In melt recrystallization of trans-1,4-polyisoprene (TPI), polymorphism was examined via differential scanning calorimetry (DSC), polarized optical microscopy (POM), and wide-angle X-ray diffraction (WAXD). Two crystal modifications of TPI, namely β-TPI (metastable form) and α-TPI (thermodynamic stable form), exhibit difference in their ability to hold the chain cluster in the melt, and β-TPI is considered to exhibit stronger melting memory effect when compared with that of the α-TPI. Irrespective of whether the chain cluster is from the α-TPI or β-TPI, the reduced energy barrier for nucleation leads to the formation of α-TPI. Furthermore, melt recrystallization of TPI benefiting from the contribution of chain clusters makes more chains packed in an orderly manner during recrystallization, and this ultimately leads to increases in crystallinity if the recrystallization occurs at low temperatures.
Read full abstract