Polyisoprenes properties

The use of alkaU metals for anionic polymerization of diene monomers is primarily of historical interest. A patent disclosure issued in 1911 (16) detailed the use of metallic sodium to polymerize isoprene and other dienes. Independentiy and simultaneously, the use of sodium metal to polymerize butadiene, isoprene, and 2,3-dimethyl-l,3-butadiene was described (17). Interest in alkaU metal-initiated polymerization of 1,3-dienes culminated in the discovery (18) at Firestone Tire and Rubber Co. that polymerization of neat isoprene with lithium dispersion produced high i7j -l,4-polyisoprene, similar in stmcture and properties to Hevea natural mbber (see ELASTOLffiRS,SYNTHETic-POLYisoPRENE Rubber, natural). 

The physical properties of any polyisoprene depend not only on the microstmctural features but also on macro features such as molecular weight, crystallinity, linearity or branching of the polymer chains, and degree of cross-linking. For a polymer to be capable of crystallization, it must have long sequences where the stmcture is completely stereoregular. These stereoregular sequences must be linear stmctures composed exclusively of 1,4-, 1,2-, or 3,4-isoprene units. If the units are 1,4- then they must be either all cis or all trans. If 1,2- or 3,4- units are involved, they must be either syndiotactic or isotactic. In all cases, the monomer units must be linked in the head-to-tail manner (85). 

Between the 1920s when the initial commercial development of mbbery elastomers based on 1,3-dienes began (5—7), and 1955 when transition metal catalysts were fkst used to prepare synthetic polyisoprene, researchers in the U.S. and Europe developed emulsion polybutadiene and styrene—butadiene copolymers as substitutes for natural mbber. However, the tire properties of these polymers were inferior to natural mbber compounds. In seeking to improve the synthetic material properties, research was conducted in many laboratories worldwide, especially in the U.S. under the Rubber Reserve Program. 

The Ekestone group also polymerized 1,3-butadiene to give an extremely high mol wt polybutadiene of 70% cis-1 4 stmcture. In thek research, they purposefully avoided the preparation of vinyl stmctures in both polyisoprene and polybutadiene since it was beheved that vinyl groups adversely affected tke performance. Since natural mbber was 99.9% cis-1 4 stmcture and had superior properties, they beheved that a 1,4 stmcture was necessary for acceptable physical properties. The addition of polar compounds to the hthium-catalyzed polymerization of butadiene changes the microstmcture from the 90% tij -l,4 stmcture to a mixed cis-1 4 and trans-1 4 microstmcture. 

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). 

Since emulsion polyisoprene has low cis-1,4- microstmcture, it has poorer physical properties than the high t7r-l,4-polyisoprene and has not been commercialized. 

Property polyisoprene) (GR-S) (polyisoprene) (nitrile) (neoprene) isoprene) Polybutadiene Polysulfide (polysiloxane)... 

The coagulated material consists of about 50% polyisoprene and the remainder is primarily composed of resins. Deresinated balata has been used as an alternative to gutta pereha, which it resembles in properties and also in belting applications. It is still used for making high-quality golf ball covers but for the cheaper balls it has now been replaced almost entirely by the ionomers (see Chapter 11). 

Both side groups and carbon-carbon double bonds can be incorporated into the polymer structure to produce highly resilient rubbers. Two typical examples are polyisoprene and polychloroprene rubbers. On the other hand, the incorporation of polar side groups into the rubber structure imparts a dipolar nature which provides oil resistance to these rubbers. Oil resistance is not found in rubber containing only carbon and hydrogen atoms (e.g. natural rubber). Increasing the number of polar substituents in the rubber usually increases density, reduces gas permeability, increases oil resistance and gives poorer low-temperature properties. 

IBI 1,4-Polyisoprene 1,4-Polybutadiene Poly(ethylene-co- propylene Polyethylene Inverse block polymer— properties dependent on composition... 

The glass transition temperatures (Tg) of both modified and unmodified PSs were determined by DSC analysis, and thermomechanic analysis was controlled by TMK. The results are given in Table 8. It is seen from Table 8 that the highest glass transition temperature (410 K) was obtained with chlorohydrinated PS and that of the lowest (370 K) with olefinic PS. The lowest glass transition temperature in the alkenylated PS caused to elasticity properties on polybutadien and polyisopren fragments. 

Polyisoprene is a synthetic polymer (elastomer) that can he vulcanized hy the addition of sulfur. cis-Polyisoprene has properties similar to that of natural ruhher. It is characterized hy high tensile strength and insensitivity to temperature changes, hut it has low abrasion resistance. It is attacked hy oxygen and hydrocarbons. 

Fetters L.J. and Morton M., Synthesis and properties of block pol3miers. I. Poly(a-methylstyrene)-polyisoprene-poly(a-methylstyrene). Macromolecules, 2, 453, 1969. 

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. 

Yanez-Flores et al. have studied the shear properties of blends of PE with polyisoprene rubber (Guayule mbber) [50]. The blends were prepared using a cam-type mixer at 50 rpm for 10 min at 140°C. The blend compositions ranged from 10% to 70% mbber content. 

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