Natural rubber halogenation

As natural rubber is a product of nature, its properties are determined by the biochemical pathway by which the polymer is synthesized in the plant. In the case of natural rubber the polymerization process cannot be tailored like that of synthetic rubbers. The only option to modify natural rubber is after it has been harvested from the tree. The important modified forms of natural rubber include hydrogenated natural rubber, chlorinated natural rubber, hydro-halogenated natural rubber, cyclized natural rubber, depolymerised liquid natural rubber, resin modified natural rubber, poly(methyl methacrylate) grafted natural rubber, poly(styrene) grafted natural rubber, and epoxidized natural rubber [33,34]. Thermoplastic natural rubber prepared by blending natural rubber and PP is considered as a physically modified form of natural rubber. 

The empirical formula of halogenated natural rubber is C5H8CI3.5. This strongly suggests that the chlorination reaction involves more than one isoprene unit and, since the products are soluble, cyclization rather than cross-linking is indicated. 

Like NR, SBR is an unsaturated hydrocarbon polymer. Hence unvulcanised compounds will dissolve in most hydrocarbon solvents and other liquids of similar solubility parameter, whilst vulcanised stocks will swell extensively. Both materials will also undergo many olefinic-type reactions such as oxidation, ozone attack, halogenation, hydrohalogenation and so on, although the activity and detailed reactions differ because of the presence of the adjacent methyl group to the double bond in the natural rubber molecule. Both rubbers may be reinforced by carbon black and neither can be classed as heat-resisting rubbers. 

Reaction of the natural rubber hydrocarbon with hydrochloric acid yields rubber hydrochloride. The hydrogen chloride adds on according to Markownikoff s rule (that the halogen atom attaches itself to the carbon atom with the least number of hydrogen atoms). 

The standard polymers used for rubber linings consist of materials that are cross-linkable macromolecules which, on mixing with suitable reactants that form strong chemical bonds, change from a soft deformable substance into an elastic material. These polymers include natural rubber and its corresponding synthetic, c/s-polyisoprene, styrene-butadiene rubber, polychloroprene, butyl rubber, halogenated butyl rubbers, acrylonitrile-... 

Natural rubber Styrene-butadiene rubber Polybutadiene Polyisoprene Nitrile rubber Halogenated nitrile rubber Ethylene-propylene rubber EPDM... 

Natural rubber is resistant to dilute mineral acids, alkahes, and salts, but oxidizing media, oils, and most organic solvents will attack it. Hard rubber is made by adding 25 percent or more of sulfur to natural or synthetic rubber and, as such, is both hard and strong. Chloroprene or neoprene rubber is resistant to attack by ozone, sunlight, oils, gasoline, and aromatic or halogenated solvents but is... 

When the polymeric initiator contains many halogens, there will be many grafted side chains, and the product is called a comb or brush polymer. A variety of polymers can be used as the polymeric initiator, including polymers containing vinyl chloride and 4-chloromethylstyrene units, and halogenated natural and butyl rubbers. Graft copolymers are discussed further in Chaps. 5, 6, and 9. 

The resilience of gum neoprene vulcanizates is little lower than natural rubber but it decreases with increased filler incorporation. Therefore, the resilience of most practical neoprene compounds is higher than that of natural rubber with comparable volume loading. Because of the presence of chlorine in the neoprene molecule, products made from neoprene resist combustion to a greater degree than products made from non-halogen bearing rubbers. This means neoprene can be compounded to meet the flammability requirements of the Mine Safety and Health Administration (MSHA) USA or similar requirements as might be stipulated by any other countries,... 

The above units are randomly arranged in emulsion copolymers, but in solution the polymers may occur in uniform blocks of varying length. These block copolymers are resilient and rubber-like at room temperature, but are thermoplastic at higher temperatures. SBRs are similar to natural rubber, in that they are susceptible to atmospheric oxidation and ozone cracking when stretched in air. They are swollen and weakened by hydrocarbons and halogenated hydrocarbons. However, their resistance to abrasion and ageing is superior to natural rubber. 

Halogens HF absorbers, fluoride dryer, centrifuges Natural rubber, ebonite, semi-ebonite... 

Earlier accounts of the reaction of halogenated products with potassiiun sulfide did not report useful polymeric products [10]. Patrick and Mnookin [11] were the first to report useful polysulfide products that were to become the early basis of the Thiokol Chemical Corp. business. Polysulfides generated interest before and after World War II because natural rubber was difficult to obtain at times and was also high in price [12]. 

Alkali and acid treatments have also been used to modify surface properties of polymers sulfonated polyethylene films treated first with ethylenediamine and then with a terpolymer of vinyhdene chloride, acrylonitrile, and acrylic acid exhibited better clarity and scuff resistance and reduced permeabihty. Permanently amber-colored polyethylene containers suitable for storing light-sensitive compoimds have been produced by treating fluorosulfonated polyethylene with alkali. Poly(ethylene terephthalate) dipped into trichloroacetic/chromic acid mixture has improved adhesion to polyethylene and nylons. Antifogging lenses have been prepared by exposing polystyrene films to sulfonating conditions. Acid and alkali surface treatments have also been used to produce desired properties in polymethylmethacrylates, polyacrylonitrile, styrene-butadiene resins, polyisobutylene, and natural rubber. Surface halogenation of the diene polymers natural rubber and polyisobutylene resulted in increased adhesion to polar surfaces. 

---