科研之友
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摘要
The ethylene-octene block copolymers in this study consist of long crystallizable sequences with low comonomer content alternating with rubbery amorphous blocks with high comonomer content. The crystallizable blocks form lamellae that organize into space-filling spherulites even when the fraction of crystallizable block is so low that the crystallinity is only 7%. These unusual spherulites are highly elastic and recover from strains as high as 300%. This new class of thermoplastic elastomers is fundamentally different from conventional elastomeric olefin copolymers that depend on isolated, fringed micellar-like crystals to provide the junctions for the elastomeric network. The elastomeric block copolymers are shown to be unique in that a hierarchical organization of space-filling lamellar spherulites provides the junctions for the elastomeric network. The deformation of the elastic spherulites is readily studied with small angle light scattering, wide angle X-ray diffractograms, and atomic force microscopy. At strains in excess of 300%, the spherulites break up into a fibrillar structure following lamellar deformation processes that are similar to those established for high density ethylenic polymers. The crystalline transformation produces a stiffer elastomer that exhibits complete recovery on subsequent loadings. Similar experiments on elastomeric random ethylene-octene copolymers where fringed micellar crystals provide the physical crosslinks that connect the rubbery, amorphous chain segments reveal significant differences.
- 出版日期2009-7-1
