SMALL-CELL POLYSTYRENE FOAMS, AND PROCESS FOR PRODUCING SAME

Abstract

The invention relates to a process for producing small-cell foams from a styrene-polymer component (S) and an additive of formula (I), wherein Z represents a C.sub.1-C.sub.5-alkylene group or an oxygen or sulfur atom, R.sub.1 and R.sub.2 represent, e.g., a C.sub.3-C.sub.12-alkyl residue, C.sub.3-C.sub.12-cycloalkyl residue or benzyl residue; and R.sub.3, R.sub.4, R.sub.5 and R.sub.6 represent hydrogen or a C.sub.1-C.sub.6-alkyl residue, comprising the steps of: —heating at least a styrene-polymer component (S) to obtain a molten, polymeric molding compound, —introducing a propellant (T) into the molten molding compound to form a foamable composition (Z), and—foaming the foamable composition to obtain a foamed molding, the molten polymeric molding compound containing at least one carboxylic acid derivative of the general formula (I).

##STR00001##

Claims

1-17. (canceled)

18. A process for producing a foam from at least one styrene polymer component (S) and at least one additive of the general formula (I), comprising the steps of: a. heating at least one styrene polymer component (S) to give a melted polymeric molding compound, b. introducing a blowing agent (T) into the melted polymeric molding compound, to form a foamable composition (Z), and c. foaming the foamable composition (Z) to give a foamed molding, wherein at least one carboxylic bisamide of the general formula (I) is used in the melted polymeric molding compound, ##STR00012## wherein: Z is a C.sub.1-C.sub.5 alkylene group or an oxygen atom or a sulfur atom; R1 and R2 independently of one another are a branched C.sub.3-C.sub.12 alkyl radical or unbranched C.sub.1-C.sub.12 alkyl radical, a C.sub.3-C.sub.12 cycloalkyl radical, or a benzyl radical; and R3, R4, R5, and R6 each independently of one another are hydrogen, an unbranched C.sub.1-C.sub.6 alkyl radical, or a branched C.sub.3-C.sub.6 alkyl radical.

19. The process of claim 18, wherein in the general formula (I) R1 and R2 independently of one another are a C.sub.3-C.sub.12 cycloalkyl radical.

20. The process of claim 19, wherein in the general formula (I) R1 and R2 independently of one another are a cyclohexyl radical, a cyclopentyl radical, a butyl radical, or a benzyl radical.

21. The process of claim 18, wherein in the general formula (I) Z is a methylene group and R3, R4, R5, and R6 each independently of one another are a C.sub.1-C.sub.6 alkyl radical.

22. The process of claim 18, wherein the carboxylic bisamide of the general formula (I) is used in an amount of 0.01 to 2.0 wt %, based on the total weight of the melted polymeric molding compound.

23. The process of claim 18, wherein the blowing agent (T) selected from the group consisting of pentane, cyclopentane, carbon dioxide, ethanol, and a mixture thereof is introduced into the melted polymeric molding compound.

24. The process of claim 18, wherein the styrene polymer component (S) used is a polystyrene (PS) and/or a copolymer containing styrene and acrylonitrile.

25. The process of claim 24, wherein the styrene polymer component (S) used is styrene-acrylonitrile (SAN).

26. A foam obtainable by a process of claim 18.

27. The foam of claim 26, having a density in the region of at least 30 kg/m.sup.3 and having an at least 50% closed-cell structure.

28. The foam of claim 26, having a density in the range of 45-85 kg/m.sup.3 and having an at least 90% closed-cell structure.

29. The foam of claim 26, having a mean cell diameter (D) of 0.1-25.0 micrometers.

30. The foam of claim 26, having a mean cell diameter (D) of 1.0-16.0 micrometers.

31. The foam of claim 26, which is a polystyrene-based foam.

32. The foam of claim 26, which is a styrene-acrylonitrile copolymer-based foam.

33. A polymer composition for producing a foam, comprising at least one styrene polymer component (S) and at least one carboxylic bisamide of the general formula (I), ##STR00013## wherein: Z is a C.sub.1-C.sub.5 alkylene group or an oxygen atom or a sulfur atom; R1 and R2 independently of one another are a branched C.sub.3-C.sub.12 alkyl radical or unbranched C.sub.1-C.sub.12 alkyl radical, a C.sub.3-C.sub.12 cycloalkyl radical, or a benzyl radical; and R3, R4, R5, and R6 each independently of one another are hydrogen, an unbranched C.sub.1-C.sub.6 alkyl radical, or a branched C.sub.3-C.sub.6 alkyl radical.

34. The polymer composition of claim 33, comprising further additives.

35. A method to reduce the mean cell diameter (D) of a foam in the production of foams from at least one polymeric material, comprising introducing a carboxylic bisamide of the general formula (I) of claim 18 ##STR00014## as an additive.

36. A process for preparing a carboxamide of the general formula (I) of claim 18 by reacting at least one activated carboxylic acid derivative with a bis-amine.

37. A carboxylic bisamide of the general formula (I) ##STR00015## wherein: Z is a —CH.sub.2 group; R1 and R2 independently are benzyl, cyclohexyl, n-butyl, or tert-butyl; and R3, R4, R5, and R6 each independently are methyl or ethyl.

Description

[0096] FIG. 1 shows two scanning electron micrographs (A at 50 times magnification and B at 250 times magnification) of cells of a (pure) polystyrene foam (“neat PS”) produced without addition of a bisamide of the formula (I). The foam is based on commercial polystyrene PS 168N (INEOS STYROLUTION, Frankfurt). It is clearly apparent that the cells of the foam have a large mean cell size. The cell size distribution of the PS foam is also nonuniform.

[0097] FIG. 2 shows two scanning electron micrographs (A at 50 times magnification and B at 250 times magnification) of cells of a polystyrene foam produced using the bisamide of the formula (I). The foam is based on polystyrene PS168N (INEOS STYROLUTION). In this case the additive used as component (3b) was the compound N,N′-[methylenebis(2,6-diethyl-4,1-phenylene)]biscyclo-hexanecarboxamide] in an amount of 0.1 percent by weight.

[0098] It is clearly apparent that the morphology of the cells of the foam is closed-cell and small-cell. A small mean cell size (14.4+/−4.7 micrometers) and a narrow cell size distribution are evident.

[0099] The polystyrene foam here has a cell density of 4.3×10.sup.8 cm.sup.−3 and also a foam density of 76.5 kg/m.sup.3. There is also no pronounced bimodal cell size distribution in the foam, as often occurs in the case of other additives, such as trisamide derivatives, for example.

[0100] The invention is further elucidated in more detail by the following examples and claims.

EXAMPLES

[0101] The “angled” carboxylic bisamide derivatives used may be synthesized according to the processes described below; all chemicals for the preparation are available commercially and can be used without further purification.

[0102] The medium-viscosity silicone oil M100 (Carl Roth GmbH+Co. KG) was used as the oil bath for the foaming of the samples in the batch foam process. The blowing agent CO.sub.2 with 99.995% purity was purchased from Rießner Gase GmbH.

[0103] Characterization took place using the following analytical methods and techniques:

[0104] Differential scanning calorimetry (DSC): DSC analyses were carried out using a Mettler Toledo DSC 2. Around 6-12 mg of a compound were weighed out in a 30 μL high-pressure crucible to this end. The angled bisamide derivatives 1a-d, 2a, 2d, 3a and 3d were measured in a temperature range of 25-300° C. and the angled bisamide derivatives 2b-c and 3b-c in a temperature range of 25-350° C., in each case with a rate of 10 K/min. Each heating and cooling step was repeated three times. The recorded melting points were taken from the second heating step.

[0105] Mass spectrometry (MS): MS analyses were carried out using electron spray ionization on a customary instrument (FINNIGAN MAT 8500 spectrometer from Thermo-Fisher Scientific).

[0106] Scanning electron microscopy (SEM): Scanning electron micrographs were recorded on a customary microscope (Zeiss LEO 1530) with an acceleration voltage of 3 kV and using an internal lens detector or SE2 detector.

[0107] For this analysis, the foam samples were first cryofractured with liquid nitrogen and the fracture edges were sputter-coated with 2 nm of platinum under an argon atmosphere using a coater (Cressington Sputter Coater 208HR). Prior to sputtering, the samples were additionally lined on the sides with self-adhesive copper foil, in order to ensure better conductivity.

[0108] Thermal conductivity: The thermal conductivity of the foam samples was measured with a customary heat flow meter (LaserComp FOX 50 from TA Instruments). The foam samples were cut into cylinders 60 mm in diameter with a thickness (L) of between 3 mm and 8 mm, depending on the extruded thickness of the foam. The samples were positioned between two temperature-conditioned plates.

[0109] The temperature of the upper plate was adjusted to 30° C. and that of the lower plate to 20° C., producing a temperature difference (ΔT) of 10° C. along the sample thickness. The resulting heat flow (Q/A) through the foam sample was measured by means of two thin-film heat flow transducers. The thermal conductivities (t) were calculated according to formula (1):

[00001]$\begin{array}{cc}{\lambda }_t=\frac{Q.Math.L}{A.Math.\Delta T}& \left(1\right)\end{array}$

[0110] At least five samples of each foam were measured at different positions and average values for the thermal conductivity were determined.

[0111] Foam density: The foam density was determined by the water displacement method according to standard ISO 1183, using an analytical balance (Mettler Toledo XP 205) with density kit. For this analysis, small blocks were cut from the samples and weighed in air (m.sub.air). After that, the buoyancy of the samples underwater was determined. (m.sub.water; ρ.sub.water: density of the water at measurement temperature). The resulting density (ρ.sub.foam) was calculated using the following equation:

[00002]${\rho }_{\mathrm{foam}}=\frac{m_{\mathrm{air}}}{m_{\mathrm{air}}-m_{\mathrm{water}}}.Math.{\rho }_{\mathrm{water}}$

[0112] Each measurement was carried out with three different blocks of the sample in question, and the average value was recorded.

[0113] Morphology: The morphology of the foam samples was analyzed by means of SEM micrograph. A region (A.sub.cell) of at least 70 cells of each sample was considered. On the assumption of a circular shape to the cells, the following equation was employed for determining the size (Φ) of all the individual cells:

[00003]$\Phi =2.Math.\sqrt{\frac{A_{\mathrm{cell}}}{\pi }}$

[0114] The arithmetic mean ((D) of all the calculated cells, with standard deviation, is listed for each foam.

Example 1 Preparation of the Carboxylic Bisamide Derivatives of the Formula (I)

[0115] Starting from the corresponding aromatic bisamine compounds and acid derivatives, the aromatic bisamide derivatives below were prepared, and are readily soluble in the polymer (PS, SAN) at processing temperature.

[0116] Compounds 1a-d, 2a-d, 3a-d were purified and characterized. The syntheses of these bisamide additives of the formula (I) are described below.

1a Synthesis of N,N′-[methylenebis(4,1-phenylene)]bis-[benzamide]

[0117] 5 g (25.2 mmol) of 4,4′-diaminodiphenylmethane, 4.5 mL of pyridine and 100 mL of NMP were mixed in a Schlenk flask and cooled to around 0-5° C. Under an argon atmosphere, 7.79 g (55.4 mmol) of benzoyl chloride were added dropwise and the mixture was subsequently warmed to room temperature. After an hour, the reaction mixture was precipitated from ice-water and the solid obtained was isolated by filtration and dried. For further purification, the solid was heated at reflux in 500 mL of MeOH, filtered and dried under a high vacuum. 9.65 g (95%) of the product 1a were obtained in the form of a white powder. Characterization: MS: (70 eV), m/z (%): 406 [M.sup.+]; DSC: T.sub.m=249° C.

1b Synthesis of N,N′-[methylenebis(4,1-phenylene)]bis-[cyclohexanecarboxamide]

[0118] 3 g (15.0 mmol) of 4,4′-diaminodiphenylmethane, 20 mL of pyridine, 100 mL of NMP and LiCl were mixed in a Schlenk flask and cooled to around 0-5° C. Under an argon atmosphere, 4.9 g (33 mmol) of cyclohexanecarbonyl chloride were added dropwise. The reaction mixture was subsequently heated at 80° C. for 12 h and then precipitated from ice-water. The solid obtained was isolated by filtration and dried. For further purification, the solid was recrystallized in 500 mL of MeOH, filtered and dried under a high vacuum. 5.5 g (88%) of the product 1b were obtained in the form of a white powder. Characterization: (88%); MS: (70 eV), m/z (%): 418 [M.sup.+]; DSC: T.sub.m=221° C.

1c Synthesis of N,N′-[methylenebis(4,1-phenylene)]bis-[2,2-dimethylpropanamide]

[0119] 3 g (15 mmol) of 4,4′-diaminodiphenylmethane, 20 mL of pyridine, 100 mL of NMP and LiCl were mixed in a Schlenk flask and cooled to around 0-5° C. Under an argon atmosphere, 4 g (33 mmol) of pivaloyl chloride were added dropwise. The reaction was stirred at 80° C. for 12 h, followed by precipitation from ice-water. The resulting solid was isolated by filtration and dried. For further purification, the solid was recrystallized in 500 mL of ethyl acetate, isolated by filtration and dried under a high vacuum. 4.1 g (75%) of the product 1c were obtained in the form of a white powder. Characterization: MS: (70 eV), m/z (%): 366 [M.sup.+]; DSC: T.sub.m=239° C.

1d Synthesis of N,N′-[methylenebis(4,1-phenylene)]bis-[pentanamide]

[0120] 5 g (25.21 mmol) of 4,4′-diaminodiphenylmethane, 4.5 mL of pyridine and 100 mL of NMP were mixed in a Schlenk flask and cooled to around 0-5° C. Under an argon atmosphere, 6.02 g (55.47 mmol) of valeroyl chloride were added dropwise and the mixture was warmed to room temperature. After a reaction time of one hour, the mixture was precipitated from ice-water. The resulting solid was then isolated by filtration and dried. For further purification, the solid was recrystallized in 300 mL of MeOH, filtered and dried under a high vacuum. 8.8 g (95%) of the product 1d were obtained in the form of a white powder. Characterization: MS: (70 eV), m/z (%): 366 [M.sup.+]; DSC: T.sub.m=192° C.

2a Synthesis of N,N′-[methylenebis(2,6-dimethyl-4,1-phenylene)]bis[benzamide]

[0121] 5 g (19.65 mmol) of 4,4′-methylenebis(2,6-dimethyl-aniline), 3.5 mL of pyridine and 100 mL of NMP were mixed in a Schlenk flask and cooled to around 0-5° C. Under an argon atmosphere, 6.07 g (43.23 mmol) of benzoyl chloride were added dropwise and the mixture was warmed to room temperature. After an hour, the reaction mixture was precipitated from ice-water. The resulting solid was then isolated by filtration and dried. For further purification, the solid was heated under reflux in 500 mL of MeOH, filtered and dried under a high vacuum. 7.5 g (82%) of the product 2a were obtained in the form of a white powder. Characterization: MS: (70 eV), m/z (%): 462 [M.sup.+]; DSC: T.sub.m=225° C.

2b Synthesis of N,N′-[methylenebis(2,6-dimethyl-4,1-phenylene)]bis[cyclohexanecarboxamide]

[0122] 3.56 g (14.00 mmol) of 4,4′-methylenebis(2,6-dimethyl-aniline), 4.28 mL of Et.sub.3N and 100 mL of THF were mixed in a Schlenk flask and cooled to around 0-5° C. Under an argon atmosphere, 4.51 g (30.76 mmol) of cyclohexane-carbonyl chloride were added dropwise. After 48 h at 60° C., the reaction mixture was precipitated from ice-water. The resulting solid was then isolated by filtration, washed with water and subsequently dried. For further purification the solid was recrystallized in 250 mL of DMF, filtered and dried under a high vacuum. 5.6 g (84%) of the product 2b (formula (II)) were obtained in the form of a white powder. Characterization: MS: (70 eV), m/z (%): 474 [M.sup.+]; DSC: T.sub.m=307° C.

##STR00007##

2c Synthesis of N,N′-[methylenebis(2,6-dimethyl-4,1-phenylene)]bis[2,2-dimethylpropanamide]

[0123] 4 g (15.72 mmol) of 4,4′-methylenebis(2,6-dimethyl-aniline), 2.8 mL of pyridine and 100 mL of THF were mixed in a Schlenk flask and cooled to around 0-5° C. Under an argon atmosphere, 4.17 g (34.59 mmol) of pivaloyl chloride were added dropwise and the mixture was warmed to room temperature. After an hour the reaction mixture was precipitated from ice-water. The solid was then isolated by filtration and dried. For further purification the solid was first recrystallized in 100 mL of MeOH, followed by filtration over silica gel with DMF as eluent. The solvent was removed by concentration and the solid was precipitated from water and dried at 80° C. 4.9 g (74%) of the product 2c were obtained in the form of a white powder. Characterization: MS: (70 eV), m/z (%): 422 [M.sup.+]; DSC: T.sub.m=310° C.

2d Synthesis of N,N′-[methylenebis(2,6-dimethyl-4,1-phenylene)]bis[pentanamide]

[0124] 3 g (11.79 mmol) of 4,4′-methylenebis(2,6-dimethyl-aniline), 2.4 mL of pyridine and 200 mL of THF were mixed in a Schlenk flask and cooled to around 0-5° C. Under an argon atmosphere, 2.81 g (25.94 mmol) of valeroyl chloride were added dropwise and the mixture was warmed to room temperature. After an hour, the reaction mixture was precipitated from ice-water. The solid was then isolated by filtration and dried. For purification, the solid was recrystallized in 300 mL of MeOH, filtered and dried under a high vacuum. 3.6 g (72%) of the product 2d were obtained in the form of a white powder. Characterization: MS: (70 eV), m/z (%): 422 [M.sup.+]; DSC: T.sub.m1=190° C., T.sub.m2=258° C.

3a Synthesis of N,N′-[methylenebis(2,6-diethyl-4,1-phenylene)]bis[benzamide]

[0125] 5 g (16.10 mmol) of 4,4′-methylenebis(2,6-diethyl-aniline), 2.8 mL of pyridine and 100 mL of NMP were mixed in a Schlenk flask and cooled to around 0-5° C.

[0126] Under an argon atmosphere, 4.98 g (35.42 mmol) of benzoyl chloride were added dropwise and the mixture was warmed to room temperature. After an hour, the reaction mixture was precipitated from ice-water. The resulting solid was then isolated by filtration and dried. For further purification, the solid was heated under reflux in 500 mL of MeOH, filtered and dried under a high vacuum. 7.0 g (83%) of the product 3a were obtained in the form of a white powder. Characterization: MS: (70 eV), m/z (%): 518 [M.sup.+]; DSC: T.sub.m=258° C.

3b Synthesis of N,N′-[methylenebis(2,6-diethyl-4,1-phenylene)]bis[cyclohexanecarboxamide]

[0127] 9 g (28.00 mmol) of 4,4′-methylenebis(2,6-diethyl-aniline), 5.1 mL of pyridine and 120 mL of NMP were mixed in a Schlenk flask and cooled to around 0-5° C. Under an argon atmosphere and with ice cooling, 9.34 g (63.00 mmol) of cyclohexanecarbonyl chloride were added dropwise and the mixture was warmed to room temperature. After a reaction time of two hours, 100 mL of water was added to the mixture, which was stirred for a further hour and then the solid was filtered. For further purification the solid was heated under reflux in 200 mL of acetone, filtered and dried under a high vacuum. 14.2 g (92%) of the product 3b (formula (III)) were obtained in the form of a white powder. Characterization: MS: (70 eV), m/z (%): 530 [M.sup.+]; DSC: T.sub.m=297° C.

##STR00008##

3c Synthesis of N,N′-[methylenebis(2,6-diethyl-4,1-phenylene)]bis[2,2-dimethylpropanamide]

[0128] 4.34 g (14.00 mmol) of 4,4′-methylenebis(2,6-diethyl-aniline), 4.3 mL of Et.sub.3N and 50 mL of THF were mixed in a Schlenk flask and cooled to around 0-5° C. Under an argon atmosphere, 3.71 g (30.80 mmol) of pivaloyl chloride were added dropwise and the reaction mixture was heated to 60° C. After 48 h the mixture was precipitated from ice-water. The resulting solid was then isolated by filtration and recrystallized in 500 mL of MeOH. For further purification, the solid was recrystallized in 250 mL of DMF, filtered and dried under a high vacuum. 4.8 g (71%) of the product 3c were obtained in the form of a white powder. Characterization: MS: (70 eV), m/z (%): 478 [M.sup.+]; DSC: T.sub.m=328° C.

3d Synthesis of N,N′-[methylenebis(2,6-diethyl-4,1-phenylene)]bis[pentanamide]

[0129] 4.34 g (14.00 mmol) of 4,4′-methylenebis(2,6-diethyl-aniline), 4.3 mL of Et.sub.3N and 50 mL of THF were mixed together in a Schlenk flask and cooled to around 0-5° C. Under an argon atmosphere, 3.71 g (30.8 mmol) of valeroyl chloride were added dropwise, followed by heating to 50° C. After 3 h, the reaction mixture was precipitated from ice-water. The resulting solid was then isolated by filtration and washed with H.sub.2O. For further purification, the solid was recrystallized in 200 mL of MeOH, filtered and dried under a high vacuum. 3.7 g (56%) of the product 3d (formula (IV)) were obtained in the form of a white powder. Characterization: MS: (70 eV), m/z (%): 478 [M.sup.+]; DSC: T.sub.m1=120° C., T.sub.m2=220° C.

##STR00009##

[0130] All carboxylic bisamides depicted in table 1 below are subject to the formula (I). They can be prepared readily even in substantial quantities. The stated compounds are soluble in polystyrene and SAN at processing temperature.

TABLE-US-00001 TABLE 1 Angled bisamides of the general formula (I) used Bisamide Substituents Substituents additive R.sub.3, R.sub.4, R.sub.5, R.sub.6 R.sub.1, R.sub.2 1 a H Benzyl b Cyclohexyl c tert-Butyl d n-Butyl 2 a Methyl Benzyl b Cyclohexyl c tert-Butyl d n-Butyl 3 a Ethyl Benzyl B Cyclohexyl C tert-Butyl D n-Butyl

Example 2 Comparative Carboxamide Derivatives

[0131] For the comparative experiments, firstly the trisamide additive Irgaclear® XT 386 (BASF SE) and secondly the bisamide additive NJ Star NU100 (N,N′-dicyclohexyl-2,6-naphthalenedicarboxamide) of New Japan Chemical were used.

[0132] The symmetrical aromatic trisamide Irgaclear® XT 386 used as a transparency booster for polypropylene (1,3,5-tris(2,2-dimethylpropionylamino)benzene; BASF, formula (V)) may be prepared analogously from 1,3,5-trisaminobenzene and acyl chloride.

##STR00010##

[0133] A (nonangled) aromatic bisamide derivative may be prepared from naphthalene-2,6-dicarboxylic acid and cyclohexylamine. It is also sold by New Japan Chemical as product NJ STAR NU100 (formula (VII)).

##STR00011##

Example 3 Production of the Foams

[0134] Polystyrene foams were produced by the process of the invention. This was done using a commercial polystyrene (PS168N, INEOS STYROLUTION, Frankfurt am Main) in the form of 3 mm cylindrical pellets (3×2 mm). For the polystyrene an average molecular weight Mw of 340 000 g/mol was ascertained.

[0135] a) Production of the Polymer Powder/Additive Powder Mixtures (Masterbatch)

[0136] For this purpose the polymer pellets were first ground using an ultracentrifuge (Retsch ZM200 mill) at a rotary speed of 18 000 rpm with a sieve mesh size of 1000 μm in order to ensure further incorporation and distribution of the additive. During the grinding process, the polymer was cooled with liquid nitrogen.

[0137] The ground PS was subsequently provided with 1.0 wt % of the corresponding additive for each powder-powder masterbatch, and was homogenized at 50 rpm with a Heidolph Reax 2 mixer.

[0138] b) Batch Foam Process:

[0139] Compounding of Polymer-Additive Concentration Series and Injection Molding to Form Specimens

[0140] Preparation was carried out with a co-rotating twin-screw compounder (DSM Xplore 15 ml). The components were mixed for 5 minutes with a rotary speed of 50 rpm at 260° C. The polymer melt was subsequently left in the injection molding vessel for 2 minutes. Because it is inconvenient to empty the extruder completely and since a defined dead space is left, it is advantageous to prepare a dilution series in order to enable different concentrations. At the start the extruder is filled with 13.5 g of the corresponding material. About 8.1 g can be transferred into the injection molding vessel, while 5.4 g remain in the compounder. With this knowledge it is possible to achieve the desired concentrations.

[0141] The following eight concentrations of the above additives in the polymer composition were produced: [0142] 1.0; 0.75; 0.5; 0.25; 0.1; 0.05; 0.025 and 0.01 wt %.

[0143] Injection molding was carried out using the micro-injection molding machine DSM Xplore 12 mL. The vessel had a temperature of 250° C. and the melt was injected with a pressure of 6 bar for 10 seconds. The pressure was maintained for a further 10 seconds. Round polymer plaques 27 mm in diameter and 1.1 mm in thickness were obtained and tested. In order to eliminate internal stresses in the polymer samples from the injection molding process, they are conditioned at 135° C. for 4 hours in a closed iron mold. The stress-free samples guarantee uniform foaming.

[0144] Saturation and Foaming of the Polymer Specimens in the Batch Foam Process

[0145] After conditioning, the polymer samples were placed in a BERGHOF HR-500 high-pressure autoclave and saturated with 50 bar of CO.sub.2 at room temperature for 24 hours.

[0146] After the removal of pressure, the samples were left in the air for 18 min in order to achieve a CO.sub.2 saturation of around 6.5%. The samples were subsequently immersed for 15 seconds in a hot silicone oil bath at 130° C. in order to induce foaming. In order to stabilize the cells, the resultant foams were cooled first in a cold oil bath and thereafter in a cold water bath for about 20 seconds each. Lastly the resultant foams were washed in soapy water and dried in air for 12 hours prior to further analysis.

[0147] c) Foam Extrusion

[0148] The foam extrusions were carried out on a tandem extrusion line (Dr. Collin GmbH) (twin-screw extruder with 25 mm screw and L/D 42; single-screw extruder with 45 mm screw and L/D 30), equipped with a slot die having a 0.6 mm slot and 3 mm width.

[0149] Extruded pure XPS foam and also a number of XPS foams each with three selected additive concentrations, namely 0.1 and 0.2 and 0.5 wt %, were produced and analyzed. Analogous trials are carried out with SAN foams.

[0150] The various additive concentrations in the polymer were obtained by dilution of a masterbatch with pure polymer pellets, using a gravimetric feeder, by monitoring of the flow rates.

[0151] A combination of 4 wt % of CO.sub.2 and 3 wt % of ethanol was used as (physical) blowing agent. To obtain an XPS reference, PS pellets without carboxamide additive were extruded in the same way.

[0152] The relevant process parameters for the foam extrusion are summarized in table 2.

TABLE-US-00002 TABLE 2 Process parameters for the foam extrusion of PS foams Entry Exit melting melting Die temper- temper- temper- Screw Through- Blowing agent ature ature ature speed put [wt %] [° C.] [° C.] [° C.] [rpm] [kg/h] CO.sub.2 EtOH 260 106-130 123-132 8 4.5 4 3

[0153] Table 3 sets out the results of various extruded foams produced, based on the polystyrene above. The extruded foams differ in the carboxamide additives used (0.1 wt % in each case).

TABLE-US-00003 TABLE 3 Mean cell size and foam density of extruded PS foams without additive, with 0.1 or 0.5 wt % Irgaclear XT 386, with 0.1, 0.2 or 0.5 wt % carboxamide 3b Mean cell size and Foam standard deviation density Additive (micrometers) (kg/m.sup.3) No additive  632.1 +/− 183.9 52.3 Irgaclear XT 386 25.7 +/− 7.8 72.6 (0.1 wt %) Irgaclear XT 386  31.3 +/− 10.1 — (0.5 wt %) Bisamide (3b) 14.4 +/− 4.7 76.5 (0.1 wt %) Bisamide (3b) 14.7 +/− 5.5 82.8 (0.2 wt %) Bisamide (3b) 10.7 +/− 4.3 71.2 (0.5 wt %)

[0154] The polystyrene foam with carboxamide (3b) shown in table 3 exhibits a small cell size and consequently a significant increase in the cell count even when using 0.1 wt % of the additive. Small-cell, closed-cell foams are obtained.

[0155] When 0.2 wt % of carboxylic bisamide (3b) is used in the polystyrene, the mean cell size of the foam is 14.7 and the foam density is 82.8 kg/m.sup.3. When 0.5 wt % of carboxylic bisamide (3b) is used in the polystyrene, the mean cell size of the foam is 10.7 micrometers and the foam density is 71.2 kg/m.sup.3.

[0156] With the other bisamide derivatives (1a-d), (2a-d) and (3a, c-d) of the invention as well, in the batch foam process at the tested concentrations (0.1; 0.25; 0.5 wt % of the bisamide) in polystyrene, small-cell and closed-cell foams were obtained in each case, and also have a very largely homogeneous cell size.

[0157] When the known trisamide derivative Irgaclear XT 386 was used in the batch foam process, conversely, at the tested concentrations (0.1; 0.25; 0.5 wt % of the trisamide) in polystyrene, the foams obtained in each case had much larger cells, which also did not have a homogeneous cell size.

[0158] In the foam extrusion process, using 0.1 wt % of Irgaclear XT 386 in the polystyrene, the mean cell size of the foam was 25.7+/−7.8 micrometers, and when using 0.5 wt % in the polystyrene the mean cell size of the foam was 31.3 micrometers.

[0159] Extensive analyses of the thermal conductivity of the XPS foams were also carried out (on round plaques 60 mm in diameter). It was found that the bisamides of the formula (I), even used at a low concentration in the polymer, lead to much better insulation properties (e.g., at 0.1 wt % of the bisamide 3b in the above polystyrene of +7%) in the foams than in the case of corresponding foams produced with the trisamide additive Irgaclear XT 386 in polystyrene.

[0160] In further analyses with the batch foam process it emerged that the additives of the invention can also be used advantageously in other polymers. Hence with the bisamide derivative (such as 3b, for example) it was possible, even using 0.1 wt %, to achieve a significant reduction in the mean cell size in a styrene-acrylonitrile copolymer (Luran® 25100, INEOS Styrolution).

[0161] The polymer foam obtained with carbon dioxide (130° C., 25 seconds) had a mean cell diameter of the foam of 16.4+/−6.1 micrometers and the foam density was 39.9 kg/m.sup.3. A significant increase in the cell count was found, and a small-cell, closed-cell SAN foam was obtained. The cell size distribution was homogeneous as well.

[0162] The compounds of the formula (I) therefore enable the provision of new closed-cell foam products which can be employed advantageous even in composite elements (having two or more layers).