Promotion of Self-Nucleation with Latent Form I Nuclei in Polybutene-1 and Its Copolymer

Abstract

The formation of Form I nuclei of polybutene-1 (PB-1) and its copolymer with polyethylene (PB1-ran-PE) has been studied by means of modified self-nucleation protocols. Even when the self-nucleation temperature was high enough and all Form II crystals melt, re-crystallization can be accelerated if the melt-crystallized sample was annealed at low temperatures (below 60 o C for PB-1 and 75 o C for PB1-ran-PE) for just 3 min. These results suggest the formation of latent Form I nuclei within Form II crystals. This hypothesis is consistent with the observed growth of a small amount of Form I crystals during heating, after previous annealing at temperature lower than 20 °C.In addition, a peculiar phenomenon was found in PB1-ran-PE, as both Form II and Form I′ can be induced by the presence of latent Form I nuclei, due to cross-nucleation and self-nucleation effects, respectively. The final ratio of the two kinds of crystal Forms is a result of the competition between the two nucleation rates, which strongly depend on crystallization temperature. In this work, we have shown that careful design of novel self-nucleation protocols can yield evidence of the early stages of Form II to Form I transition, even when the degree of transformed crystals is below the limit of detection of conventional techniques sensitive to crystalline order (DSC, WAXD, FTIR).

In situ POM and FTIR investigation on quiescent phase transition of polybutene‐1 from form II to form I

“…This means that form I hardly nucleates at such high annealing temperatures. This finding is consistent with previous report by Wang, where form I nuclei were found only below 60°C . This indicates that form I nucleation is temperature dependence.…”

“…In recent years, it was found that low‐temperature annealing benefited form I nucleation . Wang et al called these low‐temperature formed nuclei as latent nuclei, because conventional techniques, such as DSC, WAXD, POM, and FTIR, hardly detected them . They only can be inferred indirectly from subsequent nucleation effect.…”

“…After annealing at a lower temperature, form II could transform to form I at a high temperature more rapidly. Annealing at the lower temperature was believed to promote form I nucleation, while annealing at the high temperature facilitated crystal growth . The nucleation at the lower temperature was also attributed to intercrystalline links .…”

“…A majority of past works were based on wide‐angle X‐ray diffraction (WAXD) and differential scanning calorimetry (DSC), because they can discriminate form I from form II easily. Nevertheless, the information obtained from these tools is normally trivial.…”

Enhanced beta to alpha recrystallization in beta isotactic polypropylene with different thermal histories

“…Incidentally this can be considered a case of hetero‐polymorphic self‐nucleation, similar to the case of the enhanced form II crystallization kinetics produced by self‐nuclei obtained from the melting of trigonal form I crystals in poly(1‐butene) . The recrystallization of the α‐phase from β‐phase self‐nuclei is favored by the larger growth rate of the former polymorph above 140°C, and possibly by the extensive occurrence the of α‐on‐β cross‐nucleation, which presents an overwhelming rate at these temperatures …”