Molecular structure diene rubbers

Unconjugated dienes can produce an even more complicated range of macro-molecular structures. Homopolymers of such monomers are not of current commercial importance but small proportions of monomers like 1,5-cyclooctadicne are copolymerized with ethylene and propylene to produce so-called EPDM rubbers. Only one of the diene double bonds is enchained when this terpolymeriza-tion is carried out with Ziegler-Natta catalysts (Section 9.5). The resulting small amount of unsaturation permits the use of sulfur vulcanization, as described in Section 1.3.3. 

BIMS-NR blends as sidewall components. In many of the applications, the saturated elastomer is considered a polymeric antioxidant for the diene rubber. It is believed that the higher molecular weight polyolefins are better in these applications due to limited interdiffusion and a more stable morphology. Some of the benefits in tensile properties and abrasion resistance of the blends may be due to the interdiffusion of high molecular chains of dissimilar elastomers across the phase interface. Significant advances have been made in modifying the structure of polyolefin elastomers to increase the compatibility to unsaturated elastomers. Tse et al. [50b] have shown that uncompatibilized blends of saturated elastomers and unsaturated elastomers are possible if the former contains substantial amounts (>12%) styrene residues. This is expected to be an important area of development in the future with the advent of new synthesis procedures for polyolefins. 

This section studies the effect of the structure and composition of carbon nanofibers obtained by co-catalyst washed and not washed from the metal catalyst on the kinetics and properties of vulcanized ethylene propylene diene rubber. It is shown that the fibers obtained on the co-catalyst accelerate the crosslinking of EPDM, improve the physical and mechanical properties, increase the molecular mobility. The purpose of this research—investigation of the carbon nanofibers influence produced by co-catalysts on the physical and mechanical properties and structure of synthetic EPDM. 

The amount of information that may be gained from a study of the rubber network is thus rather limited in terms of detailed molecular structure. Whilst some idea of the relative frequency of C—C, monosulphidic, disulphidic and polysulphidic cross-links may be obtained, little can be inferred concerning the point of attachment of the cross-link, of pendent sulphur-containing moieties, of conjugated diene fragments or possible chain scission processes. 

A new method based on thermomechanical analysis of solid (not dissolved) polymer was used to study the topology and molecular structure of different kinds of sulphur (mineral and two polymeric types), commonly used as vulcanising agents for diene rubbers. It was found that a significant difference existed in their MWDs and in their degrees of crystallinity. Both mineral and polymeric sulphurs had a polymeric nature. 9 refs. EASTERN EUROPE POLAND RUSSIA Accession no. 645667... 

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