Effect of the blend ratio of cyclic and linear polyethylene blends on isothermal crystallization in the quiescent state

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The role of entanglements that form between cyclic and linear polymers in crystallization is of particular interest, but it is not fully understood. We investigated the crystallization behaviors of blends of cyclic polyethylene (C-PE) and linear polyethylene (L-PE) in a quiescent state to elucidate the role of this novel entanglement in crystallization. The samples were prepared by mixing the prepared C-PE and L-PE specimens at L-PE weight fraction (ΦL-PE) values of 0–100 wt%, with the weight average molecular weights of C-PE and L-PE being 175 × 103 and 154 × 103, respectively. The isothermal crystallization behaviors were analyzed through polarizing optical microscopy (POM) and differential scanning calorimetry (DSC). The morphology observed through POM was similar to that of ΦL-PE. From the time evolution of the heat flow measured via DSC, we obtained the half-crystallization time (t1/2) values as functions of ΦL-PE at different degrees of supercooling (ΔT). The 1/t1/2 values of the C-PE and L-PE homopolymers were approximately the same at ΔT = 25.5 and 26.5 K. At a larger ΔT value, the 1/t1/2 value of C-PE was significantly larger than that of L-PE. In contrast, 1/t1/2 reached a minimum value at ΦL-PE = 30–40 wt%, irrespective of ΔT. As the entanglement density increased with increasing ΦL-PE, the crystallization rate was expected to decrease monotonically. By considering the experimental relationship between 1/t1/2 and ΦL-PE, we speculated that the suppression of crystallization in the blended system was caused by a novel entanglement formed by the penetration of the L-PE chain into the C-PE chain.