed in the molten state in a dispersing medium with a temperature greater than the melting temperature of the prepolymer. The second method of prepolymerization is a prepolymerization in the molten phase. It is carried out by heating product of the type of that obtained by stage a), to which a catalyst is optionally added, the product being in the liquid state and constituting the mass of the medium. The prepolymerization in the molten phase can be carried out as follows. A mixture of compound to be prepolymerized and of catalyst is heated to a temperature greater than the melting temperature of said compound, above 200°C, preferably above approximately 260°C. The reaction can advantageously be carried out under reduced pressure in order to promote the evolution of ethylene glycol and optionally of water when the precursor employed in stage a) is a dicarboxylic acid. It can optionally be carried out while flushing or sparging with inert gas. This facilitates the removal of the ethylene glycol present in the medium. The prepolymerization is carried out until a mean degree of polymerization of between 10 and 50, preferably between 20 and 45, is obtained. At this stage of the process, the prepolymerization product is found in the molten state isolated from any dispersing medium. The prepolymerization product according to the embodiment in the molten phase can be converted to the form of crystalline and dispersed solid particles according to several methods. The crystallization is carried out at a temperature within the range of the crystallization temperatures of the prepolymer. This range is between the following temperatures: glass transition temperature plus 25% of the difference between the melting and glass transition temperatures and melting temperature minus 25% of the same difference. A first method consists in rapidly solidifying the molten prepolymer and in forming it as solid particles with a diameter of less than 2 mm, preferably 1 mm, and in then bringing together the particles obtained and the dispersing medium which is not a solvent of the diol. The forming can be carried out, for example, by milling or by sectioning rods with a diameter of less than 2 mm, preferably 1 mm. A second method consists in spraying the prepolymerization product into a gaseous fluid with a temperature within the range of the crystallization temperatures of the prepolymer. The spraying must be carried out in the form of droplets with a diameter of less than 2 mm, preferably 1 mm. The droplets, solidified on contact with the gas, are subsequently combined with the dispersing medium which is not a solvent of the diol and which does not swell the prepolymer. A third embodiment consists in spraying the prepolymerization product into the dispersing medium which is not a solvent of the diol and which does not the swell the prepolymer, said medium being at a temperature within the range of the crystallization temperatures of the prepolymer. The solidification and the formation of the dispersion are simultaneous here. A fourth embodiment comprises a first phase which consists in spraying the prepolymerization product into the dispersing medium which is not a solvent of the diol and which does not swell the prepolymer, said medium being at a temperature greater than the melting temperature of the prepolymer. After this first phase, the prepolymerization product is found dispersed in the molten state in a dispersing medium with a temperature greater than the melting temperature of the prepolymer. When the prepolymerization product is found dispersed in the molten state in a dispersing medium with a temperature greater than the melting temperature of the prepolymer, either on conclusion of the first phase of the fourth method for dispersing after a prepolymerization in the molten phase or on conclusion of a prepolymerization in the dispersed molten phase in a liquid medium, the dispersion can mainly be prepared according to two embodiments. In a first embodiment, the dispersing medium is rapidly cooled to a temperature within the range of the crystallization temperatures of the prepolymer. This.cooling can, for example, be carried out by dilution with cold liquid constituting the dispersing medium. The product resulting from this cooling is the suspension of solid particles in a liquid which is not a solvent of the diol and which does not swell the prepolymer. A second embodiment can be employed if the liquid medium for dispersing the molten phase is a product which is a gas at a temperature of greater than 150°C and is kept under pressure in the liquid state. This method consists in reducing the pressure of the medium at a temperature within the range of the crystallization temperatures of the prepolymer and in thus solidifying the initially molten prepolymer in suspension. The particles are subsequently combined with the dispersing medium which is not a solvent of the diol and which does not swell the prepolymer. The sequence, within the same medium, of the stages of prepolymerization in the dispersed molten phase, of the preparation of the dispersion of the solid particles and of polymerization in the dispersed solid phase is a particularly simple and effective embodiment. Stage e) is a stage during which the product from the polymerization in the dispersed solid phase in a liquid medium is isolated from the dispersing medium. The isolation can be carried out by any means which makes possible the separation of a suspended solid phase from a liquid phase. The isolation can consist, for example, of a filtration, a separation by settling or a destabilization of the dispersion. If the dispersing medium is a liquid medium composed of a compound which is a gas at atmospheric pressure and which is liquefied under pressure, the isolation can be carried out by reducing the pressure of the medium. The solid particles can be washed by any appropriate compound and then dried. Mention may be made, as washing compound, of, for example, heptane. The solid particles can be used directly for applications, for example for extrusion, or can be compacted in the form of pellets or granules. Other details or advantages of the invention will become more clearly apparent in the light of the examples given below solely by way of indication. Example 1 A poly(ethylene terephthalate) prepolymer with a viscosity number (initial VN) of 42 ml/g, that is to say with a mean degree of polymerization of 43, is prepared according to a conventional direct esterification process, in the molten phase, from purified terephthalic acid and ethylene glycol, in the presence of 250 ppm of catalyst. The catalyst used is antimony oxide. The prepolymer is solidified in bulk and then milled with dry ice. The product from the milling is sieved. The various particle sizes are separated into the samples, the particles of which have diameters of between 125 and 250 µm, 250 and 500 ↨0m and 500 and 1000 µm respectively. The sieved powders are dried under vacuum at 130°C for 3 hours. The thickness of the crystalline lamellae is measured: 11.5 nm. The powders are dispersed in 100 ml of a C14-C17 hydrocarbon fraction (sold by Halterman) in a 0.5 1 round-bottomed reactor equipped with a stirring system, with a condenser of Dean and Stark type coupled to a reflux condenser, with a thermocouple and with an argon inlet surmounted by a sampling chamber, the reactor being maintained under argon. The level of solid introduced (mass of solid prepolymer introduced in the form of powder with respect to the mass of dispersing medium) is 6.2%. The round-bottomed flask is heated. The temperatures within the dispersing medium are measured using the thermocouple. The polymerization in the dispersed solid phase is carried out at various heating temperatures for a particle size of between 125 and 250 µm. The progress of the polymerization is measured by the change in the viscosity number (VN). The viscosity numbers measured after polymerizing in the dispersed solid phase for approximately 8 hours (VN 8 hours) are presented in Table 1 for heating temperatures of 200°C to 240°C. The polymer is recovered by filtration. The polymer powder obtained is rinsed several times with heptane and dried under vacuum at 70°C for a few hours. Table 1 (Table Removed) Polymerizations in the dispersed solid phase are carried out according to the same embodiment, at a temperature of 220°C, for various sizes of particles isolated by sieving. The viscosity numbers measured after polymerizing in the dispersed solid phase for approximately 8 hours (VN 8 hours) are presented in Table 2 for particle sizes of between 125 and 250 µm, 250 and 500 µm, and 500 and 1000 µm respectively. Table 2 (Table Removed) Comparative examples The effectiveness of a polymerization in the dispersed solid phase in a liquid medium is compared with the effectiveness of a conventional condensation in the solid phase in a gaseous medium (conventional postcondensation). A condensation in the solid phase in a gaseous medium is carried out on a prepolymer powder with a viscosity number of 42 ml/g, a crystalline lamella thickness of 11.5 nm and a particle size of between 125 and 250 µm. This powder is obtained according to the embodiment described in Example 1. The powder is placed in a 100 ml round-bottomed flask attached to a device which allows it to rotate about its axis. The rotating round-bottomed flask is immersed in a heated bath of silicone oil, so that the temperature of the powder is 220°C. The system is flushed with a stream of nitrogen. The progress of the condensation is measured by the change in the viscosity number (VN). The viscosity numbers measured after condensing, for approximately 8 hours (VN 8 hours), either a dispersed solid phase in a gaseous medium or in dispersed solid phase in a liquid medium are presented in Table 3. The condensation in the dispersed solid phase in a liquid medium is carried out under the same conditions at 220°C for a powder with granules with a size of between 125 and 250 µm. This implementation is described in Example 1. The results obtained following identical implementations with a condensation temperature of 200°C are presented in Table 4. Table 3 (Table Removed) Table 4 (Table Removed) Example 2 Condensations were carried out on prepolymers with various degrees of polymerization (initial DPn) . The thickness of the crystalline lamellae (t) is measured and presented in Table 5. These prepolymers are prepared in the same way as for the preceding examples. The condensations in the dispersed solid phase in a gaseous medium (CS) and in the dispersed solid phase in a liquid medium (CSd) are carried out according to the same process. The implementational conditions are as follows: - particle size: 125 µm to 250 µm - condensation temperature: 220°C Table 5 (Table Removed) Examp1e 3 This example illustrates an embodiment according to which the prepolymerization is carried out in the dispersed molten phase in a liquid medium. A 0.5 liter round-bottomed reactor, equipped with a stirring system, with a condenser of Dean and Stark type coupled to a reflux condenser and to a dropping funnel, with a thermocouple and with an argon inlet surmounted by a sampling chamber maintained under this gas, is set up. 100 g of the product resulting from the "esterification of terephthalic acid (PTA) by ethylene glycol are charged to the reactor. It is melted and 270 ppm of antimony acetate are added with respect to the initial mass of PTA, this antimony acetate being diluted in ethylene glycol and being introduced onto the molten transesterification product using a syringe. 100 ml of a C14 to C17 aliphatic hydrocarbon fraction, heated beforehand at 250°C, are introduced using the dropping funnel. A constant flow rate of 15 ml/s of argon is maintained in the reactor throughout the synthesis. The synthesis is carried out at atmospheric pressure. The reactor is heated using a silicone oil bath. The temperature is maintained at 250°C for 2 hours. The product is found in the dispersed molten state in the hydrocarbon fraction. Quenching is carried out by the addition of the hydrocarbon fraction at 20°C, resulting in a 4 fold "dilution. All the liquid-liquid suspension is then dispersed as solid prepolymer particles in the liquid medium. The prepolymer obtained is washed with heptane [lacuna] at 70°C under vacuum for a few hours. It is subsequently sieved to diameters of less than 250 µm. 20 g of prepolymer powder thus prepared and 200 ml of hydrocarbon fraction are introduced into the reactor. The temperature of the reactor is subsequently brought to 220°C. This temperature is maintained for 8 hours. During the condensation, ethylene glycol (reaction byproduct) and the hydrocarbon fraction are entrained by the argon flow. They are condensed in the Dean and Stark apparatus, where a phase separation makes it possible to collect the ethylene glycol, whereas the supernatant (the hydrocarbon fraction) returns to the reactor, thus making it possible to maintain a constant dilution of polymer in the diluting medium. After condensing for eight hours, the polymer powder obtained is rinsed several times with heptane and dried under vacuum at 70°C for a few hours. The viscosity numbers (VN) and thicknesses of the crystalline lamellae are evaluated on the prepolymer (after quenching) and then on the polymer after condensing for eight hours in the dispersed solid phase in a liquid medium. The results are presented in Table 6. Table 6 (Table Removed) WE CLAIM; 1. Process for the manufacture? of polyester comprising the following stages: a) esterification or transesterification by a diol of a dicarboxylic acid or of a dicarboxylic acid diester as hereindescribed at a temperature of 130°C to 280°C; b) prepolymerizing in a manner as herein described of the esterification or transesterification product in the liquid phase up to a mean degree of polymerization of 10 and 50, preferably between 20 and 45; c) preparing of a dispersion of prepolymer in a liquid which is not a solvent of the diol and which does not swell the prepolymer, the prepolymer being present in the dispersion in the form of solid crystalline particles with a diameter of less than 2 mm and with a thickness of the crystalline lamellae of less than 17 nm; d) polymerization in a known manner in the dispersed solid phase; e) recovery of the solid particles. 2. Process as claimed in claim 1, wherein the dicarboxylic acids are chosen from terephthalic acid, isophthalic acid, naphthalenedioic acid, 5-sulfoisophthalic acid and their mixtures. 3. Process as claimed in either of claims 1 and 2, wherein the diol is chosen from ethylene glycol, butanediol, neopentyl glycol, diethylene glycol, bisphenols, 1,3-propanediol, 1,2-propanediol, cyclohexyldimethanol and their mixtures. 4. Process as claimed in any one of claims 1 to 3, wherein the prepolymerization stage b) is catalyzed in manner as hereindescribed. 5. Process as claimed in any one of claims 1 to 4, wherein the stage d) of polymerization in the dispersed solid phase is catalyzed in a known manner. 6. Process as claimed in any one of claims 1 to 5, wherein the thickness of the crystalline lamellae of solid particles which are obtained by stage c) is less than 12 nm. 7. Process as claimed in any one of claims 1 to 6, wherein the diameter of the solid particles which are obtained by stage c) is less than 1 mm. 8. Process as claimed in any one of claims 1 to 7, wherein the liquid medium for dispersing the solid particles is a hydrocarbon fraction. 9. Process as claimed in claim 8, wherein the dispersing compounds of the hydrocarbon fraction are aliphatic and have a number of carbon atoms of less than 20. 10. Process as claimed in claim 1, wherein the dispersing medium comprises a stabilizing compound having surface-active properties, chosen from protected poly (ethoxylated) alkylphenols and protected poly (ethoxylated) alkanes. 11. Process as claimed in one of claims 1 to 13, wherein the polymerization in the dispersed solid phase is carried out under a stream of inert gas. 12. Process as claimed in claim 11, wherein the inert gas is chosen from nitrogen, rare gases, gases which have been rendered inert, air enriched in nitrogen, carbon dioxide and their mixtures. 13. Process as claimed in one of claims 1 to 12, wherein the polymerization in the dispersed solid phase is carried out at temperatures below the melting temperature of the particles present in the medium which are the most readily melted. 14. Process as claimed in one of claims 1 to 13, wherein the prepolymerization is carried out in the dispersed molten phase in a liquid medium. 15. Process as claimed in claim 14, wherein the medium for dispersing the molten phase comprises a stabilizing compound having surface- active properties, chosen from protected poly (ethoxylated) alkylphenols and protected poly (ethoxylated) alkanes. 16. Process as claimed in one of claims 14 and 15, wherein the liquid medium for dispersing the molten phase is a hydrocarbon fraction. 17. Process as claimed in claim 16, wherein the compounds of the hydrocarbon fraction are aliphatic and have a carbon number of less than 20. 18. Process as claimed in claim 14, wherein the stages of prepolymerization in the dispersed molten phase and of polymerization in the dispersed solid phase are carried out in the same liquid medium according to one of claims 8 to 10. 19. Process as claimed in one of claims 1 to 18, wherein the prepolymerization is carried out in the molten phase. 20. Process as claimed in claim 19, wherein stage c) comprises a phase of rapid solidification of the molten prepolymer, a phase of formation of particles with a diameter of less than 2 mm and a phase of mixing the granules or particles with the dispersing medium. 21. Process as claimed in claim 20, wherein the formation of particles is carried out by milling. 22. Process as claimed in claim 20, wherein the solidification is carried out in the form of rods with a diameter of less than 2 mm and in that the formation of particles is carried out by sectioning said rods. 23. Process as claimed in claim 19, wherein stage c) comprises a phase of formation of solid prepolymer particles by spraying the prepolymer in the molten state, in the form of droplets with a diameter of less then 2 mm, into a gaseous fluid with a temperature within the range of the crystallization temperatures of the prepolymer and a phase of mixing the solid particles obtained with the dispersing medium. 24. Process as claimed in claim 19, wherein stage c) comprises a phase of formation of solid prepolymer particles by spraying the prepolymer in the molten state, in the form of droplets with a diameter of less than 2 mm, into a liquid fluid as claimed in any one of claims 8 to 10 with a temperature within the range of crystallization temperatures of the prepolymer. 25. Process as claimed in claim 19, wherein stage c) comprises a phase of spraying prepolymer in the molten state, in the form of droplets with a diameter of less than 2 mm, into a liquid with a temperature greater than the melting temperature of the prepolymer and a phase of solidification and crystallization. 26. Process as claimed in claim 25, wherein the liquid is the dispersing medium of stage d) of polymerization in the dispersed solid phase as claimed in one of claims 8 to 10. 27. Process as claimed in claim 25, wherein the liquid is a hydrocarbon fraction which is a gas at atmospheric pressure at a temperature of greater than 150°C, kept under pressure in the liquid state. 28. Process as claimed in claim 27, wherein the dispersion is produced by solidification of the droplets by reducing the pressure of the liquid medium to atmospheric pressure and then by mixing the solid particles obtained with the dispersing medium. 29. Process as claimed in any one of claims 14 to 18 and 26, wherein stage c) comprises solidification of the suspension of the molten prepolymer by cooling to a temperature within the range of the crystallization temperatures of the prepolymer. 30. Process as claimed in claim 29, wherein the cooling is carried out by dilution with cold dispersing liquid.

Documents:

in-pct-2001-553-del-abstract.pdf

in-pct-2001-553-del-claims.pdf

in-pct-2001-553-del-complete specification (as filed).pdf

in-pct-2001-553-del-complete specification (granted).pdf

in-pct-2001-553-del-correspondence-others.pdf

in-pct-2001-553-del-correspondence-po.pdf

in-pct-2001-553-del-description (complete).pdf

in-pct-2001-553-del-form-1.pdf

in-pct-2001-553-del-form-13.pdf

in-pct-2001-553-del-form-19.pdf

in-pct-2001-553-del-form-2.pdf

in-pct-2001-553-del-form-3.pdf

in-pct-2001-553-del-form-6.pdf

in-pct-2001-553-del-gpa.pdf

in-pct-2001-553-del-pct-210.pdf

in-pct-2001-553-del-pct-409.pdf

in-pct-2001-553-del-pct-416.pdf

in-pct-2001-553-del-petition-137.pdf

in-pct-2001-553-del-petition-138.pdf