IE41637B1 - Multicellular materials based on polymides and ammonia - Google Patents

Abstract

A polymer is prepared by reaction of ammonia with N,N'-4,4'-diphenylmethanebismaleimide, the polymer obtained is mixed with a blowing agent and with a surface-active agent and the mixture is heated to make it foam. The multicellular materials thus formed are employed for the manufacture of laminated sheets intended for thermal or sound insulation. [FR2279783A1]

Description

The present invention relates to multicellular njaterials made from heat-resistant polymers based on jpolyimides and ammonia.

New polymers containing imide groups have been described in French Patent No. 2,220,252, these polymers being prepared by reacting ammonia with a polymaleimide. More precisely, these thermosetting polymers are prepared by [reacting ammonia with a polyimide of the formula: in which Y represents an organic radical of valency a and a is an integer from 2 to 4, and each of A and B, which may be identical or different, represents H, CH^ or Cl, the proportions of the reagents being such that there are at least two imide groups per mol of ammonia. Reference should be made to this French Specification for further details.

The complete reaction of the polyimide with ammonia leads to cured products or resins which are insoluble in the customary solvents and do not exhibit marked softening below the temperature above which they begin to undergo degradation. However, before reaching this final stage, the reaction mixture usually passes through a stage where a product, hereafter called a prepolymer, is produced; the physical and chemical properties of this product are of course different from those of the starting materials. In particular they are soluble in polar organic solvents and possess a softening point (i.e. the temperature of the material at which a rod can be inserted into the material) at a temperature below 250°C. It is to be understood that the present invention relates to any cellular product resulting from the reaction of the polymaleimide with ammonia, in the specified proportions» in particular both to the prepolymers and to the cured resins.

Multicellular materials have now been found, according to the present invention, which are prepared from a composition consisting of: (1) a polymer prepared by reacting ammonia with a polyimide of the formula: in which Y, A, B and a are as defined above, the proportions of polyimide and ammonia being such that there are at least two imide groups per molecule of ammonia, and (2) a blowing agent and a cell-control agent.

The reaction conditions leading to the polymers used in the present invention can vary within wide limits. In particular, the ammonia can be employed as the anhydrous gas or in the form of an aqueous or organic solution, especially in alcoholic or aqueous-alcoholic solution. The polyimide can be employed in the molten state, in the form of a solution in a polar solvent such as N-methylpyrrolidone, dimethylformamide, dimethylacetamide, N-methylcaprolactam and N-acetylpyrrolidone, or in the form of a suspension, for example in water or an organic medium such as an alcohol. According to a preferred procedure, ammonia is used in the form of an aqueous solution and the polyimide is employed in solution or in suspension.

This method of working makes it possible easily to obtain an intimate mixture of the reagents. It also makes it possible to measure out the amounts of reagents easily.

As indicated above, the proportions of the reagents dl@37 are such that there are at least two imide groups per mol of ammonia. The upper limit for the ratio number of imide groups number of molecules of NH^ can, as a general rule, exceed 100/1. This ratio is preferably from 2/1 to 10/1« It is to be understood that when ammonia is used in the form of a solution, the concentration of the latter is not critical: the upper concentration limit is fixed only by the solubility of ammonia in the solvent at the temperature at which the solution is prepared; as for the lower limit, this is essentially determined by practical considerations, for example handling the smallest possible amounts of product which does not participate in the reaction.

The temperature of the reaction of ammonia with the polyimide can vary greatly, the choice of the temperature of course affecting the period of time for which the reaction mixture need be kept at the chosen temperature. With the exception of the case where the polyimide is employed in the molten state and where, consequently, the reaction mixture must be kept at a temperature at least equal to the melting point of the polyimide, the reaction can generally be carried out at a temperature below 200°C, preferably from -30° to 150°c, depending on the nature and the physical state of the reagents employed. After a period of time which generally varies from a few, say 3, minutes to 2 hours, a prepolymer is obtained, the softening point of which can vary from 50 to 250°C.

The composition based on the prepolymer described above can be converted (with the blowing agent and cell-control agent) to a multicellular material by heating at a temperature of, for example, 90°C to 250°c, more generally from 150° to 23O°C,. The duration of this heating process usually varies from at least 5 minutes and generally from 10 minutes to 5 hours. When the polymer is solid, it is advantageous t.o reduce it to a powder form and then to cold-mix (i.e. mix at ambient temperature) it intimately with the blowing agent and the cell-forming agent before subjecting it to the heat treatment indicated above.

Blowing agents which are particularly suitable advantageously have a decomposition temperature which is at least 20°C. higher than the softening point of the polymer. Blowing agents such as azodicarbonamide or the products mentioned in PLASTICS FOAMS Calvin. J. BENNlNG volume 2, page 294 to 320, 1969, Wiley-Interscience, to which reference should be made for further details, may be mentioned as examples of such adjuvants. The proportion of blowing agent, which can vary depending on the density desired for the multicellular material, is suitably from 0.1 to 10% by weight based on the weight of the polymer.

Adjuvants which make it possible to improve the homogeneity of the cellular structure of the polymers, i.e. cell-control agents, such as, for example, non-ionic surfaceactive agents like organopolysiloxanes possessing organic blocks of tho polyoxyalkylene type, are incorporated into the polymer. Such copolymers are described in, for example, PLASTIC FOAMS, Calvin. J. BENNlNG, Volume 2, pages 320-325, 1969. Cationic surface-active agents, such as N-alkyltrimethylenediamine dioleate or condensates of ethylene oxide with aminated coconut oil, are also suitable. Anionic surfaceactive agents can also be used. The proportion of cellcontrol agent depends on the nature and amount of blowing - 5 41637 agent used. It is usually not more than 5% by weight of the weight of the polymer.

Liquid or solid adjuvants in the form of a powder, spheres, platelets, granules, fibres or flakes, can also be combined with the polymer for the purpose of improving or modifying one or more characteristics of the finished article. More precisely, the adjuvants can consist of glass, carbon or asbestos fibres, synthetic polymers and, especially, polyamide-imides or aromatic polyamides, or pulverulent particles such as pyrogenic silicas, ground crude silicas, quartz, alumina, titanium oxide, talc, kaolin, mica, calcium carbonate, graphite, carbon black and barium sulphate.

Such adjuvants usually represent 5 to 50% of the woight of the polymer.

Adjuvants which make it possible to increase the hardness, the mechanical properties or the heat-resistance of the multicellular materials can also be mixed with the polymer, in particular boron oxide; this compound, which is generally used in an amount from 1 to 30% by weight of the weight of the polymer, increases the heat-resistance and the fire-resistance.

It is also possible to modify the properties of the multicellular material by incorporating resins or elastomers 3uch as phenolic resins, epoxy resins, unsaturated polyesters, polyamide-imides, polyurethanes, polysulphones or allyl polymers. It is possible to use epoxy resins such as those described in French Patent No, 2,045,087, polysulphones such as those described in French Patent No. 2,101,796, polyesters such as those described in French Patent No, 2,102,878, allyl polymers such as those described in French Patent No. 2,094,607 or polyamide-imides such as those described in French Patent No. 1,473,600.

It is possible to incorporate such resins or elastomers in amounts which can be as much as, for example, 100% relative to the weight of polymer.

The multicellular materials of this invention can be processed by various techniques such as controlled expansion in a heated mould, the preparation of blocks or semi-finished products, and the manufacture of panels in accordance with the technique described in French Patent No. 2,085,391.

It is possible to produce sandwich panels, by gluing to one or both faces, for example by means of a solution of polyamide-imide, a film which can advantageously be based on polytrimellamide-imide, or a metal strip, the thickness of which is suitably from 10 to 200 microns. Honeycomb structures or sheets of asbestos-cement and similar materials can also be glued on, making it possible to produce laminates.

The multicellular material can subsequently be stoved, for example, for a period of 2 hours and 24 hours at a temperature of 180° to 300°C.

Its mechanical properties and in particular its compressive strength can be increased in this way.

The multicellular materials according to the invention usually have an apparent specific gravity of from 0.03 to 0.8 and a uniform cellular structure, 80 to 96% of the cells being closed. They are extremely inert towards solvents and chemical agents, possess excellent resistance to heat stresses and excellent fire-resistance, and are self-extinguishing. The mechanical properties are satisfactory up to a specific gravity of the order of 0.1. In order to obtain a material which possesses essentially closed cells, it is necessary that the monomers or the prepolymers should not contain solvents which are volatile under the temperature conditions used for the expansion process.

Because of these properties, the multicellular materials of this invention are of value in numerous fields of industry. They can be used, in particular, for the production of plates, which may or may not be laminated, to provide heat or sound insulation for high temperature chambers, especially in the building industry and the aerospace industry. The following Examples further illustrate the present invention. In these Examples, the compressive strengths at 10% deformation are determined according to Standard Specifications ISO/TC 45 and 61 or ASTM D 695 and the inflammability is determined according to ASTM Standard Specification D 1692 59T.

EXAMPLE 1 900 g. (2.51 moles; 5.02 moles imide groups) of N,N'-4,4,-diphenylmethane-bis-maleimide are dispersed at ambient temperature (21°c.) in 1,098 g. of dimethylformamide (DMF). 105 g.. of an aqueous solution of ammonia containing 18.2% by weight of NH3 (1.12 mole) are introduced into the dispersion, over the course of 8 minutes, by means of a dropping funnel. The molar ratio of imide groups to NH3 is thus 4.48. During the running-in process, the temperature rises to 42°C. The mixture is heated to 60°C., and a clear solution is obtained in 10 minutes. The solution is cooled to 24°c.ι over 40 minutes and then, whilst stirring vigorously, the polymer is precipitated in 6 litres of deionised water.

The polymer is filtered off, washed with water and dried in an oven at 50°C., to constant weight and then in vacuo - 8 41637 (1 mm. of mercury) at 80°C. for 7 hours. 013 g. of a polymer with a softening point of 14O°C. .mil .ι i ul io: K _ number of double bonds of the bis-malcimide number of NH^ groups equal to 2.5, are collected.

After grinding, a powder of particle size less than 50 microns is obtained. 100 g. of the polymer obtained are mixed with 4 g. of 4,4'-diphenoxy-disulphonylhydrazide and 1 g. of a 50% by weight solution of N-alkyltrimethylenediamine dioleate in methanol.

After homogenisation, this mixture is placed in a metal mould. It is heated at 1SO°C., for 1 hour in a ventilated oven. A block of yellow multicellular material of specific gravity 0.072 is obtained. It is stoved at 200°C., for 24 hours. The colour changes from yellow to light brown but no loss in weight is observed.

The material obtained is non-inflammable according to ASTM Standard Specification D 1692 59T.

Its compressive strength at ambient temperature is 4.31 kg/cm in the direction of expansion of the material.

When measured at 200°C., the compressive strength is 3.98 kg/cm2.

EXAMPLE 2 The procedure indicated in Example 1 is followed, but the mixture contains 100 g. of the polymer, 3 g. of 4,4'-diphenoxy-disulphonylhydrazide and 1 g. of a 50% by weight solution of N-alkyltrimethylenediamine dioleate in methanol.

A multicellular material with a specific gravity of 0.089 is obtained. o The compressive strengths after stoving are 6.08 kg/cm measured at ambient temperature and 5.02 kg/cm measured at 200°C.

EXAMPLE 3 The procedure indicated in Example 1 is followed, but the mixture contains 90 g. of the polymer, 10 g. of a polyester prepared by reacting maleic acid, propylene glycol and allyl phthalate, 4 g. of 4,4'-diphenoxydisulphonylhydrazide and 1 g. of a 50% by weight solution of N-alkyltrimethylenediamine dioleate in methanol.

A multicellular mass with a specific gravity of 0.09 is obtained. The product is non-inflammable according to ASTM Standard Specification D 1692 59T.

Claims (15)

1. (1) a polymer prepared by reacting ammonia with a

1. Process for preparing a multicellular materia], which comprises heating a composition comprising:

2. Process according to claim 1, in which the 15 blowing agent has a decomposition temperature which is at least 20°C. higher than the softening point of the polymer employed.

3. Process according to claim 1 or 2 in which the composition contains 0.1 to 10% by weight of blowing 20 agent based on the weight of the polymer.

4. Process according to any one of claims 1 to 3, in which the cell-control agent is a cationic, non-ionic or anionic surface-active agent. 5. On one or both faces with a film.

5. Process according to any one of the preceding claims in which the composition contains the cell-control agent in an amount up to 5% by weight based on the weight of the polymer. 5 5 polyimido of the formula: in which V represents an organic radical of valency a, a is an integer from 2 to 4, and each of A and B, which may bo identical or differentι represents H, CH^ or Cl,

6. Process according to any one of the preceding claimsι in which the composition also contains at least one phenolic resin, epoxy resin, unsaturated polyester, polyamideimide, polysulphone or polyurethane.

7. Process according to any one of the preceding

8. Process according to claim 7 in which the filler is glass, carbon or asbestos fibres.

9. Process according to any one of the preceding

10. Process according to claim 1 substantially as hereinbefore described. 25 10 claims, in which the composition also contains at least one pulverulent or fibrous inorganic or organic filler. 10 the proportions of polyimide and ammonia being such that there are at least two imide groups per molecule of ammonia, and (2) a blowing agent and a cell-control agent.

11. Process according to claim 1 substantially as described in any one of Examples 1 to 3. 416 3 7

12. A multicellular material whenever prepared by a process as claimed in any one of the preceding claims. 12 claims which comprises; a) preparing the polymer by reacting the polyimide with ammonia at a temperature of -30° to 200°C., for 3 minutes to two hours, b) cold-mixing the polymer obtained, in powder form, with 20 the blowing agent and the cell-control agent, and c) heating the mixture at 90°C. to 25O°C. for at least 5 minutes.

13. A composite material which comprises a layer of a multicellular material as claimed in claim 12 covered

14. A composite material which comprises a layer of multicellular material as claimed in claim 12 covered on one or both faces with a polyamide-imide film, a metal film, a honeycomb structure or an asbestos-cement sheet. 0

15. A compisite material according to claim 13 substantially as hereinbefore described.