1. Field of the Invention
The invention relates to a process for the production of bismaleinimide derivatives of the formula: ##STR4## wherein R.sub.1 and R.sub.2 are the same or different and each is a C.sub.1 -C.sub.4 -alkyl group, branched or unbranched, and R.sub.3 is a halogen or hydrogen atom starting from maleic acid anhydride and a methylene-bis-aniline.
2. Background Art
The bismaleinimide derivatives of formula I are used, for example, for the production of heat-resistant bismaleinimide resins (Japanese Laid-Open Patent Application No. 61-093159).
A known embodiment for the production of bismaleinimide derivatives is described, for example, in Japanese Laid-Open Patent Application No. 57-159764 (Japanese Patent No. 02-058267). In the process, a methylenebis[N-(monoalkyl)-phenylene]maleinimide] is produced, starting from maleic acid anhydride and a methylene-bis-aniline, in the presence of an acid catalyst. To obtain a pure product with a good yield, a mixture of a halogenated hydrocarbon with an aprotic polar solvent is necessarily used in the process as the solvent. From Comparison Example 2 (page 10) of the above-mentioned application it is known that, if dichloroethane is replaced by toluene in the solvent mixture, both the purity is reduced from 93 to 67 percent and the yield of the desired end product is also reduced from 95 to 88 percent. The substitution of dichloroethane by xylene even reduces both the purity from 95 to 53 percent and the yield of the desired end product from 95 to 64 percent. A major drawback of the process lies in that the environmentally polluting halogenated hydrocarbons have to be used as the solvent in order to obtain a pure end product in a good yield.