Effect of Chemical Structure on the Melting Temperature

For higher crystallization temperatures the polymer forms more perfect crystals that is, it is better annealed. Hence its melting temperature increases. 

The effect of structural irregularities can be illustrated by a study of polyesters (156) having the general structure 

The irregularity of the atactic propylene unit destroys crystallinity entirely. 

The effect of bond flexibility may also be examined utilizing the polyester structure (156). In this case substitutions in the rigid aromatic group are made  

Interchain forces can be illustrated by the following substitutions (156) of increasingly polar groups  

---