Patent GB-1353413-A (GB)
Title: Shaped articles of crosslinked polyurethane resins and process  for the production thereof
IPC: C08G18/79
Filed: 1971-08-11
Abstract: 1353413 Polyurethane films and filaments BAYER AG 11 Aug 1971 [10 Sept 1970] 37626/71 Heading B5B [Also in Divisions B2 and C3] In a process for the production of cross-linked shaped polyurethane products, high molecular weight uretdione polyurethanes which are free from NCO groups are shaped and cross-linked with reactive components selected from the groups of (a) polyamines, which contain primary or secondary amino groups attached to aliphatic carbon atoms and/or (b) polyfunctional compounds, optionally of molecular weight below a thousand, which have at least one primary or secondary amino group attached to an aliphatic carbon atom and at least one other group containing a reactive hydrogen atom attached to nitrogen, selected from the series of hydrazide group, semi-carbazide group and carbazic acid ester group and/or aromatically linked amino group, and/or (c) dihydrazide compounds having hydrazide, semi-carbazide and/or carbazic acid ester end groups, and/or (d) hydrazine, which are caused to act on the shaped polyurethane products which contain uretdione groups either during or after the shaping process to bring about cross-linking. The polyamines may have molecular weights of below 1000 and preferably below 500. Thus preferred polyamines are diprimary aliphatic C 2  to C 12  alkylene diamines, cycloaliphatic diamines of the cyclohexane or dicyclohexyl methane series and diamines of the xylylene series. Preferably, such di-primary diamines comprise a major proportion of ethylene diamine and/or para- or meta-xylylene diamine. Poly-functional reactive components suitably have a functionality of not more than 3. The reactive components are preferably employed at temperatures of below 80‹ C., suitably at about room temperature. Solutions of the reactive components in organic solvents, aqueous solvent mixtures or water may be used, suitably in concentrations of 0À001 to 50À0% by weight of the reactive components, especially 0À01 to 10% by weight. Desirably, the uretdionecontaining polyurethanes contain at least 0À05 equivalents of uretdione groups per kilogram of solid polyurethane substance and have an intrinsic viscosity, determined at 20‹ C. in hexamethyl phosphoramide, of at least 0À35. Polyurethanes which are stable in storage and which still contain uretdione groups which have not yet been cross-linked may be dissolved in polar solvents such as tetrahydrofurane or better in highly polar solvents such as dimethyl formamide or dimethyl sulphoxide. It is preferred however, to synthesize the polyurethanes which contain uretdione groups directly in polar solvents, polyurethane solutions which contain uretdione groups being thus obtained directly. Solutions of high molecular weight polyurethanes which are free from NCO groups and which have a uretdione content of at least 0À05 equivalents per kilogram of polyurethane may be spun into baths of the liquid reactive components or their solutions so as to produce highly elastic crosslinked polyurethane filaments or films. Films or coatings, which may be made micro-porous, may be obtained by painting a solution of a high molecular weight polyurethane which contains uretdione groups and which is free from NCO groups in thin layers on a support and then coagulating the layer in a bath of a non-solvent for the polyurethane, optionally after a preliminary treatment in a moist atmosphere, and the reactive components are caused to act on the polyurethane solution during or after coagulation to bring about cross-linking. Preparations of uretdione polyurethanes are given in Example 1, which also describes a wet spinning method in which the polyurethane is wet spun into a precipitation or cross-linking bath containing water or mixtures of solvents and water, e.g. dimethyl formamide/water 10 : 90 with varying proportions of reactive cross-linking components, the filaments being thereafter washed and sometimes treated again with a reactive component in a third bath. The filaments may be again treated with water at an elevated temperature before drying. Specified cross-linking agents are ethylene diamine, cyclohexane-1,4-diamine, para-xylylene diamine, N-methyl-bis-(γ-aminopropyl) - amine, bis - (γ - aminopropyl) - N,N<SP>1</SP>- piperazine, 2,5-dimethylpiperazine, piperazine hexahydrate, diethylene triamine, or triethylene tetramine. Various after-treatments are described. Further preparations of polyurethanes are given in Examples 2 to 19. The preparation of filaments is further exemplified in Examples 2 to 9, 11 to 16, and 18 and 19. The preparation of films is illustrated in Examples 3, 8, 17 and 18, and the preparation of-micro-porous films is described in Examples 8, 17 and 18. Example 3 describes the production of transparent films which are not cross-linked by pouring the uretdione polyurethane solution on to plates and then evaporating off the solvent at 100‹ C. If the films are treated in dilute methylolic solutions of meta-xylylene diamine, cross-linked films are obtained which are insoluble in dimethyl formamide and have improved elastic properties. Cross-linking may also be obtained by using di-hydrazides or by exposing the uretdione polyurethane films to a diamine atmosphere, e.g. ethylene diamine vapour at 25‹ C. for 10 minutes. Example 8 is similar to Example 3. Cross-linked films are obtained by causing ethylene diamine vapours to act on a moist film. Non-porous films soluble in dimethyl formamide are also cross-linked by aftertreatment in methanol containing 1% metaxylylene diamine at 60‹ C. for 5 minutes. In Example 17 transparent films soluble in dimethyl formamide and practically impermeable to water vapour are made by applying a polyurethane solution to plates and evaporating the solvent at 100‹ C. under a slight vacuum. If the freshly cast film is coagulated in water however, a micro-porous film is obtained which is also soluble in dimethyl formamide. Such film is rendered insoluble in this solvent by aftertreatment with methanol containing metaxylylene diamine. The film may also be crosslinked for a short time by means of other specified diamines. In Example 18, films are made by casting, which are subsequently rendered insoluble in dimethyl formamide by treatment with ethylene diamine, or carbodihydrazide. If the elastomer solution is painted on a glass plate to form a layer which is then exposed to steam and then placed in an aqueous coagulation bath containing ethylene diamine and dried, a microporous film permeable to water vapour is obtained, which only dissolves in dimethyl formamide at elevated temperatures.