Effects of different molecular architectures in terms of comonomer content and composition distribution on the miscibility of cyclic olefin copolymer/polyolefin (COC/POE and COC/LLDPEB) blends

In this work, morphology and rheology of the blends of cyclic olefin copolymer (COC) with two types of crystalline polyolefins were investigated through a wide range of compositions. The used polyolefins had various plasticity, elasticity and viscoelastic behavior. Their molecular structures were similar but their molecular architectures were different in terms of comonomer content and composition distribution (i.e., a linear low-density polyethylene with 4 mol% of 1-butene comonomer (LLDPEB labeled as LLB) and nonuniform composition distribution and a polyolefin elastomer (POE) with 33 mol% of 1-butene comonomer and uniform composition distribution). Morphology of the COC/POE blends was droplet-matrix at low concentrations of the dispersed phase which was changed to co-continuous morphology at intermediate concentrations. Good compatibility and adhesion between phases were also observed. In COC/LLB blends, droplet-matrix morphology and good compatibility were observed between the two phases, except for compositions of 70/30 and 50/50, which exhibited continuous morphology and phase separation. The results of morphology and rheological data such as Cole–Cole plots and variations of viscosity versus composition revealed that these blends were immiscible. The interfacial interaction of the blend phases was investigated using rheological diagrams of variations of their complex viscosities, storage modulus versus frequency, relaxation time spectra and tan d versus frequency. In addition, the interfacial tension was calculated using emulsion models. It was found that in the intermediate concentrations and COC-rich compounds, the interfacial interaction of the phases and form relaxation time of the dispersed particles of the COC/POE blends were higher than those of the COC/LLB blends, resulting in a further increase in elasticity. In blends with low COC content, the interfacial interaction of the phases and form relaxation time of the dispersed particles of the COC/LLB blends were higher than those of the COC/POE blends.