Polymers unsaturated hydrocarbons

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. 

Figure 3 Comparison of chemiluminescence runs from saturated and unsaturated hydrocarbon polymers having tertiary carbons (polypropylene, polyisoprene) in the main chain.

As another case study a process synthesis of an emulsion polymerization process is given (Hurme and Heikkila, 1998). In emulsion polymerization unsaturated monomers or their solutions are dispersed in a continuous phase with the aid of an emulsifier and polymerized. The product is a dispersion of polymers and called a latex. The raw materials are highly flammable unsaturated hydrocarbons and the reaction is exothermic which both cause a risk. The main phases and systems in an emulsion polymerization plant are listed in Table 31. 

The polymerization products of propylene have been observed to be saturated hydrocarbon polymers and terpenelike unsaturated hydrocarbons (Kuhn, 64). The condensation of formaldehyde with phenols and cyclohexanols by means of aqueous hydrogen fluoride has also been observed (Badertscher el al., 65). 

The role of gas phase initiation processes was further explored by Tibbitt et al. . These authors proposed that the polymerization of unsaturated hydrocarbons in a 13.56 MHz plasma is initiated by free radicals formed in the gas by electron-monomer collisions, the initiation reactions listed in Table 6. Moreover, it was assumed that the formation of free radicals on the polymer surface due to the impact of charged particles could be neglected. This assumption is supported by the fact that at 13.56 MHz and pressures near one torr the discharge frequency is significantly greater than either f, or f and that as a result the fluxes of charged particles to the electrode surfaces are quite small. 

Unsaturated hydrocarbons are important industrial raw materials in the manufacture of chemicals and polymers. Moreover, they are valuable constituents in high-octane gasoline produced mainly through cracking of larger alkanes, although, as... 

Because of its chemical and practical significance, polymerization is exhaustively reviewed and excellent monographs,114-129 a multivolume encyclopedia,130 as well as the series Advances in Polymer Science,131 cover all aspects of the field. Consequently, our aim is not a comprehensive treatment, but to discuss the most important general aspects of the major types of polymerization of unsaturated hydrocarbons and to give selected examples of practical significance. 

Unsaturated hydrocarbons are more likely to form polymers by addition reactions than are saturated hydrocarbons. Explain why. 

Step growth reactions involving the homo- and heteropolycondensation of various bifunctional unsaturated monomers in the presence of transition metal-based coordination catalysts have appeared to be a very useful synthetic tool for the preparation of low and high molecular weight polymers with an unsaturation in the polymer backbone. These reactions lead to unsaturated hydrocarbon and non-hydrocarbon polymers where polymeric chains are formed by carbon-carbon and carbon-heteroatom coupling respectively. 

As an example of low-temperature catalytic reactions, hydrogenation of unsaturated hydrocarbons is the most important industrial application. Chemical industrial needs are mainly for unsaturated hydrocarbons, which have reactivities that enable polymer or petrochemical product development. All the processes developed for the production of olefins, diolefins, and aromatics give a mixture of unsaturated hydrocarbons, which are not valuable as such further hydrogenations are necessary to obtain usable products for refining and chemical industry. Sulfur is generally considered to be a poison of hydrogenation catalysts. But in the case of hydrodehydrogenation reactions, this compound can also be used as a modifier of selectivity or even, in some cases, as an activator. 

This is the reaction by which polymers are formed. These are unsaturated hydrocarbons which contain... 

The breakage of the polymer chain is the most probable at the allyl position to double bonds, forming primary macroradicals in unsaturated hydrocarbon chain polymers. The deplacement of the primary radical site is carried on through the rearrangement of the C=C double bonds, producing monomer or cyclic dimer and reproducing the primary macroradicals (4 and 5) according to Scheme 12.4. 

Scheme 12.4 Free radical decomposition of unsaturated hydrocarbon chain polymers through rearrangement of bonds at the macroradical end. X=H in BR, X=methyl in NR. 5-4, when X=H (in BR)...

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... 

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