Frans-Piperylene

The explanations for the relative rates of reaction have been based on three factors (1) The rate of reaction increases as the electron density in the diene system increases thus isoprene reacts faster than butadiene and a complex electron-rich 2-silylmethylbutadiene reacts even faster. (2) The rate of reaction increases as the steric hindrance due to the diene substituents decreases thus frans-piperylene reacts more slowly than dimethylbu-tadiene or isoprene. (3) A decrease in the equilibrium concentration of the cisoid conformer results in a slower reaction rate thus cw-piperylene or cis/trans-2,4-hexadiene react more slowly than /rans-piperylene or transltrans-2,4-hexadiene, respectively.175177... 

From the cyclodimerization of m-piperylene all four possible isomers of dimethylcyclooctadiene, (XLVIII)-(LI), may be isolated. frans-Piperylene,... 

Phosphonodithioic anhydrides react regioselectively with unsymmetri-cal dienes to give Diels-Alder adducts.24 For example, isoprene and frans-piperylene react to form adducts shown in Scheme 6-1V. Yields... 

It is known [66] that in frans-piperylene the methyl group does not prevent the molecule from adopting the cisoid conformation ... 

The small chain hydrocarbon tackifiers are oligomers with molecular weights in the range of several hundred to 2000 g/mol. They are typically obtained from petroleum feed streams and fall into three general classes. The most common C-5 aliphatic hydrocarbons are cis- and frans-piperylene and isoprene. 

Cycloaddition and ene reactions. Dienes >C=C—C=C< such as buta-1,3-diene, isoprene, 2,3-dimethylbuta-l,3-diene, fran -piperylene, cyclopentadiene or anthracene react with 92 in Diels-Alder fashion to give [2 - - 4] cycloadducts 410 (equation 128) . Ene products 411 are formed additionally when the relative reaction rates for the [2 + 4] cycloaddition reaction and the ene reaction are comparable (e.g. for isoprene and 2,3-dimethyl-l,3-butadiene) Alkenes with allylic hydrogen (propene, 2-butene, isobutene) give ene products see equation 129. 

A review of the cycloaddition reactions of o-benzoquinones as carbodiene, heterodiene, dienophile, or heterodienophile has been published. In the Diels-Alder reaction of furans with masked o-benzoquinones (145), the furans unexpectedly behaved as dienophiles to yield cycloadducts (146) (Scheme 56). Masked benzoquinones behave as dienes which undergo Diels-Alder reactions with electron-rich dienophiles such as enol ethers and thienol ethers.The asymmetric Diels-Alder reactions of 5-substituted and 5,6-disubstituted (S)-2-(p-tolylsulflnyl)-l,4-benzoquinones with cyclopentadiene and fran -piperylene show complete regio- and jr-facial selectivities. The hetero-Diels-Alder reactions of o-benzoquinones with tetracyclone produce cyclopenta[I ][l,4]benzodioxinone derivatives in high yield. 

Proceeding from the above considerations it should be assumed that trans-piperylene behaves in polymerization according to the curve for the s-cis-conformation in Fig. 4, whereas the behavior of eis-piperylene corresponds to the curve of the s-frans-conformation. The available literature data reviewed in detail in Ref. [67] (see also Refs. [49, 68]) confirm this assumption. Moreover, this assumption is in an agreement with the fact that in isoprene polymerization the monomer form complexed with tetramethylene diamine is less reactive than the non-solvated form [69]. 

A strain-crystallizing material like NR shows much better autohesion. It can be processed to a relatively low viscosity for easy wetting on contact, and still exhibit green strength due to strain-induced crystallization. Several other strain-crystallizable elastomers have been synthesized and shown to exhibit autohesion and green strength comparable or superior to that of NR. These include rran.s-polypen-tenamer, fran -butadiene-piperylene elastomers, and uranium-catalyzed polybutadiene. 

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