Olefin chain growth reaction scheme

By introducing a-olefins into the polymerization system as chain transfer agents (CTAs), the molecular weight of the PNBs from theNi cation-based catalysts can be controlled the insertion of an a-olefin is immediately followed by fi-hydrogen elimination, and a vinyl-terminated PNB and a Ni hydride are formed (Scheme 16.4). The Ni hydride species serves as a starting point for another chain growth reaction. 

The first step in catalytic reactions of the Heck type is the oxidative addition of the organic halide to Pd(0) species to form an intermediate organopalladium halide constituting the Pd(II) species. This is followed by insertion of the olefinic bond and subsequent /khydrogen elimination [scheme (30)]. The catalyst is recycled by the reaction of the Pd(II)-hydride species with a base [scheme (31)]. It is worth noting here that palladium species, L2(X)Pd—ArCH=CH2, do not propagate the chain growth polymerisation of the CH2=CHArX monomer via its olefinic bond in the discussed process. 

Scheme 1 Chain growth and isomerization reactions in the a-olefin polymerization catalyzed by Pd-diimine catalyst...

In metathesis polymerization, the catalyticaUy active species is a stable metal-carbene bond that is formed between the metal and the alkene. Upon reaction with cycloalkane, a living moiety capable of chain growth is formed. The olefin metathesis reaction mechanism is shown in Scheme 3.18. 

ROMP is a chain growth polymerization that converts cydic olefins to a polymeric material in the presence of transition metal-based complexes such as Ti, Mo, W, Ta, Re, and Ru complexes (Scheme 54) 12,329-337 powerful polymerization method is broadly applicable for the preparation of well-defined polymers. Therefore, transformation reactions of both polycydic olefins such as norbomene (NB), norbona-diene, and dicyclopentadiene and low-strain cydic olefins induding cydopentene (CP) and cydoheptene allow extension of the range of attainable block copolymers. 

Chain reactions can be divided roughly into two types polymerization and nonpolymerization. In polymerizations (Scheme 6), an initiating radical (R ) adds to a substrate olefin (ordinarily termed the monomer), to yield a new radical, which adds to another olefin, and so forth. The kinetic chain, that is, the sequence of events begun by a given R- radical from the initiator, corresponds in this scheme to the actual growth of the polymer molecule, and terminates simultaneously with the growth of the molecular chain as two radicals combine or disproportionate. 

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