The pseudohexagonal γ′ phase of polyamide
1012 can
be obtained by melt-quenching and gradually transformed into the γ
form during heating, in which the trans methylene
segments away from the amide group are further twisted. What happens
during uniaxial stretching? In this work, the multistage structural
evolution of the γ′ phase during uniaxial stretching
has been studied by using in situ wide-angle X-ray scattering (WAXS)
and Fourier transform infrared spectroscopy (FTIR). The multistage
conformational evolution of the γ′ phase during stretching
was studied by quantitative analysis of the infrared progression bands
and was found to be closely correlated with the mechanical response
during tensile deformation. In the yield stage, the twisted methylene
segments in the initial γ′ phase undergo conformational
ordering under stress activation, and the γ′ phase spontaneously
transforms into a defective α phase. Furthermore, in the plateau
stage, strain induces significant conformational disorder and the
transient α phase transforms into the most conformationally
disordered γ phase. Finally, at the strain hardening stage,
the reversible crystal form transition from the γ phase to the
regular γ′ phase is induced by stress, accompanied by
an obvious conformational ordering process. The stress- and strain-induced
conformational torsional motions are found to be completely opposite,
with the former inducing conformational order and the latter inducing
conformational disorder.