PROCESS FOR THE PREPARATION OF IMIDIZED ACRYLIC POLYMERS

Abstract: Imidized acrylic polymers obtained by means of the reaction of an acrylic resin in the molten state, with at least one modifying agent having the general formula: R-X-NH-R′ (I) wherein: R and R′ are either equal to or different from each other and represent hydrogen or an alkyl, cycloalkyl, aryl or alkylaryl radical containing from 1 to 20 carbon atoms, and X is a bifunctional radical selected from the group consisting of: -CO-, -CONH-, -NHCO-, -OCO-, -SO₂, -C₆H₄SO₂-.

Description: The present invention relates to a process for preparing imidized acrylic polymers. The term "acrylic polymers" or "acrylic resins", as used in the present disclosure, and in the appended claims, is defined as homopolymers and copolymers and mixtures thereof, of alkyl esters of methacrylic or acrylic acid, wherein the alkyl group contains from 1 to 8 carbon atoms. Examples of esters of methacrylic acid or acrylic acid are methyl methacrylate, ethyl methacrylate, isopropyl methacrylate, sec.-butyl methacrylate, tert.-butyl methacrylate, methyl, ethyl, butyl and isopropyl acrylate. The acrylic polymers or acrylic resins can contain units derived from other ethylenically unsaturated monomers, such as styrene, α-methyl-styrene, acrylonitrile, acrylamide or from monomers having two ethylenic unsaturations such as, for example, butadiene. Preferably, the polymers prepared according to the invention have, furthermore, intrinsic viscosity values, determined in tetrahydrofuran (THF) at 30°C, of from 0.01 to 7 dl/g, particularly of from 0.2 to 2 dl/g. Imidized acrylic polymers are known. Such polymers however, possess a rather low glass transition temperature (Tg) which significantly limits their use. From the disclosures of US-A- 3 284 425 and GB-A- 926 629, it is known to increase the Tg of these polymers by imidization, achieved by means of reaction with ammonium hydroxide, ammonium phosphate or alkyl-amines, or by means of the partial reaction of the same acrylic resin with ammonium hydroxide, followed by the reaction with an alkylamine. Such processes show several drawbacks: in fact, the processes are carried out in an autoclave, are of the batch type, require heating and reaction times which are generally very long, and require the use of dissolving or suspending solvents. In order to overcome these drawbacks, in DE-C-1 077 872 a process was proposed for the preparation of imidized acrylic polymers in an extruder by using ammonium hydroxide in an aqueous phase. The product obtained however, has a poor thermal stability, and requires further treatments before it can be used in transformation processes. In US-A- 4 246 374 a process is disclosed for the preparation of acrylic polymers imidized in an extruder by means of direct reaction of the acrylic resin with ammonia or a primary amine under substantially anhydrous conditions. The product obtained shows good thermal stability, but the process conditions for preparing the product are particularly burdensome. For example, the process is carried out at temperatures of up to 450°C, and pressures of up to 100 MPa. The applicant has now found, and this is the object of the present invention, that the above-mentioned drawbacks can be overcome by preparing imidized acrylic polymers by means of the reaction of an acrylic resin with at least one modifying agent having the general formula: R-X-NH-R' (I) wherein: R and R' are either equal to or different from each other and represent hydrogen or an alkyl, cycloalkyl, aryl or alkylaryl radical containing from 1 to 20 carbon atoms, and X is a bifunctional radical selected from -CO-, -CONH, -NHCO-, -OCO-, -SO₂- and -C₆H₄SO₂-. In the case where R and R' differ, the former can contain heteroatoms such as halogens. Examples of modifying agents having the general formula (I) are acetamide, anisamide, benzamide, acetanilide, butyramide, benzanilide, propionamide, formamide, N-methyl-acetamide, N-methyl-benzamide, N-methyl-formamide, N-phenyl formamide, benzenesulphamide, ethyl carbamate, benzhydrazide, chloropropionamide and N,N'-dimethylurea. The imidized acrylic polymers obtained by means of the process of the present invention preferably have an optimum thermal stability and an intrinsic viscosity in tetrahydrofuran (THF) at 30°C comprised within the range of from 0.01 to 7 dl/g, and particularly from 0.2 to 2 dl/g, a nitrogen content comprised within the range of from 0.1 to 9% by weight, particularly of from 0.5 to 7% by weight, and a content of imidic units of at least 5% relative to the theoretical maximum value. On the basis of I.R. analysis, it is deduced that these imidic units are cyclic, even if such a structure is not binding for the purposes of the invention. A preferred method for preparing the imidized acrylic polymers according to the present invention comprises reacting an acrylic resin and the modifying agent of formula (I) under ambient pressure, or preferably, under a pressure lower than ambient pressure and at a temperature higher than the melting temperature of the acrylic resin. Preferred reaction pressures range from 0.1 MPa to 1.3 x 10⁻³ kPa (760 to 10⁻² torr), particularly from 0.065 MPa to 1.3 x 10⁻² kPa (500 to 0.1 torr). Most preferred is a pressure of 0.098 MPa (750 torr). Preferred reaction temperatures range from 200 to 350°C, particularly from 220 to 280°C, which are the most commonly used temperatures. The modifying agent is used in preferred amounts of from 5 to 60 mol percent, and particularly of from 10 to 50 mol percent, relative to the acrylic monomer unit. According to another preferred form and a practical embodiment of the process of the present invention, the reaction between the acrylic resin and the modifying agent having formula (I) is carried out in the presence of basic catalysts, acidic catalysts and/or transesterification catalysts. Such catalysts are high-boiling products which are stable under the reaction conditions; they can be preferably selected from the group consisting of tertiary amines, such as dicyclohexyl-amine, 1,1,3,3-tetramethyl-guanidine, 1,3-diphenyl-guanidine, quinoline, isoquinoline, 4-benzylpyridine, 4-phenylpyridine, 2,3-benzodiazine, 1,4-benzodiazine, 1-benzazine, 1,3-benzodiazine, N,N'-dicyclohexyl-carbodiimide, 2,2'-bipyridyl, 2,3'-bipyridyl, 2,4'-bipyridyl or such a catalyst can be selected from the group consisting of HCl, Sb₂O₃, Ti(OC₄H₉)₄, NaNH₂, SnO₂, potassium or sodium alkoxides, manganese acetate. The catalysts can be used in amounts which can be as high as 30% by weight, relative to the total amount of the reaction mixture. According to a further preferred form of a practical embodiment of the process of the present invention, the reaction between the acrylic resin and the modifying agent, having the general formula (I), can also be carried out in an extruder, in a mixer, or in similar apparatus suitably equipped with degassing devices. The process of the present invention can be carried out by using the acrylic resin both in the molten state and dissolved in a suitable solvent. The imidized acrylic polymers prepared according to the present invention can be processed by commonly used technologies for the transformation of thermoplastic polymers. Such processes include, for example, extrusion and injection-molding. The polymer can be used for the production of manufactured articles of any shapes and/or dimensions. Furthermore, such polymers can be used in the preparation of sheets, films, tubes and filaments. The imidized acrylic polymers obtained at the end of the process according to the present invention can be blended with suitable additives such as, for example, impact-resistant products, pigments, fibers, mineral fillers, flame retarding agents, stabilizers, lubricants and plasticizers. Foaming agents can be added to the polymers prepared according to the present invention, and the polymers can be used in the foamed form, possibly further blended with fibers and/or inorganic fillers in order to produce manufactured articles endowed with low density and high mechanical properties. The glass transition temperature (Tg) is determined by using a differential calorimeter, and this is the temperature corresponding to the point of the inflection in the temperature chart, when the heat capacity of the material changes. The temperature change rate is 20°C/minute, and the measurement is carried out by heating up to 200°C, with subsequent cooling. In order to better understand the present invention the following illustrative examples are presented. Example 1 To a glass reactor, equipped with stirrer and vent port for the volatile components, 25 g of a copolymer containing 98% by weight of methyl methacrylate and 2% by weight of methyl acrylate, having an intrinsic viscosity in THF at 30°C of 0.34 dl/g; and 15 g of benzamide are simultaneously charged under a nitrogen atmosphere. The reaction mixture is gradually heated to the melting temperature, and then to 255°C. The volatile reaction products are distilled off and removed. The reaction mixture is maintained at 255°C for approximately 3 hours, then the reactor is evacuated by a mechanical pump for 15 minutes. The reaction mixture is cooled to 150°C and refluxed with nitrogen; the reaction product is diluted with 50 ml of N,N'-dimethylformamide, to obtain a solution from which the polymer is recovered by coagulation with methanol. The product polymer is filtered, washed with ether and vacuum-dried. The polymer has an intrinsic viscosity in THF of 0.3 dl/g, a nitrogen content of 3.7% by weight, and a glass transition temperature (Tg) = 155°C. Furthermore, the polymer, according to thermogravimetric analysis (TGA) carried out by subjecting the sample to a temperature increase rate of 10°C/minute under a nitrogen atmosphere, shows a weight loss of 0.45% within the temperature range of from 50 to 300°C. The I.R. spectroscopy, carried out on the product, showed absorption bands at 1,698 cm⁻¹ and at 3,240 cm⁻¹, which could be presumably attributed to a cyclic imidic structure of the type: Example 2 The reaction is carried out according to the procedure of Example 1, except 0.2 ml of 4-benzyl-pyridine is added to the reaction mixture simultaneously with benzamide and the copolymer. The product polymer has an intrinsic viscosity in THF of 0.28 dl/g, a nitrogen content of 2.9% by weight, and a Tg = 160°C. Example 3 The reaction is carried out according to the procedure of Example 1, but 8 ml of 4-benzyl-pyridine are added simultaneously with benzamide and the copolymer, and the reaction is carried out at 230°C. The product polymer has an intrinsic viscosity in THF of 0.28 dl/g, a nitrogen content of 6.2% by weight, and a Tg = 183°C. Example 4 The reaction is carried out according to the procedure of Example 1, with benzamide being replaced with 18 g of anisamide, and the reaction being carried out at 280°C. The product polymer has an intrinsic viscosity of 0.29 dl/g, a nitrogen content of 2.33% by weight, and a Tg = 133°C. Example 5 The reaction is carried out according to the procedure of Example 1, with benzamide being replaced with 7.3 g of acetamide, and the reaction being carried out at 222°C. The product polymer has an intrinsic viscosity of 0.34 dl/g a nitrogen content of 0.84% by weight, and a Tg = 124°C. Example 6 The reaction is carried out according to the procedure of Example 5, but 1 ml of 4-benzyl-pyridine is added simultaneously with benzamide and the copolymer, and the reaction is carried out at 228°C. The product polymer has an intrinsic viscosity of 0.28 dl/g, a nitrogen content of 2.39% by weight, and a Tg = 149°C. Example 7 The reaction is carried out according to the procedure of Example 1, with benzamide being replaced with 16.2 g of acetamide, and the reaction being carried out at 273°C. The product polymer has an intrinsic viscosity of 0.31 dl/g, a nitrogen content of 0.52% by weight, and a Tg = 131°C. Example 8 The reaction is carried out according to the precedure of Example 1, with an acrylic resin being used, which comprises 90% by weight of methyl-methacrylate and 10% of weight of ethyl acrylate, having an intrinsic viscosity in chloroform at 23°C of 0.45 dl/g. The product polymer has a nitrogen content of 3% by weight, and a Tg = 148°C. Example 9 The reaction is carried out according to the procedure of Example 1, with an acrylic resin being used, which is comprised of 65% by weight of methyl-methacrylate and 35% by weight of styrene, with an intrinsic viscosity in chloroform at 23°C of 0.7 dl/g. The product polymer has a nitrogen content of 2% by weight, and a Tg = 139°C. Example 10 The reaction is carried out according to the procedure of Example 1, with benzamide being replaced with 15 g of N-phenyl formamide. The product polymer has a Tg = 170°C. Example 11 The reaction is carried out according to the procedure of Example 1, with the following differences: benzamide is replaced with 13 g of chloropropionamide and the methyl methacrylate/methyl acrylate copolymer has an intrinsic viscosity of 0.9 dl/g. The product polymer has a Tg = 175°C.

Claims: Process for the preparation of imidized acrylic polymers, comprising the reaction of an acrylic resin with at least one modifying agent having general formula (I): R-X-NH-R' (I) wherein: R and R' the same or different from each other, represent hydrogen or an alkyl, cycloalkyl, aryl or alkylaryl radical containing from 1 to 20 carbon atoms, and X is a bifunctional radical selected from -CO-, -CONH-, -NHCO-, -OCO-, -SO₂- and -C₆H₄SO₂-; R optionally containing heteroatoms in case R is different from R'. Process according to claim 1, wherein the modifying agent is selected from benzamide, anisamide, acetamide, acetanilide, butyramide, benzanilide, propionamide, formamide, N-methyl-acetamide, N-methyl-benzamide, N-methyl-formamide, N-phenyl-formamide, benzenesulphamide, ethyl carbamate, benzhydrazide, chloropropionamide and N-N'-dimethylurea. Process according to claim 1, wherein imidized acrylic polymers having an optimum thermal stability, an intrinsic viscosity in tetrahydrofuran (THF) at 30°C of from 0.01 to 7 dl/g; a nitrogen content of from 0.1 to 9% by weight, and a content of imidic units of at least 5% relative to the theoretical maximum value are produced. Process according to claim 2, wherein imidized acrylic polymers having an optimum thermal stability, an intrinsic viscosity in tetrahydrofuran (THF) at 30°C of from 0.2 to 2 dl/g; a nitrogen content of from 0.5 to 7% by weight, and a content of imidic units of at least 5% relative to the theoretical maximum value are produced. Process according to any one of claims 1 to 4, wherein cyclic imidic units are produced. Process according to claim 1 which is carried out under ambient or lower pressure and at a temperature higher than the melting temperature of the acrylic resin. Process according to claim 6, wherein the reaction is carried out under a pressure of from 0.1 MPa to 1.3 x 10⁻³ kPa (760 to 10⁻² Torr) and at a temperature of from 200 to 350°C. Process according to claim 6 or 7 wherein the modifying agent is used in an amount of from 5 to 60%, relative to the acrylic monomer unit. Process according to any one of claims 6 to 8 wherein the reaction between the acrylic resin and the modifying agent is carried out in the presence of basic catalysts, acidic catalysts and/or transesterification catalysts. Process according to claim 9, wherein the catalysts comprise tertiary amines, such as dicyclohexyl-amine, 1,1,3,3-tetramethyl-guanidine, 1,3-diphenyl-guanidine, quinoline, isoquinoline, 4-benzylpyridine, 4-phenyl-pyridine, 2,3-benzodiazine, 1,4-benzodiazine, 1-benzazine, 1,3-benzodiazine, N,N'-dicyclohexyl-carbodiimide, 2,2'-bipyridyl, 2,3'-bipyridyl, 2,4'-bipyridyl or catalysts selected from HCl, Sb₂O₃, Ti(OC₄H₉)₄, NaNH₂, SnO₂, potassium or sodium alkoxides and manganese acetate. Process according to any one of claims 6 to 10 wherein the acrylic resin is used either in the molten state or dissolved in a solvent. Process according to any one of claims 6 to 11 wherein the reaction between the acrylic resin and the modifying agent is carried out in an extruder, in a mixer, or in similar devices provided with means for degassing.

Inventors: ALBIZZATI, ENRICO, CANOVA, LUCIANO, GIANNINI, UMBERTO
Applicants: ATOCHEM INDUSTRIALE S.R.L.
Application year: 1988
Main classification: C08F8
IPC codes: C08F8