Isoprene rubber is a synthetic rubber . Elastic dark gray mass without a characteristic odor. The chemical composition of isoprene is approximately identical to natural rubber, so the properties of these two elastomers are similar.
Synthetic isoprene rubbers combine well with all diene rubbers. The most important property of dienes is their ability to polymerize, which is used to produce synthetic rubbers.
Obtained by catalytic stereospecific polymerization of isoprene in solvents :
n CH 2 = C (CH 3 ) -CH = CH 2 → (-CH 2 -C (CH 3 ) = CH-CH 2 -) n
This synthetic rubber is mainly trans -1,4-polyisoprene. Polymerization of isoprene by the action of initiators such as sodium or potassium in low-polar solvents results in the formation of 1,2-, 3,4- and trans-1,4-polyisoprene. The initiation of lithium polymerization in a non-polar solvent leads to the production of rubber containing 94% cis units. The use of Ziegler-Natta catalysts makes it possible to obtain rubber that is almost identical to natural. In the polymerization of isoprene in the absence of stereochemical control, in principle, the formation of various polymer products is possible.
Content
History
Natural rubber is isoprene rubber. Therefore, the scientists were faced with the task of obtaining synthetic isoprene rubber. The synthesis of such rubber was carried out. But the properties of natural rubber were not fully achieved. The reason for this was established when the spatial structure of natural rubber was studied. It turned out that it has a stereoregular structure, —CH 3 groups in the rubber macromolecules are not randomly located, but on the same side of the double bond in each link, that is, they are in the cis position.
Properties
- working temperature range: from −55 ° C to +80 ° C; low glass transition temperature (about −70ºС);
- crystallization upon stretching or upon cooling: the half-cycle of crystallization of unstretched rubber SKI-3 - more than 20 hours.The ability of SKI to crystallize upon stretching and the flexibility of its macromolecules determine the high elasticity and strength of unfilled and filled rubbers based on it, as well as good dynamic properties. The smallest relative elongation at which the formation of a crystalline phase is observed at 20 ° C is 300–400% for rubbers based on it;
- excellent rebound elasticity;
- very good tear and abrasion strength, tensile strength;
- good electrical insulation resistance ;
- solubility = 16.8 (MJ / m³); good water resistance.
- Rubbers are produced with a given viscosity. During processing, it is necessary to strictly observe the temperature regimes of mixing, heating and molding.
Weaknesses
Poor resistance to heat, ozone and sunlight.
Very low resistance to oils , gasolines and carbon solvents.
The main drawback of SRS related to the molecular structure and MMP features is the reduced cohesive strength of rubber compounds based on them (reduced crystallization rate of synthetic polyisoprene, lack of functional polar groups in macromolecules). When assembling informal, glued and other products, there are difficulties associated with the increased stickiness of mixtures and semi-finished products, insufficient frame, fluidity during transportation and storage.
Application
The use of complex catalysts based on derivatives of titanium and aluminum makes it possible to obtain rubbers of the SKI-3 type with a high content of cis-1,4 units attached almost exclusively to the head-to-tail type. SKI-3 has a regular structure, contains no rubber components, and there are no functional groups in the polymer molecular chains. Rubber has a narrow molecular weight distribution.
Due to the high unsaturation, SKI-3 vulcanization can be carried out using vulcanizing systems containing sulfur and organic vulcanization accelerators, as well as sulfurless systems: thiuram , organic peroxides, phenol-formaldehyde resins , maleimide derivatives and other substances. Sulfur vulcanizing systems are mainly used in industry. Typically, the vulcanization temperature of sulfur mixtures based on SKI-3 is 133–151 ° C. They are characterized by the presence of an optimum vulcanization in terms of tensile strength and a small plateau of vulcanization.
Since SCI is prone to crystallization, vulcanizates based on it, even not filled, have high strength up to 30 MPa. At elevated temperatures, tear resistance and strength decrease. Due to the absence of nitrogen-containing substances and low ash content, SKI are characterized by good water resistance and high dielectric properties.
References and Sources
- Typische Eigenschaften von Isoprenkautschuk (link unavailable) ( German )
- Anwendung von Isoprenkautschuk bei der Rohrisolierung ( German )
- Goncharov A. І., Sereda І.P. Chemical technology . Part 2. - Kiev: Vishka school., 1980 p. - 280s. ( Ukrainian )