Patent GB-914609-A (GB)
Title: Polyurethane plastics
IPC: C08G18/10
Filed: 1961-02-23
Abstract: A process for the preparation of cross-linked polyurethane plastics comprises reacting a monomeric polyisocyanate with an acid hydrazide having a molecular weight of at least 400, or reacting a prepolymer containing free, isocyanate groups (said prepolymer having a molecular weight of at least 400 and being obtained from a monomeric polyisocyanate and a polyhydric alcohol, polyhydric phenol, hydroxyl group-containing polyester, polyhydric polyalkylene ether, polyhydric polythioether or polyacetal) with an acid hydrazide which may or may not have a molecular weight of at least 400, the amount of monomeric polyisocyanate or prepolymer used being such that there is more than one NCO group present for each hydrazide group.  The process at an intermediate stage gives materials characterized by the presence of the grouping <FORM:0914609/IV(a)/1> in which R is a hydrogen atom or an alkyl radical; R1 and R11 are carbon atoms of an aliphatic; cycloaliphatic or aromatic bond.  Excess NCO groups react with the hydrogen atoms of this grouping.  Aliphatic, hydroaromatic and aromatic polyisocyanates are listed.  Mixtures of polyisocyanates and monoisocyanates (which may contain chlorine, cyanogen, ester or alkoxy substituents) can also be used.  Reactants for the preparation of the prepolymers are also listed.  The hydrazides can be prepared from hydrazine or derivatives such as methylhydrazine and mono- or polycarboxylic acids (which may be substituted) including those obtained by saponifying alcohol addition products of acrylonitrile or those obtained by hydrogenation of acids produced by the diene synthesis. Sulphur-containing carboxylic acids are also referred to. Hydrazides of sulphonic acids, carbodihydrazide and thiocarbohydrazide are also mentioned.  The carboxylic acid hydrazides having a molecular weight greater than 400 can be prepared by reacting an appropriate polycarboxylic acid (e.g. polymers and copolymers of acrylic or methacrylic acid or styrenemaleic acid copolymers) with an alkyl pyrocarbonate and then reacting with hydrazine.  Dimerization products of fatty acids and polyethers containing terminal carboxyl groups, e.g. those obtained by the process of Specification 634,496 are other suitable starting materials for the hydrazides. Isocyanate-modified prepolymers, such as the one obtained by reacting a linear hydroxy-polyester of molecular weight 2000 with hexamethylene diisocyanate at an NCO to OH ratio of about 2 can be reacted with a monocarboxylic acid hydrazide to give a pasty reaction product which can be processed in a kneader. If all the isocyanate is added at once there should preferably be provided 3 to 4 NCO groups for each hydrazide group.  In a two step process one equivalent of NCO is used in the first step and 2 to 3 equivalents in the second step.  Reaction can be carried out in solution in ethyl acetate, dimethyl ether, formamide, dimethylformamide, methylene chloride, dioxan, tetrahydrofuran or 1,3-dioxolane.  Tertiary amines and tin compounds are suitable catalysts.  In examples (1) a prepolymer from the reaction of an adipic acid-diethylene glycol polyester, octadecane-1,12-diol and trimethylol propane is reacted with acethydrazide in ethyl acetate and the product is mixed with a trimethylol propanetoluene diisocyanate reaction product and used to form a film; (2) a hydrazide of dimerized linseed oil fatty acid is mixed with ethyl isocyanate and a prepolymer obtained as in Example 1 and a solution of the mixture is baked as a film; (3) a prepolymer from a branched polypropylene glycol ether and hexamethylene diisocyanate is kneaded with propionic acid hydrazide in dimethyl formamide and the paste obtained is heated with a polyisocyanate and the mixture is then moulded; (4) thiodipropionic acid bis-hydrazide is used in a process generally similar to that of Example (1).  Specifications 798,209, 840,097, 842,420 and 876,503 also are referred to.