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Addition-abstraction polymerization

Cases of addition-abstraction" polymerization have also been reported where propagation occurs by a mechanism involving sequential addition and intramolecular 1,5-hydrogen atom transfer steps (Section 4.4.3.4). [Pg.208]

H) Addition-abstraction polymerization Several examples of addition-abstraction polymerization have been reported. In these polymerizations, the monomers are designed to give quantitative rearrangement of the initially formed adduct via 1,5-hydrogen atom transfer (Scheme 40). The monomers (38) are such that the double bond is electron rich (vinyl ether) and the site for 1,5-H transfer is electron deficient. This arrangement favors intramolecular abstraction... [Pg.80]

For isoprene rubber, the abstraction route predominates over radical addition. Two polymeric free radicals then unite to give a crosslink. [Pg.372]

For isoprene rubber, the abstraction route predominates over radical addition. Two polymeric free radicals then unite to give a cross-link. Cross-links could also form by a chain reaction that involves the addition of polymeric free radicals to double bonds. [Pg.249]

The reaaions of the radicals (whether primary, secondary, solvent-derived, etc.) with monomer may not be entirely regio-or chemoselective. Reactions, such as head addition, abstraction, or aromatic substitution, often compete with tail addition. In the sections that follow, the complexities of the initiation process will be illustrated by examining the initiation of polymerization of two commercially important monomers, S and methyl methacrylate (MMA), with each of three commonly used initiators, azobisisobutyronitrile (AIBN), dibenzoyl peroxide (BPO), and di-t-butyl peroxyoxalate (DBPOX). The primary radicals formed from these three initiators are cyanoisopropyl, benzoyloxy, and t-butoxy radicals, respectively (Scheme 7). BPO and DBPOX may also afford phenyl and methyl radicals, respectively, as secondary radicals. [Pg.64]

Without other alternatives, the carboxyalkyl radicals couple to form dibasic acids HOOC(CH)2 COOH. In addition, the carboxyalkyl radical can be used for other desired radical reactions, eg, hydrogen abstraction, vinyl monomer polymerization, addition of carbon monoxide, etc. The reactions of this radical with chloride and cyanide ions are used to produce amino acids and lactams employed in the manufacture of polyamides, eg, nylon. [Pg.113]

Osmium carbonyl (Os3(CO)i2) acts as a photoinitiator of vinyl polymerization [20], which can function without a halide additive. The mechanism of photoinitiation is by a hydrogen abstraction from monomer to pho-... [Pg.246]

The S-S linkage of disulfides and the C-S linkage of certain sulfides can undergo photoinduced homolysis. The low reactivity of the sulfur-centered radicals in addition or abstraction processes means that primary radical termination can be a complication. The disulfides may also be extremely susceptible to transfer to initiator (Ci for 88 is ca 0.5, Sections 6.2.2.2 and 9.3.2). However, these features are used to advantage when the disulfides are used as initiators in the synthesis of tel ec he lies295 or in living radical polymerizations. 96 The most common initiators in this context are the dithiuram disulfides (88) which are both thermal and photochemical initiators. The corresponding monosulfides [e.g. (89)J are thermally stable but can be used as photoinitiators. The chemistry of these initiators is discussed in more detail in Section 9.3.2. [Pg.103]

Thus, even if /-amyloxy radicals (101) show similar specificity for addition 1 5-abstraction to /-butoxy radicals, abstraction will be of lesser importance.42"42 The reason is that most /-amyloxy radicals do not react directly with monomer. They undergo [3-scission and initiation is mainly by ethyl radicals. Ethyl radicals are much more selective and give addition rather than abstraction. This behavior has led to /-amyl peroxides and peroxyesters being promoted as superior to the corresponding /-butyl derivatives as polymerization initiators.423... [Pg.124]

Abstract Many similarities between the chemistry of carbon and phosphorus in low coordination numbers (i.e.,CN=l or 2) have been established. In particular, the parallel between the molecular chemistry of the P=C bond in phosphaalkenes and the C=C bond in olefins has attracted considerable attention. An emerging area in this field involves expanding the analogy between P=C and C=C bonds to polymer science. This review provides a background to this new area by describing the relevant synthetic methods for P=C bond formation and known phosphorus-carbon analogies in molecular chemistry. Recent advances in the addition polymerization of phosphaalkenes and the synthesis and properties of Tx-con-jugated poly(p-phenylenephosphaalkene)s will be described. [Pg.107]

Abstract During the past decade, atom transfer radical polymerization (ATRP) has had a tremendous impact on the synthesis of macromolecules with well-defined compositions, architectures, and functionalities. Structural features of copper and copper(II) complexes with bidentate, tridentate, tetradentate, and multidentate nitrogen-based ligands commonly utilized in ATRP are reviewed and discussed. Additionally, recent advances in mechanistic understanding of copper-mediated ATRP are outlined. [Pg.221]


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See also in sourсe #XX -- [ Pg.212 , Pg.268 ]




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Abstraction Addition

Addition polymerization

Additional polymerization

Additives polymerization

Polymeric additives

Propagation addition-abstraction polymerization

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