Complete specification

One pot synthesis of Bismaleimide derivatives

Field of Invention:

The present invention relates to the synthesis of bismaleimide derivatives, more particularly to one pot synthesis of bismaleimide derivatives using diamine and maleic anhydride in the presence of a suitable acid catalyst.

Background of the Invention:
Bismaleimides are an important class of thermosetting polyimides widely used as high performance composite matrices. As compared with other thermosetting polyimides, bismaleimides display excellent processability, high performance, and low cost; thus they have been selected as attractive candidates for advanced composite matrices.

Bismaleimide resins (BMIs) have gained much attention as being heat resistant polymers and can be used in composites formulations because of their excellent thermal stability after curing. Bismaleimide resins can be used at elevated temperature (2000 -300°C) and possess better thermal stability, flame resistance and retention of mechanical properties at high temperatures over epoxy resins. Epoxy resins usually cannot withstand the severe environment of surface mount technology (260°C, 30 s). Hence the bismaleimides bridge the temperature performance gap between the epoxy resins and polyimides.
Bismaleimides are low molecular substances containing imide structures with monomer form which can undergo polyaddition reaction by themselves as well as with other co-monomers. The monomers are usually synthesized from maleic anhydride and an aromatic or aliphatic diamine; the bismaleimic acid formed during the reaction is cyclodehydrates to obtain a bismaleimide resin. Bismaleimides prepared from parent aromatic diamines and maleic anhydride, are usually solid at room temperature and are cured at above 200°C The double bond of the maleimide is very reactive and can undergo chain extension reaction (polymerization) via multiple carbon-carbon bond formation at higher temperature (150 - 250 °C) without evolving any volatiles to give highly crosslinked rigid polymer network. The polyaddition reactions of bismaleimide results three dimensional crosslinked network structures which imparts high temperature resistance.

Bismaleimides are very useful matrix resins for high temperature application since they possess superior thermo mechanical properties viz. high crosslinking ability, high glass transition temperature, high thermal and thermooxidative stability, excellent dielectric property, humidity resistance, corrosion resistance, high char yield, excellent fire resistance, resistance to solvents, specific strength, tensile strength and specific modulus and low water absorption.

Owing to its high performance-to-cost ratio, excellent processability, balance of thermal, electrical and mechanical properties, bismaleimides (BMIs) have become one of the important high performance thermosetting engineering plastic and structural composites in various applications such as, aero-engines, military aircraft, multilayer printed circuit boards for large scale computers, fibre reinforced advanced composite materials in aviation and space industries, structural adhesives and plastic modifier, potting resin, and also used as an intermediate for the synthesis of cross-linking agents, pharmaceuticals, pesticides, antiseptics and crystalline adducting agents.

The present invention provides a simple one pot cost competitive methodology for the synthesis of bismaleimide derivatives with minimum cycle time. Further the methodology developed yields high purity products which possess high heat resistance, high thermal stability, low moisture absorption, good mechanical and dielectric properties.

Objective of the Invention:
The main objective of the present invention is to provide a simple one pot methodology for the synthesis of bismaleimide derivatives.

The second objective of the present invention is to reduce the cycle time and cost involved in the synthesis of bismaleimide derivatives.

Another objective of the invention is to provide a simple and facile bismaleimide synthesis methodology that yields high purity products with excellent thermal, electrical and mechanical properties.

Brief description of the prior art:
EP0318162A2 discloses the synthesis of novel bismaleimide derivatives formed in two steps by reacting oxyethylene diamines and maleic anhydride to form bismaleic acid which is reacted with acetic anhydride in the presence of acetone to form the bismaleimide. This is further reacted with high molecular weight
polyoxyalkyleneamine to produce a novel bismaleimide derivative.

JP1211563A discloses a method for production of bismaleimide by reacting a diamine with maleic anhydride in a mixed solvent of an aromatic hydrocarbon or a halogenated hydrocarbon and an aprotic polar solvent at 150°C to give a bismaleamic acid, subjecting the bismaleamic acid to ring closure through dehydration in the presence of an acid catalyst at 200°C and finally distilling away the formed water in an azeotropic state to provide a high-purity bismaleimide. The obtained bismaleimide is used as laminate material, electrical insulating material, adhesive, etc.

JP2306960A provides bismaleimide compound and their production methods that involve subjecting the diamines and maleic anhydride to condensation reaction in an organic solvent at 0-100°C for 1-lOhr to obtain bismaleamic acid, further the bismaleamic acid is subjected to ring-closing reaction with dehydration in presence of a catalyst to obtain 4,4'-diamino-triphenylamine which is used as synthetic intermediate for thermosetting resin having excellent heat resistance and flexibility.

CN1775775A relates to a method for preparing bismaleimide compound reacting diamine with maleic anhydride in an organic solvent, catalyst and under the effect of a polymerization inhibitor in a homogeneous reaction conditions and involves direct synthesis of bismaleimide compound by catalytic dehydration ring-closure reaction. Further the said method includes several washing, filtering and drying steps to obtain the final bismaleimide compound making the process a time consuming one.

JP62099358A discloses a novel bismaleimide compound namely HN'-S/S'-dimemyl^^'-diaminodiphenylmethane with excellent storage stability, water-resistance and workability. The said bismaleimide compound is produced by reacting diamine with maleic anhydride in an organic solvent and subjecting the resultant amic acid to dehydrative cyclization in the presence of an acid catalyst. The novel bismaleimide compound is useful as a resin material such as laminated sheet, fiber reinforced composite material, sliding material, molding material, sealant and protective paint for electronic part, resist material, electrically conductive paste, etc.

JP62221668A provides a method for production of bismaleimide compound in high yield without producing polymeric by-products. The method involves heating the maleic anhydride and an aromatic or aliphatic diamine in an organic solvent in the presence of an ion-exchange resin at a temperature of 50 -160°C to effect dehydrative cyclization reaction. An alternative method is also proposed, which involves reacting maleic anhydride with an aromatic or aliphatic diamine to obtain bismaleamic acid and subjecting it to dehydrative cyclization without separating the amic acid from the reaction system.
Yuan et al., (2006) in "Homogeneous Synthesis of N,N'-(4,4'-Diphenylmethane) Bismaleimide" reported a single step process for the synthesis of N,Nl-(4/4'-Diphenylmethane) Bismaleimide by reacting 4,4'-diaminodiphenylmethane with maleic anhydride in homogeneous phase. The water formed is eliminated through azeotropic distillation. The reported yield of the resulted product was 86 % by wt and its purity was found to be 98.3%.

All of the above mentioned methods for the production of bismaleimide compounds involve time consuming multi step reactions utilizing numerous chemical reagents such as solvents, catalysts, inhibitors, etc that produces side products thus affecting the purity and yield of the final product and also pollute the environment. The present invention eliminates the drawbacks of the existing production methods by presenting a simple and facile one pot synthesis of bismaleimide derivatives involving less cycle time with reasonable cost competitive methodology. The present invention further provides high product yields with excellent purity under favorable experimental conditions.

Summary of the invention:
The present invention provides a simple and facile one pot synthesis of industrially valuable and commercially potential bismaleimide derivatives. Bismaleimides resins are widely used thermosetting materials in various industrial and engineering applications. A new route for the synthesis of bismaleimide derivatives by one pot approach involves reacting stoichiometric quantities of diamine and maleic anhydride in a suitable organic solvent; adding a calculated amount of acid catalyst and a dehydrating agent to the reaction mixture; maintaining the reaction mixture at a desired temperature and time for completion of the reaction; the resulting crude product is filtered and washed to remove acidic impurities; and finally the crude product is recrystallized to obtain the final bismaleimide derivative. The resulting bismaleimide derivatives are excellent purity with high yield. Further the present one pot synthesis provides a less cycle time with reasonable cost competitive methodology for the production of bismaleimide compounds with excellent thermal, electrical and mechanical properties.

Detailed description of the invention:
The present invention relates to the synthesis of industrially valuable and commercially potential bismaleimide derivatives. Bismaleimides resins are widely used thermosetting materials in various industrial and engineering applications. The present invention provides a simple and facile one pot synthesis of bismaleimide derivatives with high yield and excellent purity under favorable experimental conditions. The present invention further provides less cycle time with reasonable cost competitive methodology for the production of bismaleimide compounds.

Synthesis of bismaleimide (BMI) derivatives:
A new route for the synthesis of bismaleimide derivatives by one pot approach involves reacting appropriate derivatives of amines and maleic anhydride in the presence of a suitable acid catalyst as detailed below:

A novel one pot synthesis of bismaleimide derivatives comprises of following steps:
a) reacting the stoichiometric quantities of diamine and maleic anhydride in a suitable organic solvent;

b) adding a calculated amount of acid catalyst and a dehydrating agent to the reaction mixture;
c) maintaining the reaction mixture at a desired temperature and time to complete the reaction;
d) the resulting crude product is filtered and washed to remove acidic impurities; and
e) finally the crude product is recrystallized to obtain the final bismaleimide derivative.
In the preferred embodiment the diamine used includes both aromatic and aliphatic ether linked diamine.
In the preferred embodiment the organic solvent is selected from dimethylformamide, dimethyllacetamide, dimethyl sulfoxide and mixtures thereof.

In the preferred embodiment the acid catalyst used is sulfuric acid.

In the preferred embodiment the dehydrating agent used is phoporous pentoxide.

In the preferred embodiment the novel one pot synthesis of bismaleimide derivatives yields products with 95.23% purity and 95 % yield.

Example 1
150 ml of dimethylformamide (DMF) is charged into the two necked round bottomed flask equipped with reflux condenser. Stoichiometric quantities of diamine and maleic anhydride is added to the DMF and stirred for 30 minutes. The reactants are cooled to 0 - 5°C followed by adding slowly 28.6 gm of Phosphorus pentoxide (P2O5) and 14.8 gm of sulfuric acid (H2SO4) to the reaction mixture. Temperature of the reaction mixture is maintained at 0-5°C for 30 minutes with constant stirring and subsequently the temperature of the mixture is raised to 70-80°C and kept for 3 hours. Then the reaction product is cooled to room temperature and quenched in excess amount of ice water. The resulted crude product is filtered and thoroughly washed with water, followed by sodium bicarbonate to remove acidic impurities. Finally the resulting crude product is recrystallized with 1:1 ethanol and water to obtain the final bismaleimide derivative.

We Claim:

1. A simple and facile one pot synthesis of bismaleimide derivatives with high yield and excellent purity comprises of:

a) reacting the stoichiometric quantities of diamine and maleic anhydride in a suitable organic solvent;

b) adding a calculated amount of acid catalyst and a dehydrating agent to the reaction mixture;

c) maintaining the reaction mixture at a desired temperature and time to complete the reaction;

d) the resulting crude product is filtered and washed to remove acidic impurities; and

e) finally the crude product is recrystallized to obtain the final bismaleimide derivative.

2. As claimed in claim 1, wherein the said diamine includes both aromatic and aliphatic ether linked diamine.

3. As claimed in claim 1, wherein the said organic solvent is selected from dimethylformamide, dimethyllacetamide, dimethyl sulfoxide and mixtures thereof.

4. As claimed in claiml, wherein the said acid catalyst is sulfuric acid.

5. As claimed in claiml, wherein the said dehydrating agent is Phosphorus pentoxide.

6. As claimed in claiml, wherein the product yield of the said process is 95%.

7. As claimed in claiml, wherein the purity of bismaleimide derivatives obtained from the said process is 95.23%.