Cis-1,4 polyisoprene

Natural rubber, cis-1,4-polyisoprene, cross-linked with sulfur. This reaction was discovered by Goodyear in 1839, making it both historically and commercially the most important process of this type. This reaction in particular and crosslinking in general are also called vulcanization. 

Fig. 2 a, b. Dependence of the maximum Newton viscosity (t/0) (a) and swelling ratio of the extrudate (D) (b) on the molecular mass of cis-1,4-polyisoprene, unfilled and filled to 33% by mass. Filler 1 — not 2 — CaC03 with specific surface areas 2-3 m2/g 3 — ash PM —15 with specific surface areas 12-18m2/g 4 — ash PM-100 with specific surface areas 90-100 m2/g... 

Figure 4. BR + IR is a 50/50 (wt) blend of synthetic cis-1,4-polyisoprene and cis-1,4-polybutadiene. Bl copolymers are random cis-1,4-butadiene-isoprene copolymers with the same composition. Results obtained with Rheovibron on gum vulcanizates at 110 Hz frequency.

During the last two decades, a number of diene homopolymers and copolymers have been developed to fill the diverse elastomer needs in the production of tires. The earliest developments were mainly concerned with the preparation of stereoregular cis-1,4-polyisoprene, as a substitute for natural rubber, using... 

Table 1 lists some of the homopolymers and diblock copolymers which have been employed in our experimental investigations (1-8). Particular emphasis has been placed on blends containing 1,4 polybutadiene (1,4B). In one case, 1,4B was blended with various amounts of 1,2 polybutadiene (1,2B) and the corresponding 1,2B/1,4B diblock copolymer. A second major set of samples was constructed from various combinations of 1,4B and cis 1,4 polyisoprene (1,41) and 1, 41/1,4B diblock copolymers. A large number of ternary blends were studied, the preponderence of which contained either 25%, 50% or 75% (by weight) of a selected diblock copolymer, the remainder of the blend being comprised of one or both of the corresponding homopolymers. Homopolymer blends (0% diblock) and the pure copolymers (100% diblock) were also studied in detail. 

A convenient term for any material possessing the properties of a rubber but produced from other than natural sources. A synthetic version of natural rubber has been available for many years with the same chemical formula, i.e., cis-1,4-polyisoprene, but it has not displaced the natural form. See also Butyl Rubber, Chloroprene Rubber, Ethylene-Propylene Rubber, Nitrile Rubber, Silicone Rubber and Styrene-Butadiene Rubber. 

The determination of the various types of geometric isomers associated with unsaturation in Polymer chains is of great importance, for example, in the study of the structure of modern synthetic rubbers. In table below are listed some of the important infrared absorption bands which arise from olefinic groups. In synthetic "natural" rubber, cis-1, 4-polyisoprene, relatively small amounts of 1, 2 and 3, 4-addition can easily be detected, though it is more difficult to distinguish between the cis and trans-configurations. Nuclear magnetic resonance spectroscopy is also useful for this analysis. 

Atomistic Monte Carlo Simulation of cis-1,4 Polyisoprene Melts. I. Single Temperature End-Bridging Monte Carlo Simulations. 

Natural rubber may be considered as a linear polymer of isoprene (2-methyl-1, 3-butadiene) and is also called as cis -1,4-polyisoprene. 

More recent work on hydrocarbon oligomers by T. Suzuki established the biodegradation of oligomers of cis-1,4-polyisoprene,(23) polybutadiene,(24) polyethylene,(25) and polystyrene(26). 

The structural uniformity of synthetic polymers is in general not as perfect as in the case of their natural counterparts. However, using special initiators and optimized polymerization conditions, it is possible to prepare quite homogeneous CIS-1,4-polyisoprene ( synthetic natural rubber ). 

Bristow, G.M. Relation between stress-strain behavior and equilibrium volume swelling for peroxide vulcanizates of natural rubber and cis-1,4-polyisoprene. J. Appl. Polymer Sci. 9, 1571-1578 (1965). 

The discovery that lithium and its alkyls produce a highly cis-1,4 polyisoprene in hydrocarbon solvents (103) has led to a renewed interest in metal and metal alkyl initiated polymerization. About the same time Szwarc (109) postulated an electron transfer mechanism for the initiation of polymerization by sodium naphthalene in ether solvents. This was extended to lithium metal catalysis by Tobolsky (80) and Overberger (83) and subsequently generalized to cover all alkali metal initiation, e" + M M (1) ... 

Al-Tl Catalyst for cis-1,4-Poly isoprene. Of the many catalysts that polymerize isoprene, four have attained commercial importance. One is a coordination catalyst based on an aluminum alkyl and a vanadium salt which produces />mf-l,4-polyisoprene. A second is a lithium alkyl which produces 90% j -l,4-p olyis oprene. Very high (99%) cis- 1,4-polyisoprene is produced with coordination catalysts consisting of a combination of titanium tetrachloride, TiCl4, plus a trialkylaluminum, R3A1, or a combination ofTiCl4 with an alane (aluminum hydride derivative) (86—88). 

Since emulsion polyisoprene has low or-1,4 microstructure, it has poorer physical properties than the high cis- 1,4-polyisoprene and has not been commercialized. 

Synthetic Polyisoprene Rubbers (IR). IR is a cis-1,4 polyisoprene synthetic natural rubber. However, it does not contain the non-rubber substances that are present in NR. One can differentiate between two basic types of synthetic polyisoprene by the polymerization catalyst system used. They are commonly referred to as high cis and low cis types. The high cis grades contain approximately 96-97% cis-1,4 polyisoprene. 

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