Polyisoprene rubber/plastic

The polymers of rubber plastics have unsaturated hydrocarbon chain structure, since they are polymerized from alkadienes. The general formula of poly(l,3-butadiene) or butadiene rubber (BR) and polyisoprene or natural rubber (NR) is drawn in Scheme 12.5, where X is hydrogen in BR and methyl group in synthetic polyisoprene or NR. The free radical mechanism of thermal decomposition starts by homolytic scission of the alkyl C-C bonds. Two primary macroradicals (4 and 5) are formed for which the rearrangement... 

Other polymers used in the PSA industry include synthetic polyisoprenes and polybutadienes, styrene-butadiene rubbers, butadiene-acrylonitrile rubbers, polychloroprenes, and some polyisobutylenes. With the exception of pure polyisobutylenes, these polymer backbones retain some unsaturation, which makes them susceptible to oxidation and UV degradation. The rubbers require compounding with tackifiers and, if desired, plasticizers or oils to make them tacky. To improve performance and to make them more processible, diene-based polymers are typically compounded with additional stabilizers, chemical crosslinkers, and solvents for coating. Emulsion polymerized styrene butadiene rubbers (SBRs) are a common basis for PSA formulation [121]. The tackified SBR PSAs show improved cohesive strength as the Mooney viscosity and percent bound styrene in the rubber increases. The peel performance typically is best with 24—40% bound styrene in the rubber. To increase adhesion to polar surfaces, carboxylated SBRs have been used for PSA formulation. Blends of SBR and natural rubber are commonly used to improve long-term stability of the adhesives. 

As of this date, there is no lithium or alkyl-lithium catalyzed polyisoprene manufactured by the leading synthetic rubber producers- in the industrial nations. However, there are several rubber producers who manufacture alkyl-lithium catalyzed synthetic polybutadiene and commercialize it under trade names like "Diene Rubber"(Firestone) "Soleprene"(Phillips Petroleum), "Tufdene"(Ashai KASA Japan). In the early stage of development of alkyl-lithium catalyzed poly-butadiene it was felt that a narrow molecular distribution was needed to give it the excellent wear properties of polybutadiene. However, it was found later that its narrow molecular distribution, coupled with the purity of the rubber, made it the choice rubber to be used in the reinforcement of plastics, such as high impact polystyrene. Till the present time, polybutadiene made by alkyl-lithium catalyst is, for many chemical and technological reasons, still the undisputed rubber in the reinforced plastics applications industries. 

Natural rubber - [RUBBERCOMPOUNDING] (Vol 21) - [ELASTOMERS, SYNTHETIC - SURVEY] (Vol 8) -in adhesives [ADHESIVES] (Vol 1) -cellular forms [FOAMED PLASTICS] (Vol 11) -compared to polyisoprene [ELASTOMERS SYNTHETIC - POLYISOPRENE] (Vol 9) -fluonnahon of [FLUORINECOMPOUNDS,ORGANIC - DIRECTFLUORINATION] (Vol 11)... 

A good elastomer should not undergo plastic flow in either the stretched or relaxed state, and when stretched should have a memory of its relaxed state. These conditions are best achieved with natural rubber (ds-poIy-2-methyl-1,3-butadiene, ds-polyisoprene Section 13-4) by curing (vulcanizing) with sulfur. Natural rubber is tacky and undergoes plastic flow rather readily, but when it is heated with 1-8% by weight of elemental sulfur in the presence of an accelerator, sulfur cross-links are introduced between the chains. These cross-links reduce plastic flow and provide a reference framework for the stretched polymer to return to when it is allowed to relax. Too much sulfur completely destroys the elastic properties and produces hard rubber of the kind used in cases for storage batteries. 

Block copolymers themselves are also finding rapidly expanding applications on an industrial scale. A sandwich copolymer (triblock) with an elastomeric core (polybutadiene, polyisoprene, etc.) and plastomeric ends (polystyrene, etc.) represents a physically vulcanizing rubber (plastomeric elastomer). It can be processed above the glass transition temperature of the plastomeric blocks by work-efficient technologies (injection molding, extrusion, etc.). At temperatures below the Tg of the plastic blocks, the copolymer behaves as vulcanized rubber. 

NOTE Ibtals for plastics are for those products listed and exclude some small-volume plastics. Synthetic rubber data include Canada. Dry-weight basis unless otherwise specified Density 0.940 and below " Data include Canada from 2001 Density above 0.940 Data include Canada from 1995 Data include Canada from 2000 Data include Canada from 1994 Includes styrene-butadiene copolymers and othm styrene-based polymers Unmodified Includes butyl styrene-butadiene rubber latex, nitrile latex, polyisoprene, and miscellaneous others. SOURCES American Plastics Council, International Institute of Synthetic Rubber Producers. 

All rubbers, glasses, and plastics are polymers. You are probably familiar with natural polymers like cellulose (the building block of plant fibers) and synthetic polymers like polyethylene (plastic milk cartons), polyisoprene (automobile tires), polyethylene terephthalate (soft drink bottles), polymethyl methacrylate (Plexiglas ), polyvinylidene chloride (transparent plastic wrap), polytetrafluoroethylene (Teflon ), and various polyesters (fabrics). Polyvinyl chloride, the polymer shown earlier, is used to make rigid pipes, house siding, and protective coverings for automobile seals and dashboards, among many other applications. 

Elastomers include natural rubber (polyisoprene), synthetic polyisoprene, styrene-butadiene rubbers, butyl rubber (isobutylene-isoprene), polybutadiene, ethylene-propylene-diene (EPDM), neoprene (polychloroprene), acrylonitrile-butadiene rubbers, polysulfide rubbers, polyurethane rubbers, crosslinked polyethylene rubber and polynorbomene rubbers. Typically in elastomer mixing the elastomer is mixed with other additives such as carbon black, fillers, oils/plasticizers and accelerators/antioxidants. 

These tests, however, do not identify certain chemically very inert plastics such as polyethylene, polypropylene, polyisobutylene, polystyrene, polymethyl methacrylate, polyacrylates, polyethylene terephthalate, natural rubber, butadiene rubber, polyisoprene, and silicones. Their identification requires specific individual reactions, described in Chapter 6. 

In contrast to natural rubber (cis-polyisoprene), gutta-percha (trans-poly-isoprene) is rather hard, but not brittle, and only a little elastic. It softens at about 30 °C, becomes plastic at 60 °C, and melts under decomposition at 100°C. 

Gutta-percha. The name, derived from Malayan ge-tah pertcha=latex of the percha tree, for a natural rubber (structure, see there) from the gutta-percha trees Palaquium gutta and P. oblongifolia, Sapotaceae) with properties similar to those of balata. In Sumatra, Java, and south east India, the rapidly coagulating latex of incised trees is collected, rapidly kneaded, and marketed as raw G. Pure G. is the all-trans-isorntr of polyisoprene, related to balata molecular mass ca. 100000. In contrast to the cis-isomeric natural rubber, G. is hard and less elastic but not brittle, it softens at 25-30°C, becomes plastic at 60 °C, and melts at >100°C with decomposition and formation of a sticky mass. For uses, see literature. 

National Plastics Center Museum National Plastics Exhibition (SPI) natural rubber (polyisoprene)... 

Uses Catalyst in mfg. of rubbers and plastics based on styrol-butadiene, polyisoprene, and polybutadiene initiator in anionic polymerization of styrene and conjugated dienes, thermoplastic elastomers organic synthesis... 

Polymers may be further classified as cis-isomer and tram-isomer, based on the geometrical isomerism of the repeating units. Examples are cis-, 4-polyisoprene (natural rubber) and tram-1,4-polyisoprene (Gutta percha, plastic). There are also three different classifications of polymers based on the chemical constituents present in the structures. 

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