Bisdichloromaleimide

Six bisdichloromaleimides having different aromatic structures were prepared by reacting 2,3-dichloromaleic anhydride with (a) 1,5-diaminonath-thalene, (b) bis(m-aminophenyl)methylphosphine oxide,... 

Polymerization of these bisdichloromaleimides was carried by nucleophilic displacement of chlorine with 9,9-bis(p-aminophenyl)fluorene. The resulting polymers were characterized by IR spectroscopy and reduced viscosity measurements. Anaerobic char yields of these polymers at 800°C ranged from 55-60%. In presence of air, a complete loss of weight was observed between 600-650 C. Thermal cross-linking of these polymers was also investigated. 

The bisdichloromaleimides thus obtained may be polymerized thermally by the opening of the double bond. Such cross-linking... 

Nucleophilic substitution reactions have been effectively exploited in the synthesis of several classes of polymers. However, only scanty reports are available on the application of such reactions to the displacement of chlorine in bisdichloromaleimides, although several examples of displacement of chloride by nucleophiles in N-substituted dichloromaleimides exist in literature. Amines (5), phenols (6), and alcohols and thiols (7) have been used as nucleophiles in such reactions. 

Relies and Schluenz (8) have reported the preparation of poly(maleimide-ethers) by using bisphenols and bisdichloromaleimides. These polymers were soluble in dimethylformamide (DMF) and dimethylsulfoxide (DMSO) and gave tough flexible films. Phosphorus-containing poly(maleimide-amines) have been reported to have poor thermal stability and little flame retardation (9). 

In the present work, condensation polymerization of bisdichloromaleimides was carried out with 9,9-bis(p-aminophenyl) fluorene. 

The reaction of diamines and bisdichloromaleimides proceeds with the displacement of one chlorine. The resulting poly(maleimide-amine) contain double bonds as well as chlorine in the backbone. The presence of double bonds in the backbone of these polymers also makes them susceptible to cross-linking reactions which may be initiated by heat. 

Preparation of Bisdichloromaleimides. The method of Martin et al. (14) was used for the preparation of bisdichloromaleimides. Diamines (0.005 mole) and 2,3-dichloromaleic anhydride (0.01 mole) were separately dissolved in glacial acetic acid and the solutions were then mixed and heated slowly to reflux temperature. After refluxing for 2 h, the solutions were cooled, and bisdichloromaleimides were precipitated in water. The products were filtered and washed with water until free of acetic acid. After drying, the products were recrystallized from toluene/hexane. 

Preparation of Polymers. The polymerization of the above prepared bisdichloromaleimides was carried out according to the method of Relies and Schluenz (8). The 9,9-bis(p-aminophenyl) fluorene (0.001 mole) was dissolved in 10 ml of freshly distilled DMF containing 0.002 mole of triethylamine as an acid acceptor. 

Characterization. Infrared spectra of bisdichloromaleimide monomers and polymers in KBr pellets were recorded, using a Perkin-Elmer 180 spectrophotometer. Elemental analyses were provided by Huffman Laboratories. Mass spectra were recorded at 70 eV on a Hewlett-Packard MS 5980 instrument by the direct inlet procedure. A DuPont 990 thermal analyzer was used to evaluate thermal behavior of bisdichloromaleimide monomers and polymers. Reduced viscosity of the polymers was determined in DMF at 30°C with a Cannon viscometer. Thermal polymerization was studied by heating a known weight of the material from room temperature to the desired temperature in a glass tube. The extent of curing was evaluated by extraction with DMF at room temperature. 

Characterization of Bisdichloromaleimides. Physical description, molecular weight, and analytical data of the monomers are given in Table I. Melting points of these monomers were above 250°C. Thus, in compounds (b), (c), and (f) in Table I, endothermic transition associated with melting was observed in DSC at... 

It was, therefore, decided that we would study thermal polymerization of bisdichloromaleimides at 300°C for 30 min. The resulting product was soluble in DMF to a great extent (Table III) with the exception of compound (b). This indicates the absence of thermal polymerization under these conditions. Anaerobic char yields of these thermally treated bisdichloromaleimides depended on their backbone structure a very low value was obtained in compounds (a) and (c) compound (b), which contained phosphorus, was most stable. Condensed phase reactions are influenced by the presence of phosphorus in these polymers. An almost linear relationship is observed between anerobic char yields at 800°C and bridge formula weight of bisdichloromaleimide (Fig. 3). 

Table III. Anerobic Char Yields of Bisdichloromaleimides Heated at 300°C for 30 min...

Cross-Linking Reactions of Polymers. Bisdichloromaleimide-amine polymers contain (a) a double bond in the maleimidyl group, (b) chlorine, and (c) secondary amine group (-NH-). It may be possible to cross-link them either by the opening of the double bond (thermal polymerization) or by the nucleophilic displacement of chlorine by the secondary amine. The representative reaction scheme for such reactions is shown in Figure 6. The extent of such reactions may be evaluated by solubility measurements in dimethyIformamide. 

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