GB2238314A - Polycyanoamides and polyamidoiminoimides - Google Patents

Abstract

Polyamidoiminoimides and their precursors are disclosed. Whilst aliphatic polymers are included in the invention, preferred polymers are aromatic, preferably based on benzene or polyaromatic monocyanodicarboxylic acids, the latter either being directly linked together or being linked by -CO-, SO2 etc or being fused ring systems, and aromatic diamines. The polyamidoiminoimides are prepared by the in situ cyclisation of the corresponding polycyanoamides.

Description

Polymers This invention relates to polymers and to process for their preparation.

Over recent years, high performance plastic materials have found application in a diversity of industries such as the aerospace, electronics and automotive industries. Such materials exhibit an attractive combinstion of properties including strength, stiffness, toughness and temperature resistance. These types of materials are usually linear, high molecular weight thermoplastics. In many instances, these materials are replacing thermoset materials which, owing to their highly cross-linked structure, frequently exhibit brittleness.

Polyimides are particularly attractive materials in that they exhibit many of the properties of thermoplastic materials whilst also exhibiting a tendency to intramolecular cross-linking via cyclisation reactions. Such cyclisation reactions, in the most desirable polymers, render the polymers effectively thermoset, ie the polymers exhibit a very high or have no discernible glass transition temperature, Tg.

Additionally, polyimides exhibit outstanding thermooxidative resistance.

The penalty for these attractive properties in polyimides is the production of volatile substances, usually water, during the cyclisation reactions which can interfere with the consolidation of structures made from the polymer and which can have a deleterious affect on the molecular weight of the polymer.

A cyclisation reaction in which no volatiles are produced is known (A N Pravednikov, E N Teleshov and I V Vasilieva, IUPAC Macromolecules Conf, Helsinki, (1972), 2, 843). The cyclisation involves the reaction of for example 2,5-dicyanoterephthalic diacid dichloride with an aromatic diamine to give a polyiminoimide product. However, such polymers do not appear to have been developed, possibly owing to difficulties in preparing the dicyanodiacid dichloride monomer (see K A Hodd and P Shadbolt, Brit Polym J, (1983), 15, 201).

It is an object of the present invention to provide novel polyimides and processes for their preparation which avoids the aforementioned disadvantage.

According to the present invention, a polymer comprises a repeat unit of formula I and/or formula II:

wherein Ar is a trivalent organic radical derived from an active derivative of a monocyanodicarboxylic acid in which the cyano group is located relative to one of the acid derivative groups such that imidisation can occur therebetween; and R is a divalent organic radical.

By "active derivative" of a monocyanodicarboxylic acid is meant a derivative of such as acid that will react with a diamine to form a polymer according to the invention and includes derivatives such acid chlorides, anhydrides, azides and active esters.

The radical Ar may be aliphatic, alicyclic, heterocyclic or aromatic or mixtures thereof and may include oligomeric and polymeric radicals. Preferably, Ar is an aromatic radical and, more particularly, is a radical derived from a benzene dicarboxylic acid or a polyaromatic dicarboxylic acid containing at least two aromatic units which are either linked directly together or are linked by -CO-, -SO-, -S02-, -O-, -C(CH3)2- or other aliphatic group. By 1directly linked together" is meant that the aromatic units are linked by a direct link between the rings as in biphenylene or terphenylene or are linked in a polynuclear aromatic system as in naphthalene, anthracene and phenanthracene.

The radical R may be aliphatic, alicyclic, heterocyclic or aromatic or mixtures thereof and may include oligomeric and polymeric radicals. For preferred polymers, R is a divalent aromatic radical selected from 1,3- or 1,4- phenylene or from a polyaromatic unit containing at least two aromatic units which are either linked directly together or are linked by -CO-, -SO-, -SO2-, -NH-, -O-, -CH2-, -C(CH3)2or other aliphatic group, "directly linked together" having the same meaning as given above.Typical examples of R include radicals derived from 1,2-diaminoethane, 1,6-diaminohexane, 1,6-diaminocyclohexane, 1,3or 1, 4-diaminobenzene, 1, 8-diaminonaphthalene, 4,4, -diaminobiphenyl, 2,4- or 2,5-diaminopyridine, or 4,4'-diaminodiphenylene-X wherein X may be -CO-, -SO-, -502-, -NH-, -O-, -CH2-, -C(CH3)2- or other aliphatic group. Other examples of diamines from which R may be derived can be found in US-A-3895064 and US-A-4608404. The radical R may be derived from a mixture of diamines.

Preferably, the polymer according to the invention has formula II, ie it is a polyamidoiminoimide. Typical uses for such polymers include fibres, fabrics, mats and papers for thermal insulation; matrices for high performance fibre-reinforced composite materials; as moulding materials either alone or with other materials; wire coatings and films and foils for dielectric uses.

However, the invention includes polymers of formula I, ie polycyanoamides which are the precursors of the polymers of formula II, which find use as adhesives, varnishes, impregnation materials and the like. In such applications, the polycyanoamide is applied to a component as a solution and then subjected to heat to cyclise the cyano group with one of the amide linkages.

Thus, according to another aspect of the present invention, an article comprises a polyamidoiminoimide of formula II formed by the in situ cyclisation of a polycyanoamide of formula I.

The invention also includes a process for the preparation of polymers according to the invention which comprised reacting a monocyanodicarboxylic acid or active derivative thereof in which the cyano group is on a carbon adjacent one of the acid or acid derivative groups with a diamine of formula H2NRNH2, R being as hereinbefore defined.

In a preferred form of the process, the reaction is carried out at temperatures below -100C, more particularly below -150C.

The invention will now be illustrated by reference to the following Examples.

Example 1 2-cyanoterephthaloyl chloride (CTC) (0.5g, 0.0022mole) was dissolved in lOml of benzene and 1,2-diaminoethane (0.13g, 0.0023mole) in lOml of water containing sodium hydroxide (0.09g, 0.0023mole) was added without stirring at room temperature. A polymer film formed immediately at the interface and this was drawn off continuously until the reagents were exhausted. The white polymer was washed with water and dried in vacuum at room temperature (yield 87Z).

Infra-red analysis of the polymer revealed absorption bands at 1730cm-1 and 2220cm-1 confirming the presence of both imide carbonyl groups and nitrile groups in the structure of the polymer indicating that it was partially cyclised, ie it contained repeat units of formula IA and IIA:

The polymer was completely soluble in dimethylformamide.

Example 2 Four polymer samples were prepared by adding CTC (0.5g, 0.0022mole) dissolved in 5ml of solvent (see Table I) dropwise to a stirred solution of 4,4'-diaminodiphenylsulphone (4,4 '-DDS) (0.54E" 0.0022mole) in lOml of dimethylacetamide (DMA) at a temperature of O)C or below (see Table I). After one hour, the reaction mixture was poureS on to cracked ice to precipitate the polymer. The bright yellow polymer was collected by filtration and dried in vacuum (O.lmm Hg) at roas temperature.

TABLE I Solvents for CTC Reaction Temperature Yield Limiting Viscosity No C Z dl/g 1. THF* 0 100 2. THF -10 100 3. DMA -20 100 0.19 4. DMA -20 100 0.30 (@ 5mm Hg) * THF=Tetrahydrofuran The infra-red analysis of polymers 1 to 4 showed a progressive change as the reaction temperature was lowered. Polymers 1 and 2 bdth exhibited absorption bands at 1730cm-1 and 2220cm-1 indicating the presence of both imide carbonyl and nitrile groups, respectively.

Polymers 3 and 4 exhibited only the absorption band at 2220cm-1, the band at 1730cm-1 being virtually undetectable.

A thermogram obtained by differential scanning calorimetry (DSC) of polymer 4 exhibited a broad strong exotherm in the region 200-2500C which was absent from a thermogram obtained by a rerun of the same sample. The exotherm was attributed to a cyclisation reaction and this interpretation was supported by the absence of an infra-red absorption band at 2220cm-1 and the presence of a band at 1730cm-1 in the sample after the first DSC scan. A Tg was not detected below 5000C.

Polymers 1 and 2 were considered to be mixtures of repeat units IB and IIB as shown below. Polymers 3 and 4 were considered to be of repeat unit IB and, for polymer 4 after cyclisation, IIB.

Example 3 Samples of polymers 3 and 4 were compression moulded at 2000C to 2500C and a pressure of 1.6kglmm2 to give transparent yellow discs.

Example 4 Samples of polymers 3 and 4 were subjected to thermogravimetric analysis in oxygen and nitrogen together with samples of commercially available aromatic polyamide and aromatic polyimides, namely Kevlar and Kapton (available from du Pont de Nemours) and Ultem (available from General Electric). The results of the analysis are give in Table II and suggest that the thermooxidative stability of these polymers of the invention is between the stabilities of the aromatic polyamide and the aromatic polyimides.

TABLE II POLYMER TEMPERATURE AT 10Z WEIGHT LOSS OXYGEN (OC) NITROGEN (OC) KEVLAR 385 515 POLYMERS 3 & 4 465 510 ULTEM 561 562 KAPTON 583 > 600 ExamPle 5 Polymers 5 to 10 (see Table III) were prepared. Polymer 5 was prepared in accordance with the method described in Example 2. The remaining polymers were prepared in accordance with the following method which is described with reference to polymer 6.

CTC (0.5g, 0.0022mole) dissolved in 5ml of THF was added dropwise to a stirred solution of 4,4'-DDS (0.54g, 0.0022mole) in 15ml of DMA at a temperature of -200C. After one hour, the temperature was allowed to rise to room temperature and, after a further two hours, the reaction mixture was poured into an ice/water mixture to precipitate the polymer The polymer was collected by filtration and dried in vacuum at rdom temperature.

Details of the polymers are summarised in Table III.

TABLE III Monomers and Yield Limiting Viscosity ratio thereof Z dl/g 5. CTC, 4,4'-DDS (1:1) 94 0.28 6. CTC, 4,4'-DDS (1:1) 90 0.53 7. CTC, 3,3'-DDS (1:1) 92 0.64 8. CTC, DDO (1:1) 96 1.02 9. CTC, DDO (1:0.9) 88 0.61 10. CTC, DDM (1:1) 92 0.55 3,3'-DDS - 3,3'-diaminodiphenylsulphone DDO - 4,4'-diaminodiphenylether DDM - 4,4'-diaminodiphenylmethane Example 6 Strong flexible films of polymer 8 were prepared by dissolving the polymer in DMA, filtering the solution into a small flat glass dish and evaporating the DMA off in an oven at 450C for 48 hours.

Examnle 7 Samples of polymers 7, 8 and 10 were subjected to thermogravimetric analysis in nitrogen similarly to the polymers in Example 4.

The results are suninarised in Table IV.

TABLE IV POLYMER TEMPERATURE AT 10Z WEIGHT LOSS NITROGEN (OC) 3 & 4 (Example 4) 510 7 477 8 510 10 524 Example 8 The mechanical properties of polymer 8, both before and after cyclisation, were determined using an Instron tensile tester on rectangular test pieces (50mm x 5mm x O.lmm) at a cross-head speed of lmm/min at room temperature. The results are summarised in Table V and compared to like properties of other polymers obtained from Polymer Handbook, 2nd Edition, VIII-I.

TABLE V POLYMER YOUNG'S MODULUS ELONGATION AT (GPa) BREAK (Z) 8* 1.67 5.48 8** 2.53 6.11 Polyimide 3.1 5-8 Polyphenylene sulphide 3.3 3.0 Polyphenylene oxide 2.4-2.6 50-100 Polysulphone 2.5 50-100 Nylon 6,6 1.2-2.9 60-300 * before cyclisation.

** after cyclisation.

Example 9 Polymer 8 was subjected to two different curing temperatures for different lengths of time and the resultant cured polymers were subjected to dynamic mechanical analysis using a rheometric solid analyser at a heating rate of 5 C/min. The results are summarised in Table VI.

TABLE 6 CURING TIME VALUE OF E' (GPa) AT 1st TRANSITION 2nd TRANSITION (min) 500C 2500C 3000C ( C) ( C) Polymer cured at 2000C 10 0.82 0.077 - 218 30 2.23 0.425 0.036 228 304 Polymer cured at 2200C 15 2.07 0.383 0.036 220 304 90 2.06 1.18 0.088 250* 318*1 120 2.93 1.91 0.088 *1 320 * diminishing *1 on rescan, this peak shifted to above 3800C *2 disappeared The transition values were taken at maximum tan 8.

The dynamic mechanical analysis trace for the polymer cured at 2200C/ 15min is reproduced as the sole figure accompanying the specification.

As can be seen, surprisingly the polymer appears to regain stiffness above about 3500C and, upon rescanning the sample, no glass transition temperature was observed to the temperature limit of the analyser instrument (4000C). The film sample, after removal from the instrument following this severe thermal cycling, remained flexible.

Claims (9)

1. A polymer comprising a repeat unit of formula I andlor formula II:

wherein Ar is a trivalent organic radical derived from an active derivative of a monocyanodicarboxylic acid in which the cyano group is located relative to one of the acid derivative groups such that imidisation can occur therebetween; and R is a divalent organic radical.

2. A polymer according to claim 1 wherein Ar is an aromatic radical derived from a benzene dicarboxylic acid or a polyaromatic dicarboxylic acid containing at least two aromatic units which are either linked directly together or are linked by -CO-, -SO-, -SO2-, -O-, -C(CH3)2- or other aliphatic group.

3. A polymer according to claim 1 or claim 2 wherein R is a divalent aromatic radical selected from 1,3- or 1,4- phenylene or from a polyaromatic unit containing at least two aromatic units which are either linked directly together or are linked by -CO-, -SO-, -SO2-, -NH-, -O-, -OH2-, -C(CH3)2- or other aliphatic group.

4. A process for the preparation of polymers according to any one of the preceding claims which comprises reacting a monocyanodicarboxylic acid of formula:

or active derivative thereof with a diamine of formula H2NRNH2, Ar and R being as hereinbefore defined in claim

5. A process according to claim 4 wherein the reaction is carried out at temperatures below -100C, more particularly below -150C.

6. A shaped article of a polymer according to any one of claims 1 to 3.

7. An article according to claim 6 wherein the article comprises a polymer of formula II formed by the in situ cyclisation of a polycyanoamide of formula I.

8. A polymer according to claim 1 substantially as hereinbefore described with reference to the Examples and the accompanying drawing.

9. A process according to claim 4 substantially as hereinbefore described with reference to the Examples.