Structure Formation and Crystallization Behavior of Ethylene-Isoprene Block Copolymers and Their Blends with Corresponding Homopolymers
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Time-resolved simultaneous synchrotron small-angle X-ray scattering and differential scanning calorimetry experiments have been performed on crystallization of polyethylene-polyisoprene diblock copolymers (HEI or LEI) and their blends with corresponding homopolymers, polyethylene (PE) and polyisoprene (PIp). For the neat block copolymer having a 50 wt% of the crystalline component, preexisting microphase separation structure in the melt was kept at high and low crystallization temperatures <i>T</i><sub>c</sub> (<i>T</i><sub>c</sub>≥94°C and <i>T</i><sub>c</sub><60°C), while disrupted at intermediate <i>T</i><sub>c</sub> (60°C≤<i>T</i><sub>c</sub><94°C). This complex behavior was interpreted by combination of two mechanisms. The behavior in the crystallization below 94°C was attributed to the competition between the crystallization and chain diffusion rates, that is, the fast crystallization rate at lower <i>T</i><sub>c</sub> makes it difficult to rearrange the phase structure in the melt. On the other hand, at a higher <i>T</i><sub>c</sub> (≥94°C), the preservation of the microphase separation structure was explained by a small degree of crystallinity due to the ethyl branch of polyethylene (hydrogenated poly(butadiene)). For HEI/PE blends, crystallization behavior was the simple superposition of those for HEI and PE, while, for HEI/PIp with a small composition of PE, suppression of crystallinity was observed. Crystallization kinetics in the neat block copolymer and all the blends was not so different from that in the PE homopolymer.
- e-Journal of Soft Materials
e-Journal of Soft Materials (4), 12-22, 2008
THE SOCIETY OF RUBBER SCIENCE AND TECHNOLOGY, JAPAN