Self-nucleation effect in crystallization of Poly(propylene-co-ethylene-co-1-butene) terpolymers

Abstract

The self-nucleation effect on crystallization kinetics and polymorphism in poly(propylene-co-ethylene-co-1-butene) terpolymer was investigated using differential scanning calorimetry and wide-angle X-ray diffraction. The incorporation of ethylene and 1-butene comonomers induces the occurrence of self-nucleation, which hardly appears in customary isotactic polypropylene homopolymer. Within the incorporation range of 5.5–12.7 mol%, self-nucleation effect could increase the crystallization peak temperature by around 17 °C with respect to the relaxed melt. However, the temperature window of self-nucleation Domain II decreased with increasing comonomer content, where Domain IIa was absent at 12.7 mol%. The successive self-nucleation and annealing (SSA) analysis revealed that the three terpolymers studied exhibited similar regular sequence lengths but various distributions, where the diminishing of the self-nucleation effect was correlated to the reduction in long regular sequences. Additionally, the incorporation of ethylene and 1-butene comonomers facilitated formation of the triclinic γ form, which could be tuned by self-nucleation temperature T_s. In Domain I, the amount of γ form with respect to α form was kept constant. Interestingly, enhancing self-nucleation by lowering T_s significantly increased the content of γ form, as self-nucleation accelerated crystallization kinetics and increased the cooling crystallization temperature. However, the further reduction of T_s within Domain III favored the formation of α form by preserving crystallites from partial melting and reducing regular sequences for the subsequent crystallization.