Polymer hydrogenous polyisoprene

The hydrogenation of unsaturated polymers like polyisoprene is based on the mobility of a soluble catalyst in the reaction medium. In the hydrogenation of such unsaturated polymers the soluble catalyst brings its active site to the C=C bonds in the polymer chain. In contrast, a heterogeneous catalyst requires that the polymer chain unfold to gain access to a catalytically active site on the surface of a metal particle. 

The hydrogenation of polyisoprene [55] provides the equivalent of poly (ethylene-a//-propylene) or PEP, typically with low levels of a 3-methyl-1-butene repeat unit due to 3,4 incorporation of isoprene during the anionic polymerization (Scheme 23.5). Hydrogenated polyisoprene is amorphous regardless of the microstructure of the polymer prior to hydrogenation. 

In the class of other homopolyolefins also can be included poly(propylene-a/f-ethylene) or hydrogenated polyisoprene, CAS 127883-08-3. The structure of the polymer is indicated below, together with that of polyethylene and polypropylene, shown for... 

There is one additional group of polymers which is derived from this chemistry, the hydrogenated polydienes. Hydrogenated polyisoprenes [41] are chemically equivalent to an alternating copolymer of ethylene and propylene when polymerized in a 1,4 configuration and would thus be expected to exhibit behaviour which is very similar to that of OCPs. Similar characteristics can be achieved with polybutadiene... 

The polymer used in the study was hydrogenated polyisoprene, i.e. alternating poly(ethylene-propylene) (PEP) and its single-end-functionalized derivatives, which were synthesized by the anionic polymerization scheme.One derivative contains a tertiary amine group capped at one end of the chain (amine-PEP). The second has a strongly polar sulphonate-amine zwitterion at the end of the chain (zwitterion-PEP). The parent PEP and its end-functionalized derivatives are model polymers, which have been well characterized previously using various experimental techniques.The ratio M y/Mn was well below 1.1 for samples in the study. 

Tanaka and co-workers [52] determined the distribution of as-1,4 and trans-1,4 units in 1,4 polyisoprenes using C-NMR spectroscopy. Thay found that c/s-1,4 and trans-1,4 units are distributed almost randomly along the polymer chain in cis-trans isomerised polyisoprenes, and that chicle is a mixture of cis-1,4 and trans-1,4 polyisoprenes. These workers [53] also investigated the C-NMR spectra of hydrogenated polyisoprenes and determined the distribution of 1,4 and 3,4 units along the polymer chain for w-butyl lithium catalysed polymers. They confirmed that these units are randomly distributed along the polymer chain. Polymers did not contain appreciable amounts of head-to-head or head-to tail 1,4 linkages. 

Raju, et al. report an extremely extensive set of measurements of the dynamic moduli of linear and star polymers in systems ranging from the moderately concentrated up to the melt(25). The complete study examined linear polymers fully hydrogenated polyisoprene, polyisoprene, polystyrene, polybutadiene, and fully hydrogenated polybutadiene, as well as three-arm and four-arm polybutadiene stars, a total of 19 polymers having molecular weights between 4.6 and 860 kDa, at various temperatures. 

Catalysts. Iodine and its compounds ate very active catalysts for many reactions (133). The principal use is in the production of synthetic mbber via Ziegler-Natta catalysts systems. Also, iodine and certain iodides, eg, titanium tetraiodide [7720-83-4], are employed for producing stereospecific polymers, such as polybutadiene mbber (134) about 75% of the iodine consumed in catalysts is assumed to be used for polybutadiene and polyisoprene polymeri2a tion (66) (see RUBBER CHEMICALS). Hydrogen iodide is used as a catalyst in the manufacture of acetic acid from methanol (66). A 99% yield as acetic acid has been reported. In the heat stabiH2ation of nylon suitable for tire cordage, iodine is used in a system involving copper acetate or borate, and potassium iodide (66) (see Tire cords). 

As with c -polyisoprene, the gutta molecule may be hydrogenated, hydro-chlorinated and vulcanised with sulphur. Ozone will cause rapid degradation. It is also seriously affected by both air (oxygen) and light and is therefore stored under water. Antioxidants such as those used in natural rubber retard oxidative deterioration. If the material is subjected to heat and mechanical working when dry, there is additional deterioration so that it is important to maintain a minimum moisture content of 1%. (It is not usual to vulcanise the polymer.)... 

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. 

As with many polymers, polyisoprene exhibits non-Newtonian flow behavior at shear rates normally used for processing. The double bond can undergo most of the typical reactions such as carbene additions, hydrogenation, epoxidation, ozonolysis, hydrohalogena-tion, and halogenation. As with the case of the other 1,4-diene monomers, many copolymers are derived from polyisoprene or isoprene itself. 

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