The thermoplastic properties of the most important classes of polymers like polyolefins, polyesters, polyamides and poly-urethanes arise from the fact that they are able to crystallize from the melt into semi-crystalline solids. The extent to which linear macromelecules can be incorporated into a crystalline morphology depends on several factors. The crystallisation conditions, namely temperature, cooling rate, rheological situation are all important. Further, perfection of the macro-molecular structure, e.g. presence or absence of comonomer units, defects in the stereo regularity as in polymers showing tacticity (polypropylene is an example) play an important role in defining what can be reached as optimal degree of crystallization.
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