Branched hetero-polymers

Under certain conditions, however, multifunctional polycondensations produce linear or branched polymers instead of cross-linked networks. If the functional groups are favorably arranged spatially, of course, cyclization reactions occur instead of cross-linking reactions. Such cyclopolycondensations are especially important for producing polymers with hetero rings in the main chain. 

Another heterochain polymer which has received a lot of attention recently is polyaniline. This material is produced by chemical or electrochemical oxidation of aniline, and it seems likely that it is very similar to, if not always identical with, aniline black , an ill-defined material of some antiquity. The propensity of hetero-substituted aromatics to undergo coupling via intermediate radical cations is well established and, since a monosubstituted benzene is effectively a trifunctional monomer in this context, it seems likely that this product is a network or highly branched material, which would account for its unattractive handling properties. 

Hemicellulose is the second most familiar polysaccharide next to cellulose comprising one-fourth to one-third of most plant materials, and in the past twenty years hemicellu-loses have been used as feedstock for producing sugars. Hemicelluloses are mostly hetero-polysaccharides classified according to the sugar residues present, namely xylans, mannans, arabinans and galactans, which are either linear or branched polymers. The most abundant hemicellulose is (3-l->4-D-xylan, which is built from p-l->4-linked D-xylopyranosyl residue, which forms the linear backbone of the polymer. 

The second reported synthesis and application of 1,1-diphenylethylene macromonomers provided less ambiguous results and illustrated the potential of these macromonomers in synthesis of well-defined, hetero, three-armed, star-branched polymers [197, 198]. 1,1-Diphenylethylene-functionalized polystyrene macromonomers (74, 76) were prepared by the addition of poly(styr-yl)lithium with either l,3-bis(l-phenylethenyl)benzene (73, MDDPE) [198] or l,4-bis(l-phenylethenyl)benzene (75, PDDPE) [197] as shown in Eqs. (43) and (44) ... 

A star polymer may also comprise an unknown number of arms connected to the center of the cluster by addition to the reaction mass of a second, multifunctional monomer or SRU that ties all the linear growing polymer chains together into a crosslinked (microgel) core. These are sometimes called star-branch polymers. Cloutet et al., however, describe a star-branched polymer as a dendritic block polymer . A third type of star polymer comprises a dendritic core from which emanate a known number of arms. In any of these types of star polymers, the arms may be all the same, or different arms may have different compositions the latter are known variously as hetero-star, miktoarm star, or variegated star polymers. ... 

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