Structural evolution of mesomorphic propylene–1‐butene random copolymer during heating process

Abstract

AbstractThe study of the transition of mesophase to α‐crystal (meso–α transition) is of great significance for understanding the crystallization, morphology as well as processability of polypropylene materials. The structural evolution of mesomorphic isotactic propylene–1‐butene (iPPBu) random copolymer during the continuous heating process was investigated using in situ Fourier transform infrared spectroscopy, differential scanning calorimetry, wide‐angle X‐ray diffraction and dynamic mechanical analysis. The presence of the butene comonomer influences the meso–α transition behavior. Compared with the mesomorphic iPP homopolymer, the presence of butene comonomer reduces both onset temperature (Tonset) and end temperature (Tend) of the meso–α transition, and narrows the transition temperature range. The content of the 31 helical sequence with 12 monomers remains invariant during the meso–α transition, differing from that of mesomorphic iPP homopolymer. Similar to mesomorphic iPP homopolymer, the 31 helical sequence with monomer number n ≤ 12 is found to exist in the rigid amorphous fraction of iPPBu, but is different from that of a mesomorphic propylene–ethylene random copolymer. In the meso–α transition (from 60 to 100 °C), the redshift of the peak position of the band at ca 841 cm−1 provides new information for the approaching of adjacent stems at the molecular level. Moreover, a new peak at around Tend is found in the tan(δ)–T plot, and is correlated with the meso–α transition. The activation energy of the meso–α transition of mesomorphic iPPBu is 32.5 kJ mol−1, which is slightly lower than that of mesomorphic iPP homopolymer. This work sheds new light on further understanding of the meso–α transition mechanism of iPPBu copolymer at the molecular level and elucidates the effect of butene comonomer on the meso–α transition. © 2021 Society of Industrial Chemistry.