The new processes of anionic co-ordinated polymerization have permitted the synthesis of new polymers which are of interest as plastics, fibers, and elastomers. Among these last, the ethylene-propylene rubbers are particularly interesting for the future of the rubber industry. In fact these elastomers are prepared from low-cost raw materials (ethylene and propylene) and show good mechanical and elastic properties as well as excellent resistance to aging.
Our research directed to obtaining new rubbers based on the copolymerization of ethylene with propylene started some years ago. We soon succeeded in establishing that it was possible to prepare copolymers of these two monomers showing interesting elastomeric properties. From the beginning, the problem arose of how to vulcanize these copolymers: while certain interesting methods for direct vulcanization were investigated and identified, we also investigated the possibility of terpolymers containing unsaturation and therefore vulcanizable with the ingredients normally employed in the rubber industry, particularly for the low unsaturated rubbers. The problem involved some difficulties, due to the following three reasons. (1) In order to maintain the peculiar characteristics of resistance to aging and chemicals, typical of ethylene-propylene copolymers, it was necessary to obtain terpolymers in which the unsaturation was present in a very small amount. (2) To obtain valuable properties in the vulcanizates, the unsaturation had to be well distributed in all the macromolecules. (3) In order to avoid branching or crosslinks, the residual double bond of the diene entering the polymer chain must not be able to react further during polymerization. Our research led to a number of monomers which may copolymerize with ethylene and propylene and which, under suitable conditions, gave terpolymers having a sufficiently homogeneous composition. Investigation of the behavior, in anionic coordinated polymerization of hydrocarbons containing internal double bonds led to an interesting solution to the problem of producing terpolymers.
SynopsisSt.ress-temperature coefficients have been measured for a high-molecular-weight ethylene-propylene copolymer, containing 45 mole-% of ethylene, chlorinated and vulcanized with a cure system baaed on sulphur and accelerators. From the relationships:the thermodynamic functions [dE/bL] T
and -T [ d S / b L ] T have been determined in arange of the extension ratio up to (Y = 6.9. A good agreement has been found between the experimental data and the stress-strain theoretical curve obtained for a non-Gaussian type network.
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