FIELD OF THE INVENTION

The present invention relates to novel polyfunctional phthalimides and to a reversibly cross-linked product which can be produced by cross- linking an at least trifunctional non-linear imide, such as a phthali ide, with an at least difunctional amine. The invention also relates to a process for making such a reversibly cross-linked product.

BACKGROUND OF THE INVENTION

Reversibly cross-linked polymeric products are known in the prior art. By reversibly cross-linked is meant that, upon heating, the cross¬ links in the polymer are broken and then by subsequent cooling the cross-links are reformed. These materials are also called, "thermally reversible polymers." This property is useful since it provides the opportunity to work the material in a low viscosity form and then obtain a polymer with good physical properties merely by cooling the material to ambient temperature.

One of the first examples of thermally reversible cross-links is found in U.S. patent 3,435,003 where polymer backbones comprising pendant furan groups are reacted with maleimides to produce materials useful as plastics and as adhesives. These materials can be reformed by heating to a temperature of 120-140°C. Different types of polymer backbones are possible including polyamide, polyester, polyurea and polyurethane.

Another type of thermally reversible cross-link is disclosed in U.S. patent 3,678,016 where cross-linking of cyclic anhydrides with

hydroxyl groups or secondary amines, or carboxylic acid groups with CH2=CH0- groups by chemical addition reaction, is disclosed. Also disclosed is the ability to fluidize the composition by heating, reforming the composition and cooling to recrosslink the composition.

Still another type of thermally reversible cross-link is disclosed in U.S. patent 3,872,057 where cross-linking is achieved by dimerization of nitroso groups. At higher temperatures the nitroso di ers dissociate so that the composition can be melt fabricated. Upon cooling the dimers reform to give a cross-linked product. These materials are workable at temperatures above 75°C.

The article, "Thermally Reversible Polymer Linkages. 1. Model Studies of the Azlactone Ring," Wagener, K.B., et al., Macromolecules, Vol. 24, No. 6, 18 March 1991, discloses thermally reversibly polymers made from an azlactone and a nucleophilic material such as a phenol. Thermal reversibility in the temperature range of 20O-300°C can be achieved with this system. The article further states that, due to the covalent nature of this type of cross-link, polymers with good mechanical integrity can be obtained.

Despite the fact that several thermally reversible cross-linking systems exist, there remains a need in the art for a reversibly cross¬ linked product that is workable at a temperature below 300°C and which, at ambient temperatures, has sufficient mechanical integrity and chemical resistance for use in a variety of applications. Existing systems are also generally too expensive for practical application.

Further, many of the aforementioned reversibly cross-linked systems also suffer from the disadvantage that upon heating to decrosslink, they undergo unwanted side reactions thereby effectively limiting their reversiblity.

Accordingly, it is the primary object of the present invention to provide a reversibly cross-linked polyamide which can be worked at a temperature in the range of 100-300°C. It is a further object of the present invention to provide a reversibly cross-linked polyamide which does not undergo significant side reactions upon decrosslinking. It is a still further object of the present invention to provide novel polyfunctional phthalimides which can be used to make reversibly crosslinked polymers. These and other objects of the invention will be apparent from the summary and detailed description which follow.

SUMMARY OF THE INVENTION

In its first aspect, the present invention relates to polyfunctional phthalimides having novel properties which make them particularly suitable for the production of reversibly crosslinked polymers. These polyfunctional phthalimides can be represented by the following formula (I):

wherein n is an integer greater than 4; K , R , R3 and R4 are independently selected from hydrogen, C^-Cio linear or branched alkyl, halogen, 4-C18 aryl , C7-C20 alkaryl, C5-C20 aralkyl, C3-C18 cycloalkyl, nitro and cyano radicals; X is selected from SO2, C=0, CH2 and C=S; and D is a polyvalent linear or branched radical selected from C2-C50 alkyl, C3-C50 cycloalkyl, C3-C50 polycycloalkyl , C6-C50

aryl, C7-C50 alkaryl, C7-C50 aralkyl radicals and oligomers of one or more of these radicals, all of which may be optionally substituted with one or more non-interfering substituents.

By non-interfering substituents is meant substituents which do not interfere in the process for making reversibly crosslinked polymers from the materials of the formula I and which do not interfere with the reversible crosslinking of the resultant polymers.

Some polyfunctional phthalimides containing more than 4 phthalimide groups per molecule are known in the art. For example, Chemical Abstract Registry numbers 120233-26-3, 139656-81-8, 142960-22-3 and 142960-23-4 are all compounds containing at least 5 phthalimide groups therein. However, none of these compounds meet the definition of the formula I above and they are all thus outside the scope of the present invention.

It is known to react imides with amines from, for example, U.S. patent 2,323,054 which discloses the condensation of imides of dicarboxylic acids with amines containing at least two primary or secondary a ino groups at elevated temperature. Further, U.S. patent 3,883,486 prepares polyamides by the reaction of polyamines and oligomers possessing imide groups. The imide group-containing oligomers are made by the reaction of an oligomeric polyamine with an anhydride of which at least 60 mole percent contains a linear or cyclic radical possessing an ethylenically unsaturated group.

U.S. patent 4,731,436 discloses the preparation of a thermosetting cross-linked imide resin from the reaction of an polyamine with an N,N'-bisimide of an unsaturated dicarboxylic acid. Further, U.S. patent 4,808,695 teaches the preparation of a cross-linked polyamide by the reaction of a polyi ide with a polyamine. The cross-linked products are useful as the matrix in high performance composites.

None of the foregoing references even suggest the possibility that a reversibly cross-linked product can be prepared by the reaction of a polyfunctional imide compound with a polyamine. Accordingly, it has surprisingly been found that such a reversibly cross-linked product can be prepared from these reactive groups.

In a second aspect, the present invention relates to a reversibly cross-linked product produced by the reaction of a non-linear polyimide reactant having an imide functionality of at least three and a polyamine comprising at least two primary or secondary amino functionalities. The product is characterized by the fact that, at a temperature in the range of 50-300°C, at least some of the product de- crosslinks to provide a fluid material.

This de-crosslinking can be observed as a change in the viscosity of the polymeric material by at least a factor of 100 in a temperature range of 50°C. This temperature range of 50°C in which the decrosslinking occurs is always above the glass transition temperature of the polymeric product and tops out at a maximum temperature of 300°C. Further, the viscosity change is observed either upon heating the polymeric material from a room temperature through the 50°C temperature range or by cooling the polymeric material from 300°C through the 50°C temperature range.

In a third aspect, the present invention relates to a process for the production of a reversibly cross-linked product comprising the step of cross-linking a non-linear polyimide reactant having an imide functionality of at least three, with a polyamine comprising at least two primary or secondary a ine functionalities. This process produces a reversibly cross-linked product, which at a temperature in the range of 50-300°C at least partially de-crosslinks to provide a fluid material .

By functionality is meant the average number of imide groups in one mole of the polyimide or the average number of amine groups in one mole of the polyamine.

The product of the present invention has the advantage that, upon heating, it can be formed into the desired configuration due to its low viscosity at a temperature in the range of 50-300°C, and then, simply by cooling, a solid polymeric product with good physical properties is obtained.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In its first aspect, the present invention relates to polyfunctional phthalimides of the formula I:

wherein n is an integer greater than 4; R , R , R3 and R4 are independently selected from hydrogen, CI-CIQ linear or branched alkyl, halogen, C4-C18 aryl, C7-C20 alkaryl, C5-C20 aralkyl, C3-C18 cycloalkyl, nitro and cyano radicals; X is selected from SO2, C=0, CH2 and C=S; and D is a polyvalent linear or branched radical selected from C2-C50 alkyl, C3-C50 cycloalkyl, C3-C50 polycycloalkyl , C6-C50 aryl, C7-C50 alkaryl, C7-C50 aralkyl radicals and oligomers of one or more of these radicals, all of which may be optionally substituted with one or more non-interfering substituents.

For R1-R4, what is meant by a C4 aryl is that one of R1-R4 can combine with the aromatic ring to form a naphthalene-like aromatic structure with a total of 10 carbon atoms.

More particularly, the group D may optionally be subsituted with the following non-interfering substituents: oxygen, nitrogen, silicon, silicon dioxide, sulphur, sulphone, all of which radicals may also be optionally substituted at one or more of the atoms in the radical with a substituent selected from silicon dioxide, amido, azo, azino, azoxy, alkoxy, hydroxy, sulphur, SO2, nitro, nitroso, anilino, cyano and halogen groups.

In the more preferred embodiments of the phthalimides of the present invention, n is at least 8, R1-R4 are preferably selected from hydrogen and C1-C4 alkyl and D is an unsubstituted epoxy residue selected from alkyl, alkaryl, aralkyl, cycloalkyl, polycycloalkyl and aryl radicals. Examples 1-9 of the present application exemplify some of the more preferred phthalimides of the invention and how to make them.

In a second aspect, the present invention relates to a reversibly cross-linked product produced by the reaction of a non-linear polyimide reactant having an imide functionality of at least three and a polyamine comprising at least two primary or secondary amino functionalities. The product is characterized by the fact that, at a temperature in the range of 50-300°C, at least some of the product de- crosslinks to provide a fluid material.

This de-crosslinking can be observed as a change in the viscosity of the polymeric material by at least a factor of 100 in a temperature range of 50°C. This temperature range of 50°C in which the decrosslinking occurs is always above the glass transition temperature

of the polymeric product and tops out at a maximum temperature of 300°C. Further, the viscosity change is observed either upon heating the polymeric material from a room temperature through the 50°C temperature range or by cooling the polymeric material from 300°C through the 50°C temperature range.

Typical polymers exhibit a slight decrease in the viscosity upon heating but generally this decrease is far less than a factor of 100. More details about standard polymer viscosity behavior can be found in, "Properties of Polymers," B.W. van Krevelen, Elsevier Science Publications B.V., 3rd Edition (1990).

More preferably, the polyimide reactant employed to make the reversibly cross-linked product of the present invention is derived from an dicarboxylic acid anhydride. The preferred dicarboxylic acid anhydrides for this purpose are phthalic anhydride, substituted phthalic anhydrides and sulphone imides.

The polyimide must be non-linear and thus it must contain more than two imide groups per mole and these imide groups cannot be pendant on a linear polymer backbone. Preferred imides for use in the present invention contain at least three imide groups attached to a single radical in a non-linear arrangement. Most preferably, these materials are star-shaped (i.e. at least octafunctional) .

One method for making the polyimide is to react the carboxylic acid anhydride with an at least tetrafunctional amine to produce an at least tetrafunctional imide. Another possibility is to produce, for example, a bisimide containing a reactive group in the difunctional linking group and then subsequently reacting this bisimide with an at least difunctional compound to thereby produce a compound containing several bisimide functionalities.

An example of the second route to the polyimide is to react phthalic acid anhydride with diethylene triamine in a molar ratio of 2:1 to produce an bisimide linked by an amino-functional radical. This bisimide can then be subsequently reacted with a polyfunctional epoxide or isocyanate, for example, to produce a non-linear, polyfunctional imide. A detailed example of this route can be found in Example 1.

Useful polyfunctional epoxides include bis-(2,3-epoxypropyl) bisphenol A, tris-(2,3-epoxypropyl)-p-aminophenol , tris-(2,3-epoxypropyl) cyanuric acid and N,N,N' ,N'-tetra-(2,3-epoxypropyl ) methylene dianiline. A useful diisocyanate is diphenyl methane diisocyanate and a useful triisocyanate is tris-(6-isocyanatohexyl)isocyanurate.

The polyimide is cross-linked with a polyamine to form a polyamide. The polyamine must have at least two primary and/or secondary amino groups in order to accomplish the cross-linking reaction. Useful polyamines include hexamethylene diamine, xylylene diamine, bis-(3-aminopropyl) amine and tris-(2-aminoethyl) amine.

The polyamine and the polyimide are mixed together at an elevated temperature of from 50-300°C, more preferably 100-250°C, and, upon cooling, form a cross-linked product. The rate of cooling influences the cross-link density and thus a slow cooling is preferred since this favors the cross-linking reaction.

The reversibly cross-linked products of the present process are preferably products that can be de-crosslinked, to produce a one hundred fold viscosity reduction in a temperature range of 50°C and this range being in the temperature range of from 50-300°C. More preferably, the de-crosslinking occurs in a temperature range of from 100-250°C to make processing of the polymeric material possible at slightly lower temperatures.

The reversibly cross-linked products of the present invention are useful in composites, coatings, as sealants, for the filling of cracks, as hot-melt adhesives and for making shaped objects, among other uses.

Examples A-J and 1-9

Synthesis of polyfunctional phthalimides

Examples A-H are synthesis examples for the synthesis of phthalimides which are outside the scope of the invention but can be used to make reversibly cross-linked polymers within the scope of the invention as shown in Examples 13-29. Examples 1-9 are examples for the synthesis of phthalimides within the scope of the present invention.

Example A - Synthesis of Bis-(2-phthalimido ethyl) amine

In a 1 liter, three-neck flask provided with a s.s.-stirrer, a nitrogen inlet and a dropping funnel, 592.5 grams (4.0 moles) of phthalic anhydride was melted in a nitrogen atmosphere. Then, 218 ml (2.0 moles) of diethylenetriamine was added with stirring over a 30 minute period at 137-160°C. After a further 10 minutes, the heat of reaction had raised the temperature to 190°C which then returned to 160°C due to the production of water as a by-product of the reaction. Heating and evaporation of water was continued for one hour whereafter the liquid residue was poured on an aluminum sheet. The product was recrystallized from 3 liters of 2-methoxyethanol yielding 673.4 grams (92.7%) of white crystals with a melting point of 180-181°C and having a purity, measured by HPLC, of 98.8%.

Example B - Synthesis of Bis-(3-phthalimido propyl) amine

Using the procedure of Example A, phthalic anhydride was reacted with bis-(3-aminopropyl ) amine. The corrresponding bis-phthalimide was obtained having a purity of 97.4% (HPLC) and a melting point of 134-135°C.

Example C - Synthesis of Bis-(3-methylphthalimido ethyl) amine

Using the procedure of Example A, 3-methyl phthalic anhydride was reacted with diethylene diamine. After recrystallization from ethanol , the product had a melting point of 120-121°C.

Example D - Synthesis of Bis-(2-dichloro phthalimido ethyl) amine

1 mole of diethylene triamine was added to a solution of 2 moles of 2,3-dichlorophthalic acid in N-methyl pyrrol i done. After heating of the solution at 180°C for 2 hours and subsequent cooling, the precipitate was filtered off and recrystallized from dioxane to give a product with 99% purity (HPLC) and a melting point of 201-203°C.

Example E - Synthesis of Tris-(2-phtha1imido ethyl) amine

An equivalent amount of tris-(2-aminoethyl ) amine was added to a solution of phthalic anhydride in dimethyl aceta ide (DMA). Then, the solution was stirred for 1 hour at room temperature followed by 2 hours at reflux temperature (145°C). Upon cooling, the product crystallized and was purified by washing with alcohol to give a yield of 78% of a product with a melting point of 191-192°C.

Example F - Synthesis of Tris-(6-phthalimido hexyl) isocyanurate

Tris-(6-isocyanatohexyl) isocyanurate was obtained by distillation of Tolonate ^® HDT (ex. Rhone Poulenc) using a short-way distillation apparatus (KDL - ex. Leopold). According to GPC, the distillate was very pure and contained only 2% of hexamethylene diisocyanate as impurity. The distillate was added to a solution of phthalic acid in DMA at 50°C and after the CO2 emission had ceased, the solution was heated to reflux temperature. After two recrystallizations from DMA/ethanol , the product contained 88% of the desired compound.

Example G - Synthesis of N,N,N' ,N'-tetrakis-(2-phthalimido ethyl) diaminoethane

A mixture of 111 grams (0.30 mole) of the product of Example A, 13 ml (0.15 mole) 1,2-dibromoethane, 25 gr. (0.18 mole) potassium carbonate and 750 ml of DMA was stirred under reflux for 21 hours. Evaporation of the solvent and repeated recrystallization from chloroform/ethanol produced 23.7 grams (20.6%) of yellow crystals with a melting point of 193-200°C. According to TLC and NMR, the product was essentially pure.

Example H - Synthesis of N,N,N' ,N'-tetrakis-(2-phthalimido ethyl) terephthalic diamide

29.9 gr. of terephthaloyl dichloride and 100 gr. of the product of Example A were refluxed in 600 ml toluene for 23 hours. After cooling, the reaction product was filtered to yield 112 gr. (95%) of white crystals with a melting point above 300°C. The structure was confirmed by

Example I - Synthesis of the coupling product of the product of Example A with diphenyl methane diisocyanate

A mixture of 100 gr. (0.28 mole) of the product of Example A, 34.5 gr. (0.14 mole) of diphenyl methane diisocyanate and 600 ml of dimethyl formamide was heated for 2 hours at 100°C and quenched in ethanol , whereafter the solvents were removed by evaporation. After drying for 2 days under vacuum at 130°C, 138 gr. (102.7%) of a white powder still containing some dimethyl formamide, was obtained. The product had a melting point of 193-196°C and the structure was confirmed by NMR.

Example J - Synthesis of the coupling product of the product of Example A with bis-(2,3-epoxypropy1) bisphenol A

A mixture of 2 moles of the product of Example A and 1 mole of bis-(2,3-epoxypropyl) bisphenol A was heated to 200°C for 0.5-1 hour. The resulting yellow-colored reaction product was poured out on an aluminum sheet. After cooling, a hard, brittle product was obtained. GPC (PL-100 column) revealed a nearly complete conversion and NMR confirmed the structure of the product.

Example 1 - Synthesis of the coupling product of the product of Example A with tris-(2,3-epoxypropyl)-p-amino phenol

A mixture of 3 moles of the product of Example A and 1 mole of tris-(2,3-epoxypropyl)-p-amino phenol was heated to 200°C for 1 hour. After cooling a brittle dark brown product resulted.

Example 2 - Synthesis of the coupling product of the product of Example A with tris-(2,3-epoxypropyl ) cyanuric acid

Following the procedure of Example 3, this product was produced using 3 moles of the product of Example A and 1 mole of tris-(2,3-epoxypropyl) cyanuric acid.

Example 3 - Synthesis of the coupling product of the product of Example B with tris-(2,3-epoxypropyl) cyanuric acid

Following the procedure of Example 3, this product was produced using

3 moles of the product of Example B and 1 mole of tris-(2,3-epoxypropyl) cyanuric acid.

Examples 4-9 - Synthesis of Octafunctional Phthalimides

Octafunctional phthalimides were obtained by heating one mole of tetrafunctional epoxide in the presence of 4 moles of a bis- phthal imidoal kyl amine at 200°C for 1 hour. Details of the different phthalimides can be found in Table 1 below.

Table 1 Example Bisphthal imide Epoxide

4 Example A A

5 Example B A

6 Example C A

7 Example D A

8 Example A B

9 Example B B Epoxide A is N,N,N' ,N' ,-tetrakis-(2,3-epoxypropyl)methylene dianiline (Araldite® MY-721, ex. Ciba-Geigy).

Epoxide B i s

0 0 / \ / \

H ₂ C - CH - CH ₂ - - CH ₂ - CH - CH ₂

H ₂ C - CH - CH ₂ - - CH ₂ - CH - CH ₂

Exampl e 10

Preparation of a thermally reversible cross-linked product in accordance with the present invention.

Diethylene triamine was reacted with two equivalents of phthalic acid anhydride at a temperature of 220°C to produce an amino functional bisimide. This amino functional bisimide was then further reacted with a tetrafunctional epoxide at a temperature of 220°C using four equivalents of bisimide per mole of tetrafunctional epoxide to produce an octafunctional imide compound. This octafunctional phthalimide was then reacted at elevated temperature with hexamethylene diamine using a stoichio etric excess of the imide. Upon gradual cooling, a cross¬ linked product is obtained which, upon reheating demonstrates the viscosity behavior shown in figure 1, curve B. Also shown in figure 1, curve A is the viscosity behavior of a typical thermoplastic polymer in order to demonstrate the difference between the material of the present invention and a thermoplastic polymer. From figure 1, the more than 100 fold viscosity decrease within a 50°C temperature range of the polymer of the present invention can be seen. The polymer of this example exhibited, when cooled to room temperature a Shore D hardness of 83.

Examples 11-27

Production of Various Reversibly Crosslinked Resins

Several reversibly crosslinked resins in accordance with the present invention were obtained by reacting polyfunctional phthalimides- with less than a molar equivalent of an amine and heating to 200-230°C until a homogeneous liquid is obtained. The crosslinked product is formed by gradually cooling at a rate of about 1°C per minute.

In Table 2 a number of reversibly crosslinked resins and their glass transition temperatures are given.

Table 2

TAA is tris-(2-aminoethyl) amine HMDA is hexamethylene diamine XDA is xylylene diamine BAPA is bis-(3-aminopropyl) amine

Example 28 - One Pot Procedure to Make Reversibly Crosslinked Resin

1 mole of diethylene triamine was added to 2 moles of molten phthalic anhydride. Heating was effected until 220°C in order to melt the entire mixture. In time, water evaporated from the mixture. When water formation ceased, 0.25 mole of Araldite® MY-721 was added over 10 minutes at 180°C. After one hour at 180°C, 0.75 mole HMDA was added and heating with stirring was continued at a temperature of 220°C until an homogeneous, low viscosity liquid was obtained. This mixture was gradually cooled to room temperature to yield 97.7% of the same resin as obtained in Example 19.

The foregoing detailed description and examples of the invention have been presented for the purposes of illustration and description only and are not to be construed as limiting the invention in any way. The scope of the invention is to be determined from the claims appended hereto.