ABSTRACT
When the effects are considered of chemical structures and phase structures of linear polyurethanes on their properties which are important from the viewpoint of materials technology, it is necessary to pay attention to thermal properties of those plastics. The previous chapter addressed the block structure of linear polyurethanes and its consequences for the phase transitions (recorded by DSC method) within glass transition temperatures of soft and hard segments, and for melting temperatures of crystalline structures formed within those phases. The effects of those parameters are also essential for thermal stability of PU plastics. What is especially important in this respect is the initial degradation temperature which is dependent on thermal stability of the weakest point(s) within the polyurethane macromolecule-urethane bonds and ester bonds. The initial decomposition point for the urethane bond (which is most representative for PUs) formed in the reaction of MDI and poly(ethyleneadipate) is 227°C [299]. Much higher decomposition temperature, i.e. 319°C, was recorded-in this case as the minimum in the DTG profi le-for poly(esterurethane) produced from TDI and polyesters derived from adipic acid, ethyl glycol and neopentyl glycol, and trimethylolpropane [300]. Decomposition of urethane bonds in PUs obtained from MDI, polyester of adipic and phthalic acids, and ethylene glycol, begins at 240°C, it reaches its maximum rate at 337-356°C, ester bonds which involve an aliphatic acid undergo destruction at 344°C, while those which involve an aromatic acid-at 386-400°C [276]. Decomposition of PUs obtained from TDI and castor oil or hydroxylated polybutadiene was observed to start as early as at 200°C and to run through three steps, with polybutadiene derived PUs being more stable [301].
