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The influence of strain rate on the deformation induced crystal transition from forms II to I of Polybutene-1 is investigated by in situ Wide Angle X-ray Diffraction at different temperatures. The structural evolution during the subsequent stress relaxation is further monitored. As strain rate increases, the phase transition rate decreases apparently, while the dependence on stress and strain also becomes weak. The phase transition during deformation with three strain rates shows consistent dependence on external work. The transition rate in terms of form I content drops instantly when stretching stops. Further analysis on the evolution of crystallinity and orientations of both forms II and I shows that a small amount of recrystallization occurs in form II during stress relaxation at 80 °C, accompanied by a continuous increase in the content of form I, which further confirms occurrence of deformation induced melting and recrystallization. Structural evolution of Polybutene-1 during the deformation induced phase transition from forms II to I and the following stress relaxation process is investigated by in situ Synchrotron Radiation Wide Angle X-ray Diffraction (SR-WAXD). During the tensile with different strain rate, the phase transition rates show consistent dependence on external work. After deformation at 80 oC, crystallinity of unstable form II increase inversely, while the phase transition from forms II to I continues at a slower rate. The full cycle consideration provides a more comprehensive basis for the use of materials. [Display omitted] • The structural evolution of Polybutene-1 during stress relaxation is first considered. • The phase transition rates during deformation with three strain rates show consistent dependence on external work. • Recrystallization of unstable form II is found during stress relaxation after deformation at high temperature. [ABSTRACT FROM AUTHOR]

Abstract: With three polymers (poly(1-butene), isotactic polypropylene and syndiotactic polypropylene) as model systems, the effect of extensional strain on the nucleation rate was studied using a home-made miniature extensional rheometer and in-situ X-ray scattering. A non-monotonic correlation between nucleation rate and strain is observed around rheological yield point. Increasing strain leads to an increase in nucleation rate as expected when strain is smaller than yield strain, however, it results in a decrease in nucleation rate when strain slightly exceeds yield. We proposed that disentanglement occurs at yield point and thus decelerates flow-induced nucleation. Disentanglement provides freedom for chains to retract and leads to a dissipation of the energy initially imposed by extensional flow, which consequently weakens the effect of flow field on the enhancement of nucleation. [Copyright &y& Elsevier]