Thermal degradation o f polyurethanes. Part VII. The effect of cross-linking density and type
of cross-linking bonds on the thermal stability of polyurethane elastomers
The course o f thermal degradation of four series of polyurethane elastomers differing in cross-linking density, type of cross-linking bonds (С—C and allophanate bonds) as well as type and molar ratio of chain extender (1,4-butanediol, triethylene glycol and polyethylene glycol) has been investigated. Polyurethanes have been prepared from diphenylmethane-4,4'-diisocyanate and polyesterdiols — poly(ethylene adipate) (PEA) and poly(ethylene maleate) as well as a copolyesterdiol with segments of oligo(ethylene terephthalate) incorporated into PEA chains. It has been found that during isothermal heating of polyurethanes at temperatures in the range of 533—573 К (260—300°C) degradation takes place in three stages differing in their rates. The degradation rate constants do not depend on the cross-linking density, type of cross-linking bonds and type of chain extender, but their numerical values increase withthe increase in molar ratio of chain extender.
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