Properties of ethylene–propylene copolymers and of terpolymers containing unsaturation

Abstract

AbstractThe elastomeric properties of amorphous ethylene–α‐olefin copolymers have been described in previous papers, as well as the importance of both the homogeneity of composition of each macromolecule forming the raw polymer and the statistical distribution of the two comonomers. It has been observed that a narrow distribution of the molecular weights is very important with regard to the mechanical properties of the cured synthetic rubbers obtained from the ethylene–propylene copolymers, whereas a not too high average molecular weight is important as far as the processability is concerned. One of the most interesting properties of the ethylene–propylene copolymers is their good aging resistance which is due to the saturated nature of the polymeric macromolecules. It has been observed that these properties are substantially shown also by those terpolymers consisting predominantly of ethylene and propylene (or other α‐olefins), and in addition a small amount of a monomer whose molecule contains more than one double bond; on polymerization these last monomers yield monomeric units still containing a double bond. A great number of monomers are well suited for the production of terpolymers with a low degree of unsaturation, which is sufficient for the conventional vulcanization methods adopted for other rubbers, particularly for those containing a low degree of unsaturation. It is quite essential, in order to obtain good vulcanizable products, that the unsaturation is regularly distributed in all the macromolecules, and that in each of these they are distributed at random. Probably, the differences observed with various monomers depend primarily on the ability of each monomer and of the copolymerization system adopted to meet to these requirements. This is the reason why we shall discuss the properties of those products in which a considerable homogeneity of distribution has been achieved. The mechanical and dynamic properties will be related to the degree of unsaturation. The results obtained from the use of such terpolymers for the production of elastomers have demonstrated that the elastic, dynamic, and aging properties remain essentially the same as those for the ethylene–propylene copolymers when the degree of unsaturation does not exceed 2–3%, expressed as number of double bonds per hundred monomeric units.