WO2001088004A2 - High molecular weight polyester polymer, method for making same and use thereof - Google Patents

Abstract

The invention concerns a polyester-type polymer, a method for making said polymer and its use for making articles. More particularly, the invention concerns a polyester with high molecular weight and viscosity in melted state enabling said polymer to be used in processes for manufacturing articles by extrusion and pultrusion, for example or more generally shaping processes which require a polymer with high viscosity in melted medium to avoid or limit deformation in the shaped article before solidification of the material. The inventive polymer has an absolute molecular weight in volume Mw higher than 130000 and a viscosity in melted state higher than 8040 Pa.s.

Description

 POLYMERS OF THE HIGH MOLECULAR WEIGHT POLYESTER TYPE. PROCESS FOR THE MANUFACTURE AND USE OF SUCH POLYMERS.

The present invention relates to a polyester type polymer, a manufacturing process and its use for the manufacture of articles.

It relates more particularly to a polyester of high molecular weight and viscosity in the molten state allowing use of this polymer in the processes for manufacturing articles by extrusion and pultrusion, for example or more generally the shaping processes require a polymer having a high melt viscosity to avoid or limit deformation of the shaped article before solidification of the material.

Polyesters, that is to say the polymers obtained by reaction between two monomers leading to ester functions are among the most used polymers.

Among these, polyethylene terephthalate is the most common and is the raw material for the manufacture of numerous articles such as films, threads, articles obtained by injection molding and / or blow molding.

These polyesters are more and more used because they combine interesting physical, physicochemical properties, high processability and are also entirely recyclable either by remelting or by depolymerization into starting monomers.

Many processes for the preparation of these polymers have been proposed for several decades.

Generally, these methods consist of a first step of esterification or transesterification by reaction of a diol with a diacid or a diester, followed by a second step of polymerization or polycondensation with elimination of alcohol.

These reactions are carried out in a molten medium, under atmospheric pressure or reduced pressure.

In such processes, the accessible degree of polymerization of the polymer is limited by the parasitic and concurrent degradation or depolymerization reactions occurring when the temperature is above 260 ° C. In addition, the manufacture of polymer with a high degree of polymerization, therefore with a high melt viscosity, is impossible because the stirring of the reactor becomes impossible as well as the casting of the polymer. Thus, it will be difficult to obtain polyethyleneterephthalates with an intrinsic viscosity index greater than 0.70. To achieve higher degrees of polymerization, it is proposed to carry out a post-condensation in the solid phase, consisting in maintaining the polymer in the solid state at a temperature between 200 ° C. and 240 ° C. and entraining the alcohol. formed by a advantageously non-oxidizing gaseous fluid or carrying out the polycondensation under reduced pressure.

With such a process, the degree of polymerization can be raised up to a certain limit corresponding to viscosity indices of the order of 1.4 dl / g, (absolute molecular weight by mass of the order of 80,000). .

The polymers thus obtained, however, have a viscosity in the molten state which is still too low to allow their use in shaping processes such as extrusion or pultrusion of articles with thick walls which do not allow the material to harden. immediately after leaving the die and therefore requiring the use of a self-supporting material which does not flow or very weakly in the molten state.

To obtain melt viscosity levels suitable for such processes, it has been proposed to add chain extenders and / or fillers to the polymers.

However, such solutions cannot meet all needs because they alter certain advantageous properties of polyester such as, for example, transparency, recyclability.

One of the aims of the present invention is to remedy these drawbacks by providing a polyester free from chain extender and having a sufficiently high degree of polymerization to obtain a level of viscosity in the molten state compatible with the shaping processes. articles, especially articles with thick walls.

To this end, the invention provides a polymer comprising repeating units of general formula I

In which :

R ₁ is an aromatic group which can comprise several nuclei in condensed form, and which can be substituted.

R ₂ is a linear or branched aliphatic hydrocarbon group comprising from 2 to 6 carbon atoms. According to the invention, the polymer has an absolute average molecular weight by mass Mw greater than 130,000, preferably greater than 135,000.

According to another preferred characteristic of the invention, the polymer has an absolute average molecular weight in number Mn greater than 45,000, preferably greater than 50,000. The absolute average molecular weights by mass and number Mw and Mn for the polyesters in accordance with the invention are determined according to the method described below.

This method uses GPC (gel permeation chromatography) or SEC (size exclusion chromatography) techniques. It corresponds to that described by Klaus Weisskopf (Journal of Polymer Science: part A, vol 26, 1919-1935; 1988).

However, the method used differs in the composition of the vector mixture. The mixture used consists of 95% by volume of CH ₂ CI ₂ and 5% by volume of HFIP (hexafluoroisopropanol) to which 0.005 mole of BF ₄ NBu _{4 is added} to eliminate any artifacts observed with certain polyesters.

The polyesters are dissolved in a mixture 75% by volume CH ₂ CI ₂ and 25% by volume of HFIP containing 0.005 mole of BF ₄ NBu ₄ .

The GPC is calibrated with polystyrene (PST) as the standard compound. The average molecular weights Mn, Mw, Mz and the polymolecularity index Ip are determined in PST equivalent.

The elution concentration is established by UV at 270 nm for injections of 40 μi at 2 mg - 3 mg / ml.

To determine the absolute means Mn, Mw, Mz and the real mass distributions, a secondary calibration is carried out with PST-2GT mixtures (polystyrene, polyethylene terephthalate) using as polyesters (2GT) model polyesters characterized by light scattering towards 1980 by Strazielle. The relation (II) connecting logM (PST) to absolute log M obtained is:

Log M absolute = 1.011752 log M PST - 0.292657 (II)

This relationship was used to calculate the absolute Mn and Mw from the Mn and Mw measured against the PST standard.

The experimental conditions of the analysis method are as follows:

- Columns: 3 Phenomenex Mixed ultra high-mass columns, (5μm precolumn). The diameter of the columns is 3/8 ", and the length of 60 cm

- Pump injector: Waters Alliance

- Detectors: RI ERMA refractometer sensitivity: 16 -UV: UV2000 TSP dual wavelength (270nm and 290nm)

- "Home made" viscometric coupling with capillary head loss and correction of flow effects. - Eluent: 95% by volume of DICHLOROMETHANE, 5% by volume of HFIP and 0.005 mole of BF ₄ NBu ₄

- Flow rate: 1 ml / min

- Concentration of solutions: 0.2% to 0.3% by weight. - Volume injected: 40μl

- Calibration: Polystyrene 100 to 4.10 ⁶ (- Quasi-linear from 10 ³ - 4.10. ⁶ )

- Calibration in [η] M PST

According to another preferred characteristic of the invention, the group R ₁ is chosen from the group comprising the divalent phenyl, naphthyl and sulfophenyl groups. The phenyl group is the preferred group and corresponds to the terephthalic and / or isophthalic acid monomers or their esters.

As for the group R ₂ , it is advantageously chosen from the group comprising the divalent ethyl, propyl and butyl groups. The ethyl group corresponding to the ethylene glycol monomer is the preferred group. Polyester having an absolute molecular weight by mass Mw greater than

130,000 has a melt viscosity greater than 8040 Pa.s.

This characteristic of viscosity in the molten state (Vf) cannot be measured directly and has been evaluated using correlation curves with respect to Mw. Thus, this relation is generally defined by the following relation (III): Vf = k * Mw ³ ' ⁴ (III)

The coefficient k determined experimentally is equal to 5.10 ^"14 According to another characteristic of the invention which is also an object of it, such a polymer of high degree of polymerization is capable of being obtained by a manufacturing process defined by the following steps: i) - Preparation of a prepolymer from the monomers corresponding to the production of a repeating unit according to general formula I, said prepolymer advantageously having a degree of polymerization at least equal to 10, preferably included between 10 and 80. ii) - Formation of particles of said prepolymer, having a surface area / mass ratio of polymer greater than 20 cm ² / g, advantageously greater than or equal to 50 cm ² / g, preferably greater than or equal to 80 cm ² / g. iii) - At least partial crystallization of said prepolymer particles, iv) - Carrying out of a solid phase polycondensation of the polymer until obtaining of a desired degree of polymerization. According to a preferred embodiment of the invention, the solid phase polycondensation is advantageously carried out by setting the particles in motion relative to one another by means of agitation, and heating the particles. at a temperature, advantageously the highest possible but lower than the temperature causing the polymer to melt on the surface of the particles. In addition, to improve the elimination of the alcohol and water produced by the polycondensation reaction, the bed of particles is swept or traversed by a fluid, preferably a non-oxidizing gaseous fluid such as nitrogen. To promote this elimination, it is also possible to carry out this polycondensation in the solid phase under reduced pressure.

Advantageously, the flow of gaseous fluid can cause the particles to move. In one case, the solid phase condensation can be carried out in a fluidized bed. However, as the polymer particles are crystallized, the risks of sticking are minimal allowing the use of a fixed bed of particles in this phase of polycondensation in the solid state.

According to another characteristic of the invention, the condensation temperature in solid phase is advantageously less than or equal to 270 ° C, preferably between 220 ° C and 270 ° C.

According to the invention, step i) of preparation of the prepolymer can be carried out by all known methods and in particular in the first steps of the usual method of manufacturing conventional polyesters.

These methods generally include:

- an esterification step,

- a prepolymerization step. Two routes are mainly used for carrying out this esterification step, in particular for the manufacture of polyethylene terephthalate.

The first route of production is the so-called "methyl terephthalate" (DMT) route. It is a transesterification reaction. The molten DMT is added to the excess ethylene glycol (EG), the EG / DMT molar ratio being approximately 1.9 to 2.2, and the reaction is carried out at atmospheric pressure and at temperatures of approximately 130 ° C. 250 ° C. It requires the presence of a catalyst, for example, manganese acetate. The methanol released by the reaction is removed by distillation. The excess ethylene glycol is removed after the transesterification reaction. The catalyst which is also a catalyst for the degradation of the polyester is blocked with phosphorous compounds after the reaction. The product resulting from the transesterification is a mixture of bis-hydroxyethyl terephthalate (BHET) and oligomers.

The second route is the so-called "direct esterification" route. It is an esterification reaction of terephthalic acid with ethylene glycol. It is carried out at temperatures from 130 ° C to 280 ° C. Ethylene glycol is present with an EG / Terephthalic Acid molar ratio of approximately 1 to 1.4. The result of this reaction is a mixture of oligomers having terminal acid and hydroxyethyl functions. The use of these methods is the subject of numerous studies described in the literature. The conditions indicated above do not constitute a limitation on the scope of the present invention.

The subsequent prepolymerization step is a polycondensation polymerization step. It is generally catalyzed using metallic compounds, for example by compounds of antimony, titanium or germanium. It can be catalyzed by any polycondensation catalyst described in the prior art.

This liquid phase prepolymerization step 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 molten phase dispersed in a liquid medium. The implementation of these two modes will be described later. The prepolymer obtained is advantageously of average degree of polymerization between 10 and 80, preferably between 20 and 80. By average degree of polymerization is meant the absolute average degree of polymerization defined by the following formula (IV):

où M₀ est la masse molaire du motif de répétition du polymère, Mj est la masse molaire de la chaîne de taille référencée i, et nj est le nombre de chaînes de taille référencée i. Les masses molaires sont les masses molaires absolues.

where M ₀ is the molar mass of the repeating unit of the polymer, Mj is the molar mass of the chain of size referenced i, and nj is the number of chains of size referenced i. The molar masses are the absolute molar masses.

The average degree of polymerization is related to the absolute molar mass in number M _n absolute, according to the above formula. The latter is evaluated by

Gel Permeation Chromatography (GPC) with viscosimetric coupling (see method described above). The viscosity in solution of the polymer is linked to the length of the chains and therefore to the number-average molar mass and to the average degree of polymerization. It is an indicator of the progress of the polymerization.

In this document, the term viscosity index (IV) is understood to mean, without indication to the contrary, the viscosity in ml / g measured at 25 ° C. using a Ubbelohde type viscometer 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. For PET, a correlation (V) between the viscosity index and the average degree of polymerization evaluated by GPC was established: DP _n = 1.19 * IV - 7 (V) in which IV is expressed in ml / g. This correlation is valid for viscosity indices between 10 and 70 ml / g and has been established experimentally.

The prepolymer thus obtained is ,. according to the invention, put in the form of particles of controlled dimensions to allow diffusion of the alcohol formed by the condensation reaction, without physical limitation. Thus, the particles formed have, according to the invention, a surface / mass ratio at least equal to 20 cm ² / g, preferably greater than or equal to 50 cm ² / g, advantageously greater than or equal to 80 cm ² / g.

The shape of the particles is not critical and depends on the technique used for the preparation thereof. Thus, for the techniques leading to an almost spherical shape of particles, the average size of these particles should be less than 1 mm, preferably less than 0.8 mm, advantageously between 50 μm and 0.5 mm. By particle size, it should be understood that all the particles suitable for the process of the invention must pass at least through a sieve whose orifices have a diameter of 1 mm, preferably less than 0.8 mm, advantageously less than 0.5 mm.

As a technique making it possible to obtain particles of almost spherical shape, mention may be made of sputtering, spherical atomization or atomization through pressurized nozzles. Another technique particularly suited to the production of spherical particles is prilling. This technique is described in an article "Prilling, process of choice for solid forms" published in the journal Informations Chimie n ° 389-June 1997. These techniques are implemented by feeding the prepolymer in the molten state in the means spraying or atomizing.

The prepolymer can also be formed into particles by grinding or flaking techniques, for example. With these techniques, the particles obtained can have a high form factor (ratio between the smallest dimension and the largest dimension of a particle). To allow diffusion of the diol and of the water formed without physical limitation, it is advantageous for the smallest dimension of these particles to be less than 700 μm, preferably less than or equal to 200 μm. The form factor of the particles is advantageously greater than 10.

It is also possible to form particles by dispersing the prepolymer in a liquid which will advantageously constitute the medium for carrying out polycondensation in the solid phase.

This liquid must not be a solvent for the alcohol formed or a plasticizer or swelling agent for the polymer.

In this latter embodiment, the prepolymer can be dispersed in the molten state in the liquid medium, solidification being obtained by cooling. However, it is also possible to disperse the product obtained after the esterification or transesterification step in the liquid medium. The liquid suspension of the particles of esterification or transesterification product is maintained at temperature to cause polycondensation and to obtain a degree of polymerization of the prepolymer particles equivalent to that of the prepolymer obtained by the polycondensation route in the molten state. The particles are then solidified by cooling.

Other methods of forming prepolymer particles can be used without departing from the scope of the invention. According to the process of the invention, the particles thus obtained are at least partially crystallized. In certain cases, this crystallization can be obtained by cooling and maintaining the particles at a temperature greater than or equal to 100 ° C., advantageously between 130 ° C. and 210 ° C. It intervenes mainly in the surface layer of the particle, thus making it possible to avoid the problems of sticking during the stage of condensation in solid phase.

The last step of the process is the realization of polycondensation in solid phase of the polymer in the form of particles.

This solid phase polycondensation, in the process of the invention, exhibits rapid kinetics and can be continued at high degrees of polymerization because of the particle size which removes the physical limits to the diffusion of the diol and of the volatile compounds formed. during the polycondensation reaction in the material, and to the characteristics of the starting prepolymer, in particular its degree of polymerization.

Solid phase polycondensation is carried out in a device similar to that used to carry out solid phase post-condensation in conventional polyester manufacturing processes. Thus, it is advantageously carried out by setting the particles in motion with a non-oxidizing gaseous fluid, thereby forming a fluidized bed.

As gaseous fluid suitable for the invention, non-oxidizing gases are preferred. Thus, nitrogen, rare gases, inert gases, CO ₂ are the preferred fluids, nitrogen being the preferred gas.

The particles are heated by any suitable means, in particular by supplying the hot gaseous fluid, to a temperature allowing advancement of the polycondensation, advantageously with kinetics acceptable for industrial exploitation. This temperature must be lower than the temperature at which a melting or an onset of melting of the polymer particles would occur, in particular on the surface thereof. This condition is necessary to avoid sticking of the particles together. In a preferred embodiment, this temperature increases with the advancement of the polycondensation reaction. This increase in temperature can be continuous or be carried out in successive stages.

Thus, the temperature at the start of solid phase polycondensation is advantageously greater than 220 ° C. and rises to values close to or equal to 270 ° C. at the end of polycondensation.

The duration of this polycondensation step is variable and depends on the degree of polymerization desired. It can vary from a few tens of minutes to a few tens of hours. Other process variants are possible for carrying out this polycondensation step in the solid phase.

Thus, the particles can be set in motion by mechanical means such as ultrasonic agitation, mechanical agitation. The gaseous fluid can also sweep the surface of the particle bed. It is also possible to carry out this polycondensation in the solid phase by using a liquid as a fluid. This embodiment is used in particular when the preparation of the prepolymer is carried out by the polycondensation process in dispersion in a liquid.

The polymer particles obtained at the outlet of the solid phase polycondensation step can be used as a raw material for the production of articles in processes for shaping these articles.

As the process of the invention makes it possible to obtain polymers of very high molecular weight, the polymer in the molten state has a high viscosity allowing its use in the shaping processes by extrusion, pultrusion of articles in particular with walls thick, that is to say articles of shapes and dimensions preventing any immediate cooling at the outlet of the die. For the manufacture of such articles, it is necessary that the material used does not immediately flow out of the die to avoid any deformation before solidification thereof.

As examples of articles which can be produced with such a polymer, mention may be made of profiles, tubes, pipes, plates of any shape.

Of course, the polymer with a high degree of polymerization can be used alone or in combination with additives usually used to improve or modify certain properties of the polymers such as thermal stability, resistance to UN radiation. or to light, fireproofing properties, resistance to oxidation. It is also possible to use the polymer with pigments and / or dyes as well as fillers or reinforcing fillers. By way of example, mention may be made, as filling fillers, of mineral powders such as clays, talc, silica, alumina and as reinforcing fillers for glass fibers, carbon fibers, ceramic fibers or thermosetting plastic fibers.

Other advantages, details of the invention will become more clearly apparent in the light of examples given only for information.

EXAMPLE 1

A poly (ethylene terephthalate) prepolymer with an initial viscosity index (IV) of 42 ml / g corresponding to an average degree of polymerization of 43 is prepared according to a conventional process of direct esterification and polycondensation in the melt phase, starting from 'purified terephthalic acid and ethylene glycol, in the presence of 250 ppm of catalyst based on antimony oxide (expressed by mass of Sb). This prepolymer contains 52 μeq of acid terminations per gram of prepolymer.

The prepolymer is solidified en masse and then ground in the presence of dry ice. The grinding product is sieved to select the particles passing through a 400 μm mesh sieve.

The sieved powder is dried for 3 hours at 130 ° C under vacuum.

The polymer thus obtained has a degree of crystallization of approximately 50%.

This powder is fed into a 250 ml flask placed on a rotary evaporator rotated at a speed of 30 revolutions per minute. Heating of the powder is obtained by an oil bath in which the flask is immersed.

A flow of nitrogen with a standardized flow rate of 25 to 30 l / h is fed into the tank.

The powder is brought to a temperature of 250 ° C., samples are taken at different treatment times to determine the progress of the polymerization.

This evolution is observed by measuring the absolute average molecular weights according to the technique described above.

The viscosity index IV expressed in dl / g has been determined by solubilization at room temperature (between 15 and 25 ° C) of the polymer in a solvent comprising 75% by volume of CH ₂ CI ₂ and 25% by volume of HFIP. The solvent is then evaporated to obtain a film which will be dissolved at a temperature of 110 ° C in a mixture of phenol / dichlorobenzene solvents (50/50). The viscosity index is measured from a solution comprising 0.5% by weight of polymer, according to the method indicated above. The viscosity in the molten state was calculated using the correlation formula ( III) indicated above.

Ip represents the polymolecularity index of the polymer. The results obtained are shown in Table 1 below.

Table -1-

Example 2:

Example 1 is repeated but carrying out the polycondensation in solid phase at a temperature of 240 ° C instead of 250 ° C and for 25 hours. The polymer obtained has the following properties:

Example 3:

Example 2 is repeated, but using as a prepolymer, a polyester with a degree of polymerization equal to 73 and 64 μeq of acid terminations per gram of prepolymer.

The polymer obtained after polycondensation in solid phase has the following properties:

Comparative example: Example 1 is repeated but using a prepolymer with a degree of polymerization equal to 43 in the form of particles obtained by grinding and not passing not through a mesh screen equal to 1 mm, but passing through a mesh screen equal to 2 mm.

After 18 hours of solid phase polycondensation, a polymer with an IV of 182. is obtained. Continuation of the polycondensation process leads to a reduction in the IV.

Claims

1- Polymer comprising recurring units of general formula I

in which: R ₁ is an aromatic group which can comprise several rings in condensed form, and which can be substituted, R ₂ is a linear or branched aliphatic hydrocarbon group comprising from 2 to 6 carbon atoms, characterized in that the absolute molecular weight by mass Mw is greater than or equal to 130,000. 2. Polymer according to claim 1, characterized in that it has an absolute molecular weight in number Mn greater than or equal to 45,000. 3. Polymer according to claim 1 or 2 characterized in that the absolute average molecular weight by mass Mw is greater than or equal to 135,000 and the absolute average molecular weight in number Mn greater than or equal to 50,000. 4. Polymer according to claim 1 or 2, characterized in that the group R ₁ is chosen from the group comprising the divalent phenyl, naphthyl, sulfophenyl groups. 5. Polymer according to one of the preceding claims, characterized in that the group R ₂ is chosen from the group comprising the ethyl, propyl and butyl groups. 6. Method for the manufacture of polymer according to one of claims 1 to 5, characterized in that it consists in: i) Preparing a prepolymer from the monomers corresponding to the obtaining of a repeating unit according to the general formula (l), ii) forming particles of said prepolymer, having a surface area / mass ratio of polymer greater than 20 cm ² / g. iϋ) At least partially crystallize said prepolymer particles. iv) Carry out a solid phase polycondensation of the polymer until a polymer having an absolute average molecular weight by mass Mw greater than 130,000 is obtained. 7. Process. according to claim 6, characterized in that the polycondensation in solid phase is carried out under reduced pressure. ^'8. A method according to claim 6, characterized in that the solid phase polycondensation is carried out in the presence of a non-oxidizing gaseous fluid. 9. Method according to claim 8, characterized in that the gaseous fluid is chosen from the group comprising nitrogen, rare gases, inert gases, CO ₂ . 10. Method according to one of claims 6 to 9, characterized in that step ii) of particle formation consists in carrying out an atomization or a spraying of the molten prepolymer. 11. Method according to one of claims 6 to 9, characterized in that step ii) of particle formation consists in carrying out a prilling of the molten prepolymer. 12. Method according to one of claims 6 to 9, characterized in that step ii) of particle formation consists in forming a powder by cutting and grinding the prepolymer in the solid state. 13. Method according to one of claims 6 to 12, characterized in that the particles obtained in step ii) have a surface area to mass ratio of polymer greater than or equal to 50 cm / g. 14. Method according to one of claims 6 to 13, characterized in that the at least partial crystallization of the particles is obtained by cooling to a temperature above 100 ° C. 15. Method according to one of claims 6 to 14, characterized in that step i) of preparation of a prepolymer is carried out in a molten medium. 16. Method according to one of claims 6 to 15, characterized in that step i) of preparation of a prepolymer is carried out by a suspension polymerization process, the particles being formed during the polymerization step . 17. Method according to one of claims 6 to 16, characterized in that said prepolymer has a degree of polymerization at least equal to 10. 18. Method according to ^" claim 17, characterized in that said prepolymer has a degree of polymerization between 10 and 80. 19. Use of the polymer according to one of claims 1 to 5 for the shaping of articles with thick walls. 20. Use of the polymer according to one of claims 1 to 5 for the manufacture of compositions comprising filling fillers, reinforcing fillers, and the manufacture of articles by shaping these compositions. 21. Use according to claim 19 or 20 characterized in that the shaping is obtained by extrusion or pultrusion processes.