Macromolecules, 2018, vol 51, 6, pp. 2232-2239
The retardation of polybutene-1 form II to form I transition in the late stage has been investigated by means of time-resolved wide-angle X-ray diffraction. Form II samples with different lamellar thickness and constituent in amorphous phase were generated via varying crystallization temperature and molecular weight and aged at room temperature for the form II to form I transition. The II to I polymorphic transition in polybutene-1 undergoes two stages, where slow nucleation and rapid growth proceed in the first stage and extremely slow secondary nucleation and growth take place in the late stage. The degree of transition reaches a plateau value in the late stage of transition, which depends highly on crystallization temperature and molecular weight that low molecular weight and high crystallization temperature always contribute to a greater degree of transition, but is less affected by the kinetics in the first stage. According to the crystal unit cell parameters of form II and form I, there should be an extension in the normal direction of lamellae and a shrinkage in the lateral direction during phase transition, which thus would induce an additional pressure in the normal direction and the tendency to expansion in the lateral direction on the residual from II crystallites. As a result, the nucleation and further growth of the II to I transition are retarded. Low molecular weight and high crystallization temperature lead to larger content of chain ends and higher chain mobility in the amorphous phase; hence, the samples are more likely to release the unfavorable factors restraining generation of form I nuclei to some extent. The transition degree in late stage is thus an intrinsic property of PB-1 samples determined by their microstructures and would not be influenced by the transition behavior in the first stage.