PROCESS FOR THE PREPARATION OF AN OLIGOMER FLAME-RETARDING ADDITIVE AND ITS USE FOR ENDOWING A LINEAR POLYESTER WITH SELF-EXTINGUISHING CHARACTERISTICS

Abstract: An oligomer flame-retarding additive can be defined by the general formula wherein: R is the hydrogen atom, or a linear or branched alkyl radical, containing from 1 to 6 carbon atoms; m takes the value 1, 2 or 3; n takes a value, or an average value, comprised within the range of from 2 to 50. Such an additive is obtained by means of the oligomerization of a hydroxyalkylenephenylphosphinic acid or of a related alkyl ester thereof. According to another form of practical embodiment, the flame-retarding additive is the product of co-oligomerization of a hydroxyalkylenephenylphosphinic acid, or of a related alkyl ester thereof, with a phenylphosphonic acid or a related alkyl ester thereof. Such oligomer additives are used for endowing a linear polyester with self-extinguishing characteristics.

Description: The Present invention relates to an oligomer flame-­ retarding additive, to the process for its preparation and to its use for endowing a linear polyester with self-­ extinguishing characteristics. It is known that the linear polyesters are obtained in the art by polycondensing, in the presence of suitable catalysts, bicarboxy aromatic acids with alkylene glycols, and, in particular, terephthalic acid, or a di­ methyl ester thereof, with ethylene glycol. The so obtained linear polyesters are valuable products, in that they constitute starting materials for such interesting manufactured articles are fibres, films, sheets and other articles. A drawback of these articles is their flammability, with all of the consequent risks, in particular in the textile sector and in the electrotechnical sector. Hence, various flame-retarding agents have been proposed for application to the linear polyester by a surface treatment, or by the addition during the processing step, e.g., during the spinning step. Thus, for example, tris-dibromopropyl phosphate has been used in the textile sector as a finishing agent. But its resistance to washings is not completely satisfactory, and it shows, furthermore, a certain toxicity. The addition of brominated flame-retarding agents during the spinning step is furthermore known. However, difficulties exist in finding brominated compounds which are stable and free from phenomena of decomposition under the temperature conditions typical of the spinning process, and of the other fibre-proces­ sing steps. Representative of the prior art is EP-A-0 092 868, published Jan.22, 1986, which discloses a flame-­ retarding polyester composed of units deriving from an aromatic bicarboxylic acid and an alkylene glycol, and, optionally, units deriving from a phosphorus compound in such an amount as to contribute from 0,4% to 0,8% of elemental P of the weight of the entire composition. Such a polymer is prepared by adding the phosphorus compound to a precondensate of the carboxylic acid and the glycol concerned, and carrying then out the polycondensation. The P-compound is a hydroxymethylphenylphosphinic acid, which may undergo a partial condensation with the attendant formation of oligomers: the hydroxymethyl­ phenylphosphinic acid in question tends to polycondense when heated, with loss of water, and its esters, still on heating, tend to transesterify with loss of alcohol, a behaviour which clearly derives from the bifunctional nature of such compounds. However, EP-A-0 092 868 does not teach the use of such oligomers as flame retarders, but, contrarywise, it suggests to convert such oligomers into the relative monomer, and, moreover, the P-compound is added preli­ minarily to the polycondensation stage of the bicarbo­ xylic acid and the glycol. The addition of the phosphorous monomers causes a drop in the viscosity of the polyester with attendant worsening of its properties, so that processes such as spinning become virtually impossible. The present invention, therefore, teaches to use, for retarding flame in linear polyesters, an additive having P-containing repeating units, of the general formula: wherein Φis selected from among: - unsubstituted phenyl; - phenyls substituted with one or more substituents selected from among (C1-C4) alkyls, (C1-C4) alkoxies, and halogens, particularly C1 and Br; - unsubstituted naphthyl, - naphthyls substituted with one or more substituents selected from among (C1-C4) alkyls, (C1-C4) alkoxies and halogens, particularly C1 and Br, and - (C1-C4)alkyls; and wherein: R is a hydrogen atom, or a linear or branched alkyl radical, containing 1 to 6 carbon atoms; m takes the value 1, 2 or 3; n takes a value, or average value, comprised within the range of from 2 to 50. Preferably, in the general formula (I) R is a hydrogen atom, m is 1, and n is from 20 to 80. The invention, moreover, teaches to prepare the flame-­ retarding additive of formula (I) by a process compris­ ing the steps of heating a hydroxyalkylenephenylphos­ phinic acid, or an alkyl ester thereof, as defined by the formula: wherein Φ, R and m have the same meanings as defined in claim 1, to a temperature of from, 140°C to 180°C and under a pressure of from 0,1 hPa to 200 hPa (0,1-200 mmHg), and removing the as-formed water or the aliphatic alcohol, respectively. In case R in the above formula (II) is the hydrogen atom, the reaction can be carried out in the presence of such a solvent as xylene, for the purpose of removing water as an azeotropic mixture during the course of the condensation. Also small amounts of catalysts can be used, which favour the oligomerization of the hydroxyalkylenephenyl­ phosphinic acid or ester, such as, e.g., tin, germanium, titanium, manganese, magnesium and zinc compounds. The alkali metal alkoxides, e.g., sodium alkoxide, are efficacious in the oligomerization of hydroxyalkylenephe­ nylphosphinic acid. The oligomerization time is the time required for obtaining the desired value for n in above formula (I). Under the above indicated conditions, the reaction time can generally vary within the range of from 1 to 5 hours. According to another form of practical embodiment of the present invention, the flame-retarding additive is the product of co-oligomerization of a hydroxyalkylene­ phenylphosphinic acid, or of a related alkyl ester there­ of, having the above formula (II), with a phenylphospho­ nic acid or a related alkyl ester thereof, which can be defined by the general formula: wherein: R₁ an R₂ are equal to, or different from, each other, and each of them represents a hydrogen atom, or a linear or branched alkyl radical, containing from 1 to 6 carbon atoms. In the preferred form of practical embodiment, the hydroxyalkylenephenylphosphinic acid (II), in which R represents the hydrogen atom, and m is 1, is co-oligomer­ ized with the phenylphosphonic acid (III) wherein both R₁ and R₂ represent the hydrogen atom. Said co-oligomerization is carried out within the general range of oligomerization conditions as reported above, and yields similar products. The oligomer flame-retarding agent so obtained can be added to the prepolymer of the linear polyester, during the polycondensation step. More particularly, in the preparation of the self-­ extinguishing linear polyester of the present invention, a low molecular weight pre-condensate is first formed, by starting from the aromatic bicarboxy acid, or from a related di-lower-alkyl ester thereof (generally, tereph­ thalic acid, or dimethyl terephthalate) and from the alkylene glycol (generally, ethylene glycol). To the precondensate, the suitable amount is then added of the oligomer flame-retarding additive, and finally the polycondensation is carried out until the values of molecular weight typical for linear polyesters are reached. Typically, said polycondensation is carried out at 270-280°C with pressure being reduced down to values of the order of 0.1333 hPa (0.1 torr) or less. According to another form of practical embodiment of the present invention, the oligomer flame-retarding additive is added to the linear polyester in the molten state (270°-290°C), and is homogenized with it. In particular, the addition can be carried out at the end of the polycondensation step, before the linear polyester is transformed into granules, or it can take place immediately before the spinning step. According to a further form of practical embodiment of the present invention, a composition (master) is prepared of the linear polyester, which contains a high amount of oligomer flame-retarding additive, e.g., up to about 20-30% by weight. This composition, which can be obtained both by means of the procedure of copolymerization of the oligomer additive with the prepolymer of the linear polyester, and by means of the blending and homogenization of the additive with the molten linear polyester, is added in its turn to the linear polyester for supplying the desired self-­ extinguishing characteristics. It should be observed that in any case self-extinguishing linear polyesters are obtained, wherein the phosphorus compound is chemically bonded and evenly distributed throughout the macromolecular chain. The oligomer flame-retarding additives of the present invention are products which show a softening temperature which is a function of their molecular weight, and are storage-stable and easily-handled products. The self-extinguishing linear polyesters of the present invention contain an amount of phosphors (as expressed as the element) which can vary within the range of from 0.5 to 0.8% by weight, and is preferably of the order of from 0.5 to 0.65% by weight. In the above disclosure, oligomer compounds and co-­ oligomer compounds of hydroxylkylenephenylphosphinic acid, or of a related alkyl ester thereof, have been disclosed. However, the fact should be appreciated that similar oligomer or co-oligomer compounds can be obtained from such an acid, or related ester, in which the phenyl group is substituted by a group selected from: - phenyl substituted with one or more substituents from the group of (C₁-C₄)-alkyl, (C₁-C₄)-alkoxy, or halogen, in particular chlorine and bromine, substituents; - naphthyl; - naphthyl substituted with one or more substituents from the group of (C₁-C₄)-alkyl, (C₁-C₄)-alkoxy, or halogen, in particular chlorine and bromine, substituents; - (C₁-C₄)-alkyl. Furthermore, the flame-retardant agents of the present invention can be used in polyesters different from polyethyleneterephthalate, e.g., polybutylenetereph­ thalate. The following experimental examples are illustrative and non-limitative of the present invention. Example 1 172 g (1 mol) of hydroxymethylphenylphosphinic acid is heated at 150°C inside a glass reactor of 500 ml of capacity, operating under a pressure of 66.65 hPa (50 mmH), and water which evolves in vapour form is collected inside a cooled trap. After 5 hours, 9 g (0.5 mol) of water is collected, and the condensation rate decreases considerably. The reaction mass is cooled, and 160.5 g of a solid product is recovered. The 31 P-N.M.R. analysis of the product dissolved in DMSO (dimethylsulphoxide), evidences the presence of the following molecular species: Such a product can be represented in its whole by the general formula wherein: n has the average value of 2. Example 2 172 g (1 mol) of hydroxymethylphenylphosphinic acid is heated at 180°C inside a glass reactor of 500 ml of capacity, operating under a pressure of 0.133 hPa (0.1 mmH). After 4 hours, 14.5 g (0.80 mol) of water is collected. The reaction mass is cooled, and a solid product is recovered, which, at 31 P-N.M.R. analysis shows the presence of a low percentage of monomer (<5%) and can be represented by the formula (IV) in Example 1, with an average value of n of about 5, The equivalent weight of this product, as determined by titration with sodium, is of about 720. Example 3 100 g (0,50 mol) of isobutyl ester of hydroxymethyl­ phenylphosphinic acid is heated at 180°C, under a high vacuum, together with 0.5 g of dibutyltin dilaurate. After 3 hours, during which isobutyl alcohol is removed, 70 g is recovered of a solid soluble in dimethylsulphox­ ide. The 31 P-N.M.R. analysis of the product evidences the oligomer nature of this product, which can be represented by the formula: with an average value of n equal to about 35. Example 4 172 g (1 mol) of hydroxymethylphenylphosphinic acid is heated at 150°C together with 158 g (1 mol) of phenyl­ phosphonic acid on 250 ml of xylene. After 3 hours of reaction, during which approximately 8.5 g of water is removed, xylene is separated and about 300 g of a high-­ viscosity product is recovered. The 31 P-N.M.R. analysis of the product dissolved in dimethylsulphoxide (DMSO) evidences the presence of the following molecular species: higher molecular weight products: negligible The average degree of co-oligomerization is there­ fore equal to about 2. Example 5 To an autoclave, 1 part by weight (pbw) of ethylene glycol and 1.8 pbw pf terephthalic acid are charged. The mixture is heated to the temperature of 235°C, under a pressure of 196.132 hPa 2 kg/cm², and the reaction is carried out in the presence of 0,03% by weight (relatively to terephthalic acid ) of a quaternary aminic base, until a precondensate is obtained, which has an average molecular weight of approximately 500. This precondensate is used in the following experimental examples. Example 6 To an autoclave, 150 pbw of the precondensate of Example 5, 4.7 pbw of the product of oligomerization of hydroxymethylphenylphosphinic acid (obtained according to Example 1) is charged, together with 0.04% by weight (relatively to precondensate) of H₃PO₄ and Sb₂O₃. The mass is heated at 170-280°C, and during a time of 1.5 hours the pressure is decreased from 1013,23 hPa (760 torr) to less than 1,332 hPa (10. torr). The reaction is made proceed under vacum for a further 2 hours, and at the end of this time period, a linear polyester is obtained, which has the following characteristics: Example 7 150 pbw of the precondensate of Example 5, to which 0.04% by weight of H₃PO₄ and GeO₂ is added, is charged to an autoclave. The mass is heated to 270-280°C with stirring, and the pressure is reduced from 1013,23 hPa (760 torr) to less than 1,332 hPa (1.0 torr) within a time of 1.5 hours. The reaction is allowed to proceed under vacuum or a further time of approximately 80 minutes and 4.5 pbw is then added of the product of oligomerization of hydroxymethylphenylphosphinic acid (obtained according to Example 3). The reaction is made proceed for a further 60 minutes, under the conditions of temperature and pressure as indicated above, and a linear polyester is obtained, which has the following characteristics: Example 8 150 pbw of the precondensate of Example 6, containing 0.04% by weight of H₃PO₄ and Sb₂O₃ is charged to an autoclave. The mass is heated at 270-280°C and the pressure is reduced from 1013,23hPa (760 torr)to less than 1,332 hPa (1 torr) during a time of 1.5 hours. The reaction is made proceed for a further 2 hours, and a linear polyester is obtained, which has the following characteristics: The granules of the so-prepared polyester are blended with 3.5% by weight of the product of oligomerization of hydroxymethylphenylphosphinic acid (obtained according to Example 3). The blend is melted under an inert atmosphere for 35 minutes at 280°C and is then kept under a pressure lower than 1,332 hPa (1 torr) for the subsequent 30 minutes. Thus, a linear polyester is obtained, which has the following characteristics: Example 9 A master of linear polyester is prepared, which contains 30% by weight of the oligomerization product obtained in Example 3. This master is obtained by means of a copolymerization procedure similar to that of above Examples 6 and 7. A further master is obtained, with a composition similar to the preceding one, by blending the product of oligomerization obtained in Example 3 with the pre-formed linear polyester and heating the blend under a high vacuum for 2 hours at 280°C, analogously to the preceding Example 8. The so-obtained masters are added to the linear polyester during the spinning step, in such an amount as to give the fibre a phosphorus content (expressed as the element) of 0.6% by weight. In this way, fibres of linear polyester are obtained, which have a LOI value higher than 30.

Claims: Claims for: BE, CH, DE, FR, GB, LI, LU, NL, SE 1. Use for retarding flame in linear polyesters, of an additive having P-containing repeating units, of the general formula: wherein Φ is selected from among: - unsubstituted phenyl; - phenyls substituted with one or more substituents selected from among (C1-C4) alkyls, (C1-C4) alkoxies, and halogens, particularly C1 and Br; - unsubstituted naphthyl, - naphthyls substituted with one or more substituents selected from among (C1-C4) alkyls, (C1-C4) alkoxies and halogens, particularly C1 and Br, and - (C1-C4) alkyls and wherein: R is a hydrogen atom, or a linear or branched alkyl radical, containing 1 to 6 carbon atoms; m takes the value 1, 2 or 3; n takes a value, or average value, comprised within the range of from 2 to 50. 2. Use of the flame-retarding additive according to claim 1, wherein R is a hydrogen atom, m is 1, and n is from 20 to 50. 3. Process for preparing the flame-retarding additive to be used according to claim 1, comprising the steps of heating a hydroxyalkylenephenylphosphinic acid, or an alkyl ester thereof, as defined by the formula: wherein Φ, R and m have the same meanings as defined in claim 1, to a temperature of from 140°C to 180°C and under a pressure of from 0,1 hPa to 200 hPa (0,1-200 mmHg), and removing the as-formed water or the aliphatic alcohol, respectively. 4. Process according to claim 3, wherein R is a hydrogen atom and the reaction is carried out within a solvent capable of forming an azeotropic mixture with water. 5. Process according to claim 3, wherein the reaction is carried out in the presence of a catalyst selected from among the compounds of tin, germanium, titanium, zinc, manganese and magnesium. 6. Process according to claim 3, wherein R is a hydrogen atom and the reaction is carried out in the presence of an alkali metal alkoxide as the catalyst. 7. Use for retarding flame in linear polyesters of an additive having P-containing repeating units and obtained by co-polymerizing a hydroxyalkylenephenylphosphinic acid, or an alkyl ester thereof, as defined by formula (II), with a phenylphosphonic acid, or an alkyl ester thereof, having the formula: wherein R₁ and R₂ are equal to, or different from, one another, each of them being a hydrogen atom, or a linear or a branched (C1 -C6) alkyl. 8. Process for endowing a linear polyester with flame-­ extinguishing properties, wherein a flame retarding additive as defined in claims 1, 2 or 7 is added to the linear polyester concerned during the polycondensation step. 9. Process for endowing a linear polyester with flame-­ extinguishing properties, wherein a flame-retarding additive as defined in claims 1, 2 and 7 is added to the already pre-formed and molten linear polyester concerned. 10. Process for endowing a linear polyester with flame-extinguishing properties, according to claim 9, wherein to the molten linear polyester concerned a master-batch is added, containing the linear polyester and an amount of up to from 20% to 30% by weight of the master batch of a flame retarding additive as defined in claims 1, 2 and 7. 11. Process according to claims 8, 9 and 10, wherein the amount of the flame retarding additive is such as to supply to the self-extinguishing linear polyester an amount of elemental phosphorus of from 0,5% to 0,8% by weight, preferably from 0,5% to 0, 65% by weight of said linear polyester. Claims for the contracting states AT, GR, ES 1. Process for preparing a flame-retarding additive for linear polyesters, having P-containing repeating units of the general formula: wherein Φ is selected from among: - unsubstituted phenyl; - phenyls substituted with one or more substituents selected from among (C1-C4 alkyls), (C1-C4) alkoxies, and halogens, particularly C1 and Br; - unsubstituted naphthyl; - naphthyls substituted with one or more substituents selected from among (C1-C4) alkyls, (C1-C4) alkoxies and halogens, particularly C1 and Br, and - (C1-C4) alkyls, and wherein - R is a hydrogen atom, or a linear or branched alkyl radical, containing 1 to 6 carbon atoms; - m takes the value 1, 2 or 3; - n takes a value, or average value, comprised within the range of from 2 to 50, comprising the steps of heating a hydroxyalkylenephenylphosphinic acid, or an alkyl ester thereof, as defined by the formula: wherein Φ, R and m have the above defined values, to a temperature of from 140°C to 180°C, and under a pressure of from 0,1 hPa to 200 hPa (0,1-200 mmHg), and removing the as-formed water, or the aliphatic alcohol, respectively 2. Process according to claim 1, characterized in that R is a hydrogen atom, m is 1, and n is from 20 to 50. 3. Prrocess according to claim 1, characterized in that R is a hydrogen atom and the reaction is carried out within a solvent capable of forming an azeotropic mixture with water. 4. Process according to claim 1, characterized in that the reaction is carried out in the presence of a catalyst selected from among the compounds of tin, germanium, titahinium, zinc, manganese and magnesium. 5. Process according to claim 1, characterized in that R is a hydrogen atom and the reaction is carried out in the presence of an alkali metal alkoxide as the catalyst. 6. Process for preparing a flame-retarding additive having P-containing repeating units for linear polyesters, characterized in that it comprises the step of co-polymerizing a hydroxyalkylenephenylphosphinic acid, or an alkyl ester thereof, as defined in formula (II) in claim 1 with a phenylphosphonic acid, or an alkyl ester thereof, having the formula: wherein R₁ and R₂ are equal to, or different from, one another, each of them being a hydrogen atom, or a linear or a branched (C1-C6) alkyl. 7. Process for endowing a linear polyester with flame-extinguishing properties, characterized in that it comprises the step of adding a flame-retarding additive as obtained in claims 1, 2 or 6, to the linear polyester concerned during the polycondensation step. 8. Process for endowing a linear polyester with flame-extinguishing properties, characterized in that it comprises the step of adding a flame-retarding additive as obtained in claims 1, 2 and 6 to the already preformed and molten linear polyester concerned. 9. Process for endowing a linear polyester with flame-extinguishing properties, according to claim 8, characterized in that it comprises the step of adding a master-batch containing the linear polyester and an amount of up to from 20% to 30% by weight of the master batch of a flame-retarding additive as obtained in claims 1, 2 and 6. 10. Process according to claims 7, 8 and 9, characterized in that the amount of flame-retarding additive is such as to supply to the self-extinguishing linear polyester an amount of elemental phosphorus of from 0,5% to 0,8% by weight, preferably from 0,5% to 0,65% by weight of said linear polyester.

Inventors: CIPRIANI, GIOACCHINO, MARIANO, ARMANDO
Applicants: ENICHEM SYNTHESIS S.P.A.
Application year: 1987
Main classification: C07F9
IPC codes: C08L67, C07F9, D06M13, C08G63, C08K5, C09K21