Polyisoprene Hydrogenation

Methyl-buta-1,3-diene, compd. with 2-methyl butane. See Polyisoprene, hydrogenated... 

Polyisoprene (hydrogenated natural rubber) is a completely alternating etbylene propylene copolymer (i.e., does not have ethylene or propylene blocking) and is therefore an interesting substance for Py-GC studies. Tbe surface area of tbe main peaks up to C13 obtained by van Schooten and Evenhuis [13, 14] indicate that the unzipping reaction which would yield equal amounts of ethylene and propylene in the hydrogenated pyrolysate takes place to some extent, but is less important than the hydrogen transfer reactions ... 

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. 

Polyisoprene can be UV or e-beam cured [43,44]. The 3,4 units are particularly prone to crosslinking at low dose [45]. SIS and SBS are also crosslinkable, even conventional linear materials with low vinyl content however, small amounts of liquid trithiol or triacrylate compounds speed cure dramatically [44]. Like UV, e-beam cure is strongly affected by tackifier choice. Hydrogenated, non-aromatic resins provide much less interference with cure [36,37]. 

B = B 4, 1,4-polybutadiene block Bj 2, 1,2-polybutadiene block B y, medium vinyl (35-60%) polybutadiene block) I, 1,4-polyisoprene block. Selective hydrogenation this block not hydrogenated. 

In this study, the effects of the variations in block sequence and composition (and thus relative block length) on the material properties of two series of triblock copolymers has been investigated. One of the blocks, the hydrogenated polybutadiene (HB), is semicrystalline, and the other block, the hydrogenated polyisoprene (HI) is rubbery at room temperature. Thus in one series, the HBIB block copolymers, the end blocks are semi-... 

The mechanism for this catalyst for the hydrogenation of ds-l,4-polyisoprene (CPIP) is slightly different [69]. As there was no clear evidence that coordination of hydrogen occurs prior to the coordination of C=C to the RuHCl(CO)(PCy3)2, there may be two possible pathways for the hydrogenation of CPIP in the presence of Ru(CH=CH(Ph))Cl(CO)(PCy3)2, namely an unsaturated path and a hydride path. The catalytic mechanism for these two pathways is represented in Scheme 19.6. 

Scheme 19.6 Proposed mechanism of e/s-l,4-polyisoprene (CPIP) hydrogenation using Ru(CH=CH(Ph))CI(CO)(PCy3)2.

The rate expression is consistent with the observed kinetic data. A similar mechanism was also proposed for the hydrogenation of polyisoprene catalyzed by 0sHCl(C0)(02)(PCy3)2 [93]. 

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. 

Figure 2.21 Most probable hydrogens attacked by oxidation a) PP resin segment, b) polypropylene glycol segment, and c) trans polyisoprene segment. The arrows point to the hydrogens that are the most susceptible to attack and removal...

Fig. 4.1 a Typical time evolution of a given correlation function in a glass-forming system for different temperatures (T >T2>...>T ), b Molecular dynamics simulation results [105] for the time decay of different correlation functions in polyisoprene at 363 K normalized dynamic structure factor at the first static structure factor maximum solid thick line)y intermediate incoherent scattering function of the hydrogens solid thin line), dipole-dipole correlation function dashed line) and second order orientational correlation function of three different C-H bonds measurable by NMR dashed-dotted lines)... 

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