**4. Conclusion**

As a result of this review compilation, it was concluded that the two main general factors that determine thermal resistance of PUs are its structure from one side and the presence of additives on the other side. The structural factors that influence thermal stability of PUs are the chemical nature and composition of hard (isocyanate plus chain extender) and soft (macrodiol) segments, its segregation, and PU thermoplasticity (derived from characteristic of TPU's stable linear structure). The additives that have a marked effect on augmenting thermal stability of PUs are mineral fillers (e.g., nano-oxides, nanoclays, talcs) and specific modifiers like POSS, flame retardants (both as additive and as polyol modifier), and fibers (natural or synthetic). Also, blending and grafting with other polymers are strategies that are utilized for increasing thermal resistance of PU, both for improving processing in manufacture and for high demanding applications. However, it is necessary to state that this review did not attempt to cover all particular factors that need to be taken into account when studying thermal stability of PU. Complex PU structures will

## *Thermosoftening Plastics*

potentially have several weak chemical links, variable intermolecular forces, different relevant properties such as thermal conductivities, and even environmental factors that may cause decomposition (i.e., hydrolysis by moisture, acidity, oxidative or non-oxidative atmosphere) will contribute to only predict thermal stability in more or less broad temperature ranges.
