Abstract: A membrane filter material formed from a solvent resistant bimaleimide polymer which is formed by polymerizing a bismaleimide compound with a perhydrodiaza-type heterocyclic compound and has a main structural skeleton represented by the following formula: ##STR1## wherein R.sub.1, R.sub.2, R.sub.3 and R.sub.4 represents a lower carbon chain which is linear or contains a methyl group or ethyl group on the side chain, R.sub.5 represents a divalent group containing an aromatic ring, Y is >R< or >N--R--N< in which R is a lower carbon chain, and m is 0 or 1.This bismaleimide polymer can be a membrane filter material having an excellent organic solvent resistance. When this polymer is formed into a hollow fiber or plain film, a high separating and filtering capacity and an excellent organic resistance can be attained.

Abstract: A membrane filter material formed from a solvent resistant bismaleimide polymer which is formed by polymerizing a bismaleimide compound with a perhydrodiaza-type heterocyclic compound and has a main structural skeleton represented by the following formula: ##STR1## wherein R.sub.1, R.sub.2, R.sub.3 and R.sub.4 represents a lower carbon chain which is linear or contains a methyl group or ethyl group on the side chain, R.sub.5 represents a divalent group containing an aromatic ring, Y is >R< or >N--R--N< in which R is a lower carbon chain, and m is 0 or 1.This bismaleimide polymer can be a membrane filter material having an excellent organic solvent resistance. When this polymer is formed into a hollow fiber or plain film, a high separating and filtering capacity and an excellent organic resistance can be attained.

Abstract: An electret article comprising an even number of electret plastics films laminated together, with the surfaces of the same polarity facing each other, said laminate having the same polarity on both external sides. It keeps its high surface charge density. It will find use in such applications as acoustic materials, filters, and medical supplies.