Crystallization Behavior of Modified Polyester with Varied Macromolecular Architecture

Several modified polyesters with varied macromolecular architecture, such as branched poly(ethylene terephthalate) (PET) based on glycerol (GL) from 0.004 to 0.05 mol ratio as a branching agent, blocked and branched poly(butylene terephthalate)‐polyether containing poly(tetramethylene oxide) (PTMO) as soft segment and GL as a branching unit, as well as segmented poly(ethylene terephthalate)‐polyether,were prepared. Their crystallization behavior was studied by differential scanning calorimetry (DSC), wide‐angle X‐ray diffraction (WAXD), and polarized optical microscopy (POM). It was found that a small extent of branching may enhance the crystallization of poly(ethylene terephthalate), while high degrees of branching (0.035–0.05) could block the development of crystallization. On the other hand, for even a small extent of incorporation of GL in the more flexible poly(butylene terephthalate)‐polyether chains, no enhanced crystallization was observed; blocking of crystallization from a branching defect may play the main role. The introduction of PTMO in poly(ethylene terephthalate) chains to a small degree facilitated the nucleation and speeded crystallization, but decreased the melting points of the polymers. A small number of nuclei and the greater induction time were found for branched PETs. The spherulities developed in branched PETs were larger and more perfect than those in PET due to less truncation of spherulites resulting from fewer nuclei, whereas the size of spherulities in poly(ethylene terephthalate)‐polyether became smaller with the increase of PTMO.