Reexamining the role of intercrystalline links in the II-I phase transition of Poly(1-butene)

Abstract

Despite being studied extensively, the role of intercrystalline links has not been elucidated completely. To clarify its role, two kinds of different lengths of poly (1-butene) chains were blended with different proportions, among which only the long chain was able to form intercrystalline links. Phase transitions of these blends were monitored with time-resolved FTIR. Surprisingly, when the content of long chains reached 30% or 40%, phase transition rates were even slower than they existed alone, indicating phase transition was suppressed greatly by long chains. Adding a minority of short chains actually would also slow down the phase transition, though the effect was not as obvious as long chains. Estimation indicates that the change of enthalpy cannot compensate for the loss in conformational entropy in II-I phase transition. To ensure continuous proceeding of II-I phase transition, the role of amorphous chains is indispensable in the quiescent phase transition. Nevertheless, the role of intercrystalline links should not be undue stressed either. Analysis indicates that a transient amorphous network exists in the blends, consisting of different sizes of amorphous coils. Long chains can form larger coils because of intercrystalline links, while small coils are most likely from individual short chains. Entanglements exist between these amorphous coils, stabilizing the transient network, which would also affect phase transition significantly. When a minority of short chains are added, stress on one side of some big coils reduces. The big coils deviate from previous mass centers, slowing down its internal stress on form II crystal and thus its phase transition rate. Conversely, when a minority of long chains are added, big coils not only would lead small coils deviating from their previous mass centers, but also slow down contraction of the small coils through the entanglement, leading to a larger decrease in form I nuclei. The roles of intercrystalline links and entanglement should be considered simultaneously.