Polyborosilazane and process for producing same

Claim 1

A polyborosilazane having a boron/silicon atomic ratio of 0.01 to 3 and a number-average molecular weight of about 200 to 500,000 and containing (a) skeletal groups of a recurring unit represented by the general formula: ##STR39## wherein R 1 , R 2 and R 3 , independently from each other, represent hydrogen, a hydrocarbyl group, a group other than the hydrocarbyl group and containing a carbon atom bonded to the silicon atom of the above general formula, an alkylsilyl group, an alkylamino group or an alkoxy group, with the proviso that at least one of R 1 , R 2 and R 3 is hydrogen and (b) at least one cross-linkage which cross-links said skeletal groups and which is selected from the group consisting of: ##STR40## wherein R 4 represents hydrogen, halogen, an alkyl group, an alkenyl group, a cycloalkyl group, an aryl group, an alkoxy group, an alkylamino group, a hydroxyl group or an amino group and R 7 represents a residue bound to the nitrogen atom of R 6 having a nitrogen atom, and wherein at least two of the six bonds of the group (iv) are used for the crosslinkage with the remaining bond or bonds, if any, being linked to hydrogen, halogen, an alkyl group, an alkenyl group, a cycloalkyl group, an aryl group, an alkoxy group, an alkylamino group, a hydroxyl group or an amino group.