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PHASE SEPARATION IN THE MELT OF POLYPROPYLENE–1-DECENE COPOLYMERS

A propylene homopolymer and three copolymers with 1-decene containing 1.82, 3.55, and 7.83 mol% of comonomer units, respectively, were prepared with metallocene catalyst and the phase behavior in the melt of these polymers was studied using simultaneous synchrotron small-angle x-ray scattering and differential scanning calorimetry. The results show that the phase behavior of the melt varies with comonomer content and the copolymers tend to be phase-separated with increasing comonomer content. The phase separation in the melt of the propylene–1-decene copolymers was further confirmed by the fitting of the experimental data with Teubner–Strey micro-emulsion model and a transition from the phase-separated melt to the disordered melt was observed. We tentatively attribute this phenomenon to the inhomogeneous intra-molecular composition distribution at high levels of comonomer and the incompatibility of propylene sequences with different lengths. Such a finding is consistent with the facts of multiple melting peaks and mixed γ and α crystal phases in the polymer solids. Since the phase behavior depends on temperature, the effect of annealing temperature, from which the copolymers were cooled, on the nonisothermal crystallization of the copolymers was also investigated. It is found that higher degree of phase separation accelerates the crystallization but reduces the crystallization enthalpy.