New challenges and opportunities for polyolefin blends arise from the recent introduction of olefin block copolymers (OBCs). In this study, the effect of chain blockiness on the miscibility and phase behavior of ethylene-octene (EO) copolymer blends was studied. Binary blends of two statistical copolymers (EO/EO blends) that differed in comonomer content were compared with blends of an EO with a blocky EO copolymer (EO/OBC blends). The blends were rapidly quenched to retain the phase morphology in the melt and the phase volumes were obtained by atomic force microscopy (AFM). Two EOs of molecular weight about 100 kg/mol were miscible if the difference in octene content was less than about 10 mol % and immiscible if the octene content difference was greater than about 13 mol %. The blocky nature of the OBCs reduced the miscibility and broadened the partial miscibility window of the EO/OBC blends compared with the EO/EO blends. The EO/OBC blends were miscible if the octene content difference was less than 7 mol % and immiscible above 13 mol % octene content difference. It was also found that the phase behavior of EO/OBC blends strongly depended on blend composition even for constituent polymers of about the same molecular weight. Significantly more demixing was observed in an OBC-rich blend (EO/OBC 30/70 v/v) than in an OBC-poor blend (EO/OBC 70/30 v/v). An interpretation based on extractable fractions of the OBC described the major features of the EO/OBC (30/70 v/v) blends. V V C 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys

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Miscibility of homogeneous propylene/ethylene (P/E) copolymers of relatively narrow molecular weight distribution was studied as a function of constituent comonomer content. Polymers with up to 31 mol % ethylene were blended in pairs in order to vary the comonomer content difference. Binary blends were rapidly quenched from the melt to retain the phase morphology, and the phase volume fractions were obtained from AFM images. Copolymers of molecular weight about 200 kg mol-1 were miscible if the difference in ethylene content was less than about 18 mol % and immiscible if the ethylene content difference was greater than about 20 mol %. Blends with constituent composition difference in the range of 18−20 mol % exhibited partial miscibility in the melt as indicated by a phase volume fraction that was different from the blend volume fraction. The temperature dependence of blend morphology confirmed the UCST behavior of P/E copolymer blends. The phase composition and the χ interaction parameter were extracted by using an approach that considered the molecular weight distribution. The compositional dependence of χ conformed to the copolymer equation and depended on comonomer content difference only, not on comonomer content per se.

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