Abstract: Process for producing a high density elastic polyurethane of reduced weight having excellent resistance to bending, which employs as catalyst 4-methyl-1-(2-dimethylaminoethyl)piperazine or a mixture of 4-methyl-1-(2-dimethylaminoethyl)piperazine and another tertiary amine compound as co-catalyst.

Abstract: A silicon nitride powder having an enhanced sintering activity is prepared by heating a mixture of a nitrogen-containing silane compound and a sintering aid in a non-oxidizing atmosphere.

Abstract: A colored polymer emulsion having dispersed therein particles of a copolymer having at least 2.times.10.sup.-5 g-eq./g of the copolymer, of a phosphoric acid group or salt thereof. The copolymer particles have an average particle size of not larger than 1 .mu.m and a minimum film-forming temperature of not higher than 35.degree. C., and have been dyed with a basic dye. The emulsion is capable of forming a film having an improved water resistance and light resistance. The emulsion is prepared by polymerizing a monomer mixture comprising (a - 1) a monomer having a phosphoric acid group or a salt thereof, (a - 2) a hydrophobic monomer and (b) a optional hydrophilic monomer by an emulsion polymerization procedure, and then incorporating a basic dye to the obtained polymer emulsion, or by carrying out the emulsion polymerization in the presence of a basic dye.