PURPOSE: To obtain a material capable of forming a dense coating having a high hardness and resistances to heat, oxidation, wear, and chemicals by reacting a mixture of an inorganic dihalosilane and an organohalosilane with a Lewis base to obtain a complex mixture and reacting the resultant mixture with ammonia and water.

CONSTITUTION: A complex mixture obtained by reacting a mixture of an inorganic dihalosilane represented by formula I and an organohalosilane represented by formula II with a Lewis base is reacted with ammonia and water to obtain the objective copolymer. In the formulae, X is a halogen; R is an alkyl, alkenyl, cycloalkyl, aryl, alkylamino, or alkylsilyl; and n is 1 or 2. The copolymer comprises -SiH2NH-, RSiHNH-, SiH2O-, and -RSiHO as major repeating units and has a number-average mol.wt. of 100-100,000.