Polyisoprenes mechanical properties

In Table 1 some of the properties of raw synthetic hj -l,4-polyisoprene (Goodyear s Natsyn) and natural mbber (Hevea) are presented along with references that contain additional thermal, optical, electrical, and mechanical property data. Some properties of synthetic /n j -l,4-polyisoprene (Kuraray TP-301) are also given. Molecular weights and mol wt distribution are determined by gel-permeation chromatography (gpc) (11). 

Zhou L.L. and Eisenberg A., lonomeric blends. II. Compatibility and dynamic mechanical properties of sulfonated cis-l,4-polyisoprenes and styrene/4-vinylpyridine copolymer blends, J. Polym. Sci., Polym. Phy., 21, 595, 1983. 

Improvement in the processing and vulcanized qualities of a range of systems have been reported over the past decades. Modification of natural rubber, due to work in the British Rubber Producers Research Association, yields some of the most striking applications of microgel. A detailed study at the MV Lomonosov Institute of Fine Chemical Technology, in Moscow, on the effect of microgels on mechanical properties of cis-polyisoprene and butadiene-styrene rubbers extensively illustrates the properties of blends from latex combination of microgel and conventional or linear systems.(31)... 

The commerical polybutadiene (a highly 1,4 polymer with about equal amounts of cis and trans content) produced by anionic polymerization of 1,3-butadiene (lithium or organolithium initiation in a hydrocarbon solvent) offers some advantages compared to those manufactured by other polymerization methods (e.g., it is free from metal impurities). In addition, molecular weight distributions and microstructure can easily be modifed by applying appropriate experimental conditions. In contrast with polyisoprene, where high cis content is necessary for suitable mechanical properties, these nonstereoselective but dominantly 1,4-polybutadienes are suitable for practical applications.184,482... 

ABA copolymers poly(methyl methacrylate)-polyisoprene-poly(methyl methacrylate) having polyisoprene with a high vinyl content as central block have been synthetized by Cole et al. 2I°. Dynamic mechanical properties of films of these ABA copolymers have been studied as a function of the copolymer composition, the temperature and the nature of the solvent (carbon tetrachloride, toluene, ethyl acetate, methylethyl ketone, dioxane) used for film preparation210. ... 

CHEMICAL MODIFICATION The following chemical modifications of cis-1,4-polyisoprene are employed as a convenient way of altering physical and mechanical properties hydrohalogenation, halogenation, oxidation, ozonolysis, hydrogenation, carbene addition, cyclization. ... 

Chemically, natural rubber is natural ds-polyisoprene. The synthetic form of natural rubber, synthetic ds-polyisoprene, is called isoprene rubber. The physical and mechanical properties of IR are similar to the physical and mechanical properties of natural rubber, the one major difference being that isoprene does not have an odor. This feature permits the use of IR in certain food-handling applications. 

Natural rubber itself is a polyisoprene (cis). By the addition of carbon black, it reaches excellent mechanical properties however, natural rubber suffers from relatively low resistance to heat, oxygen from the atmosphere (mainly to ozone), and various oils or solvents. The synthetic polyisoprene and SBR are typical rubber substitutes, resembling mbber in general performance. 

Effects of silica modifled by radiation- and thermal-induced admicellar polymerization on the mechanical properties i.e. tensile properties and tear strength of the reinforced polyisoprene were compared with those of the typical silica filled polyisoprene with and without TESPT. "... 

Many components in medical devices are made of rubber and rubber blends, consisting of latex, polyisoprene, silicone rubber, fluoroelastomers, ethylene propylene, etc. Some examples of conunercial products refer to seals for medical appliances, O-rings for dialyzers, medical pump seals, intravenous components, feeding devices, etc [http //www.applerubber.com/products/medical-seals.cfm]. However, if the concerned product interacts with tissues or biological fluids, it must fulfill some requirements referring to the biocompatibility, temperature resistance, chemical stability, mechanical properties, and electrical properties. Silicone rubber assures aU of these demands, being the most encountered type of rubber used in the fabrication of medical device parts. It is commonly used for the fabrication of different tubes and catheters because of its hemocompatibility and inert character. 

Rennar, N. Oppermann, W., Swelling Behavior and Mechanical-Properties of Endlinked Poly(dimethylsiloxane) Networks and Randomly Cross-Linked Polyisoprene Networks. Coll. Polym. Sci. 1992,270(6), 527-536. 

The earliest emulsion polymers are those found in nature. Natural rubber (NR) latexes have been extracted from the rubber tree (Hevea brasiliensis) (286) for hundreds of years. The latexes are comprised of dispersions of high molecular weight, linear cis-1,4-polyisoprene (210) particles ranging in diameter from 10 nm to several microns. Because the natural mbber particles are in a colloidal form, they must first be separated from the aqueous phase by coagulation before processing. Since the molecular structure of natural rubber is stereoregular, it has excellent mechanical properties that have not been duplicated by modem synthetic mbbers. 

Trans-l,4-polyisoprene rubber (i.e., PIR, sometimes called Gutta Percha in the past) is a synthetic rubber with properties similar to those of its natural counterpart It was first industrially prepared during World War 11 because of a lack of supply of natural rubber but despite containing fewer impurities than natural rubbers and having a simpler preparation process it is not widely used because it is also more expensive. Mechanical properties and chemical resistance is identical to that of natural rubber. As with many other rubbers its mechanical properties can be also improved by the vulcanization process. 

Stereoregularity is of importance in some cases. Polyisoprenes are available with cis-isoprene contents between 92% and 98%. This influences the processing and mechanical properties of the compound substantially. Similarly, SBR are available as random or block copolymers with different configurations. These influence strength, rolling resistance and wet skid properties of tyres. In emulsion polymers, the type of coagulation system and stabiliser added influences the end-application. Similarly, the type and level of oil and/or carbon black extension of specific grades of polymer must be controlled. 

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