Saturated polyisoprene

Notes The values of A, B, and C and thus of y are based on a reference volume Vre/ = 0.1 nm Polymer notation A d- label preceding the polymer acronym indicates a per-deuterated polymer partially deuterated polymers are labeled as dy, df, etc., for selective deuteration of 3, 4, etc., hydrogens. Numbers in subscripted parentheses after the polymer name indicate the primary comonomer fraction, e.g., SPB(6s) is a saturated polybutadiene with 66 mol% butadiene Polymer acronyms P2VP poly(2-vinyl pyridine), P4MS poly(4-methylstyrene), PBMA poly(n-butyl methacrylate), PCHA poly(cyclohexyl acrylate), PEB poly(ethyl butylene), PIB polyisobutylene, PI polyisoprene, PMMA poly(methyl methacrylate), PPMA poly(n-pentyl methacrylate), PP polypropylene, HHPP head-to-head polypropylene, PS polystyrene, PVME poly(vinyl methyl ether), PXE poly(2,6-dimethyl-l,4-phenylene oxide), SPB saturated polybutadiene, SPI saturated polyisoprene... 

Maleimides Alkyl and aryl maleimides in small concentrations, e.g., 5-10 wt% significantly enhance yield of cross-link for y-irradiated (in vacuo) NR, cw-l,4-polyisoprene, poly(styrene-co-butadiene) rubber, and polychloroprene rubber. A-phenyhnaleimide and m-phenylene dimaleimide have been found to be most effective. The solubihty of the maleimides in the polymer matrix, reactivity of the double bond and the influence of substituent groups also affect the cross-fink promoting ability of these promoters [82]. The mechanism for the cross-link promotion of maleimides is considered to be the copolymerization of the rubber via its unsaturations with the maleimide molecules initiated by radicals and, in particular, by allyfic radicals produced during the radiolysis of the elastomer. Maleimides have also been found to increase the rate of cross-linking in saturated polymers like PE and poly vinylacetate [33]. 

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

How much of a crystallizable material X can I blend uniformly into a polymer until it starts to form crystals A series of blends with increasing amount of X is prepared. The samples are studied by WAXS (cf. Sect. 8.2) using laboratory equipment. Crystalline reflections of X are observed, as X starts to crystallize. Peak areas can be plotted vs. the known concentration in order to determine the saturation limit. Think of X being Ibuprofen and Y a polystyrene-(7 )-polyisoprene copolymer, and you have an anti-rheumatism plaster. 

On the other hand, Schaefer ( ) has shown from selective saturation experiments of amorphous cis polyisoprene, crystalline trans polyisoprene, as well as carbon black filled cis polyisoprene, that the resonant lines are homogeneous. The linewidths in these cases are thus not caused by inhomogeneous broadening resulting from equivalent nuclei being subject to differing local magnetic fields. The results for these systems are thus contrary in part to what has been found here. 

The termination reactions appear to be quantitative and specific for the reaction of saturated polymer molecules attached to aluminium and titanium [116], but applied to diene polymerizations the method is less satisfactory mainly because of the greater stability of allylic carbon-transition metal bonds. Polybutadiene has been labelled by terminating with tritiated methanol with the Cr(acac)3/AlEt3 catalyst [55], and similarly polyisoprene prepared with VCl3/AlEt3 [107]. Polybutadiene prepared with Til4/Al(i-Bu)3 has been labelled using C02 [115]. 

To achieve absolutely regiospecific sulfonation, the diene inner blocks have been hydrogenated to yield a frilly saturated poly(ethylene-alt-propylene) elastomer, in the case of isoprene, and poly(ethylene-co-l-butene) in the case of butadiene. Due to ease of the linking reaction, most of the latest work has dealt with polybutadiene-based samples, and the remaining discussion will deal with them, although the reactions and techniques are also applicable to the polyisoprene-based samples. 

Albrecht, K.L. et al.. Phase equilibria of saturated and unsaturated polyisoprene in sub- and supercritical ethane, ethylene, propane, propylene and dimethyl ether. Fluid Phase Equilibria, 117, 84—91, 1996. 

The major discovery concerning polyisoprene is vulcanization, i.e. the creation of bridges between chains by means of sulphur atoms which saturate double bonds actually, this goes back to 1839, when Goodyear observed the stability of this new material. Vulcanization is a series of reactions which can be shown schematically as follows... 

It is proposed that this is due to attack of carbonyl oxides, in their biradical form, on the rubber double bonds. Typical diene rubbers (polyisoprene and polybutadiene) have rate constants several orders of magnitude greater than polymers having a saturated backbone (polyolefins). Other unsaturated elastomers having high reaction rates with ozone include styrene-butadiene (SBR) and acrylonitrile-butadiene (NBR) rubbers. As an example, Polychloroprene (CR) is less reactive than other diene rubbers, and it is therefore inherently more resistant to attack by ozone. 

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