Observations are reported in isothermal torsional oscillation tests on melts of isotactic polypropylene (iPP) and low-density polyethylene (LDPE) in the intervals of temperature between 190 and 250 C (iPP) and between 120 and 190 C (LDPE). With reference to the concept of transient networks, constitutive equations are developed for the viscoelastic response of polymer melts at three-dimensional...

In this work, poly(lactic acid) (PLA) dimer model compounds with different tacticities were synthesized and studied in detail by 1H and 13C nuclear magnetic resonance (NMR) in three solvents, deuterated chloroform (CDCl3)/CCl4 (20/80 v/v), CDCl3 and dimethyl sulfoxide -d6. All of the peaks in the 1H and 13C NMR spectra were assigned with the help of two-dimensional NMR. Although the solvents we...

Spatio-temporal growth of isotactic polystyrene single crystals during isothermal crystallization has been investigated theoretically based on the phase field model by solving temporal evolution of a nonconserved phase order parameter coupled with a heat conduction equation. In the description of the total free energy, an asymmetric double-well local free energy density has been adopted to repr...

In this study, the crystallization behavior of oriented isotactic polypropylene during solid-state stretching was investigated by in-situ wide-angle X-ray scattering. Results showed that a new arc appeared on (040) reflection with previous arcs remained when direction inclined to initial orientation direction, as result induced crystallization. The process occurred later than yielding but earli...