Patent GB-1055304-A (GB)
Title: Process for forming polyurethane polymers from solution
Inventor: OERTEL HARALD
IPC: C08G18/10
Filed: 1963-09-04
Abstract: Highly elastic polyurethanes are prepared by reacting an -NCO terminated prepolymer (obtained by reacting a stoichiometric excess of aromatic diisocyanate with a substantially linear dihydroxy organic polymer of M.W. 600-5000 and of M.Pt. below 60 DEG C.) with an excess of a difunctional hydrazide or a substituted or unsubstituted hydrazine in an organic polar solvent, and reacting the product with a quantity of an organic polyisocyanate up to that equivalent to react with all of the excess hydrazide or hydrazine, the organic polyisocyanate being less reactive than aromatic diisocyanate and having -NCO groups which are less reactive than a sterically unhindered NCO group bonded to a benzene ring with only hydrogen atoms in the ortho positions.  The remaining hydrazine or hydrazide groups in the product may be reacted with an organic monoisocyanate, acid anhydride or pyrocarbonic acid ester to effect stabilization. The linear dihydroxy organic polymer may be a dihydroxy polyester, polyalkylene ether glycol, polythioether glycol, or dihydric polyacetal. The aromatic diisocyanate used in the first stage may contain two or more benzene nuclei which may be joined by O or S atoms and may be substituted, e.g. by chlorine atoms.  The polyisocyanate used in the final stage may be aliphatic, cycloaliphatic or mixed aromatic and aliphatic.  Aromatic polyisocyanates substituted in positions ortho to the -NCO groups may also be used.  The reaction between the dihydroxyl polymer and the diisocyanate may be carried out in the melt or in an inert solvent, e.g. CH2Cl2, CCl4, benzene, chlorobenzene, methyl ethyl ketone, tetrahydrofuran, dioxan, ethylene glycol monomethyl ether acetate or glycol formal.  The polar solvent for reaction of the propolymer with the hydride or hydrazine may be:  dimethylformamide, dimethylacetamide, dimethylsulphoxide, hexamethylphosphoramide, tetramethylene sulphone, N-methylpyrrolidone or tetramethyl urea which may be mixed with other solvents.  Many hydrazines and hydrazides are specified.  Carbodihydrazide is preferred. Stabilizing agents, e.g. phenyl b -naphthylamine, dinaphthyl - p - phenylenediamine, phenothiazine, mercapto - 2 - imidazoline, 3 - mercaptobenzimidazole, 2-(21 hydroxy - 51 - methyl benzene) benztriazole, 2 - methyl - 1,3 - diphenylimidazoline, 1,3 - diphenylhexahydropyrimidine, 1 - mercapto ethanol-2,1,10-dimercapto decane, thio-urea, o-aminothiophenol, triphenyl phosphite, diphenyl nonyl phosphite, or diphenyl phosphite, tartaric acid or crotonaldehyde 2,4-dinitrophenylhydrazone. Derivatives of benzophenone or diphenylmethane containing -OH groups may also be used.  In a typical Example (1) diphenyl methane 4,41-diisocyanate and dioxan were added to a copolyester derived from adipic acid, ethylene glycol and butane diol. The reaction mixture was heated for 100 minutes at 97 DEG  to 99 DEG  C. and then carbodihydrazide in dimethylformamide and TiO2 also in dimethylformamide were added. Finally, hexamethylene diisocyanate in dioxan was added and remaining free hydrazide groups removed by the addition of excess pyrocarbonic acid diethyl ester.