Polyethylene acetylenic monomer

Fig. 20 Synthesis of cyclic polyethylene from acetylenic monomer...

Competition, at each stage in the plastics industry, is in their raw materials. Many monomers can be made from alternate raw materials such as polyvinyl chloride that may begin with either ethylene or acetylene. Most plastic products may be made from a variety of plastics such as pipe that may be extruded from PVC, polyethylene, ABS, and so on. 

An example of the way in which process competition works in the manufacture of plastics is the story of acrylonitrile. The first process for the production of this plastic was based upon the reaction between hydrogen cyanide and acetylene, both hard to handle, poisonous, and explosive chemicals. The raw material costs were relatively low as compared to materials for other monomers, but the plant investment and manufacturing costs were too high. As a result, originally acrylonitrile monomer (1950s) sold for about 30 cents per pound and the future of the material looked dim as other plastics such as polyethylene became available at much lower prices due to their lower production costs. 

In the previous papers, we reported that the radiation-induced cross-linking of polyethylene was accelerated by acetylene (4) and by the mixtures of acetylene and some fluorine-containing monomers (5). 

Thus, ethylene, obtained from petroleum or natural gas hydrocarbons, is also a monomer for the direct formation of a plastic such as polyethylene, or of an elastomer such as Ethylene-Propylene-Termonomer (EPT) rubber. Acetic arid, produced in several steps from acetylene or ethylene, is also produced directly by the oxidation of a mixture of saturated hydrocarbons (naphtha). 

Purification of olefin-rich C4 cuts, particularly from FCC, is usually performed by selective hydrogenation of undesirable amounts of 1,3-butadiene and acetylene compounds. The use of butene-1 as a monomer in the production of polybutene and comonomer in low-density polyethylene production has high technological appeal and has been the object of recent studies in the literature [2-4], To this end a C4 stream needs to be rich in butene-1 and free from the presence of 1,3-butadiene and acetylenic compounds (content of < than 10 ppm). 

Polymerizations of unsaturated monomers, such as olefins, vinyl monomers, or acetylenes, exclusively proceed as KC reaction sequences. With exception of crystalline polyethylene, the resulting polymers are thermodynamically unstable, because the corresponding cyclohexanes or benzenes are more stable, but equilibration catalysts do not exist. As soon as polymer backbones include heteroatoms, equilibration reactions become possible, and many polymers may be prepared by KC and by TC polymerizations. An interesting case is synthesis and polymerization of oxiranes. Their synthesis from )S-bromoalcohols and their polymerization via anionic or coordination insertion catalysts represent KC reactions. Yet, heating of oxiranes or poly(alkylene oxides)s with strong protic acids yields the thermodynamically more stable 1,4-dioxanes. 

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