Terminal double bond incorporation

We will now discuss this method as applied on mostly branched radical polymerization systems involving transfer to polymer, terminal double bond incorporation, recombination termination, and random scission for both continuous and batch reactors. 

Batch Reactor, Terminal Double Bond Incorporation [15]... 

Stein166 has indicated that the reactivity of the terminal double bond of the macromonomer (112) is 80% that of VAc monomer. The kinetics of incorporation of 112 have also been considered by Wolf and Burchard175 who concluded that 112 played an important role in determining the time of gelation in VAc homopolymerization in bulk. 

In the polystyrenes produced by cationic initiators most of the chain-ends are terminal indanyl groups, and olefinic groups are rare. As this terminal indanyl group cannot be aluminated like a double bond, the amount of tritium incorporated comes only from the initial AlBr2CH2CHPh-groups and the few residual terminal double bonds and it, therefore, represents (approximately) the total number of initiated chains. 

The rationale in using these particular dienes is that only the strained double bond of dicyclopentadiene and the terminal double bond of 1,4-hexadiene undergo polymerization with Ziegler catalysts. Consequently the polymer chains contain one double bond for each molecule of dicyclopentadiene or 1,4-hexadiene that is incorporated. These double bonds later can be converted to cross-links by vulcanization with sulfur (Sections 13-4 and 29-3). 

After successful completion of all rearrangement reactions, the incorporation of the different side chains of the tetraponerines was attempted by employing a cross metathesis reaction. However, the cross metathesis of 19 and 22 with allyltrimethylsilane in the presence of 10% [Ru-1] was unsuccessful due to the formation of a carbene with low reactivity. The use of Schrock s molybdenum catalyst26 [Mo] (Figure 7) also failed to show any conversion. The terminal double bonds of 19 and 22 were assumed to be too hindered for cross metathesis. An alternative route to incorporate the different alkyl chains of the tetraponerines was necessary (Scheme 8). 

Hexadiene is utilized as a third co-monomer in ethylene/propylene elastomers. While the terminal double bond is incorporated into the polymeric chain, the internal one is not and can be cross-linked (vulcanized) to confer... 

In contrast to all of the terpenoids considered so far rubber is an all cis acyclic terpenoid. This difference is reflected in the incorporation of tritium from [2- " C,3R,4S- H]mevalonic acid but not from the (4R)-isomer. The polyprenols (118) contain both cis- and trans-double bonds. Because of their size, biosynthetic experiments are particularly suitable for determining the number of each. In most cases examined in this way, three double bonds have a trans origin [i.e. including the terminal double bond (118 n = 3)] and the remainder are cis. 

A terminal double bond, as in V, favors large deuterium incorporation at the terminal carbon (methyl group in the product), whereas the same structure with an internal double bond, as in VI, incorporates less deuterium in the methyl group. 

The Pd-catalyzed intramolecular cascade CTOss-coupling of l-halo-l,(< l)-dienynes [for 2-halo-l,(ft> l)-dienynes see Scheme 32] with a terminal double bond leads to 2-methylenecycloalkyIidenecycloalkenes (Sch ne 29), ° whereas halodienynes with the initiating iodoalkenyl unit incorporated in the chain between the alkynyl relay and the alkenyl terminator yield methylenebicycloalkadienes (Scheme 29). ° ... 

The problem of incorporation of chains with a terminal double bond (TDB) exists in polymerizations discussed above, such as radical polymerization of vinyl acetate and olefin polymerization with a constrained-geometry metallocene catalyst (CGC). Tobita [15] has developed an MC algorithm for this problem for the PVAc case. It is assumed that TDBs are created by transfer to monomer only, while recombination is absent, which results in a maximum of one TDB per chain. We largely follow Tobita s explanation, but differ in that we will assume that disproportionation is the termination mechanism, while transfer to solvent and to polymer are not yet being accounted for. Later we will address the real PVAc problem, which in fact has two branching mechanisms TDB propagation and transfer to polymer. 

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