Pendant chains

MMA onto cellulose was carried out by Hecker de Carvalho and Alfred using ammonium and potassium persulfates as radical initiators [30]. Radical initiators such as H2O2, BPO dicumylperoxide, TBHP, etc. have also been used successfully for grafting vinyl monomers onto hydrocarbon backbones, such as polypropylene and polyethylene. The general mechanism seems to be that when the polymer is exposed to vinyl monomers in the presence of peroxide under conditions that permit decomposition of the peroxide to free radicals, the monomer becomes attached to the backbone of the polymer and pendant chains of vinyl monomers are grown on the active sites. The basic mechanism involves abstraction of a hydrogen from the polymer to form a free radical to which monomer adds ... 

The structural versatility of pseudopoly (amino acids) can be increased further by considering dipeptides as monomeric starting materials as well. In this case polymerizations can be designed that involve one of the amino acid side chains and the C terminus, one of the amino acid side chains and the N terminus, or both of the amino acid side chains as reactive groups. The use of dipeptides as monomers in the manner described above results in the formation of copolymers in which amide bonds and nonamide linkages strictly alternate (Fig. 3). It is noteworthy that these polymers have both an amino function and a carboxylic acid function as pendant chains. This feature should facilitate the attachment of drug molecules or crosslinkers,... 

FIGURE 3 Schematic representation of a pseudopoly (amino acid) derived from the side chain polymerization of a dipeptide carrying protecting groups X and Y. The wavy line symbolizes a nonamide bond. In this polymer, the amino acid side chains are an integral part of the polymer backbone while the termini have become pendant chains. In the backbone, amide and nonamide bonds strictly alternate. 

Based on these monomeric building blocks a series of four structurally related poly(iminocarbonates) were synthesized carrying either no pendant chains at all [poly(Dat-Tym) ], a N-benzyloxycarbonyl group as pendant chain [poly(Z-Tyr-Tym)], a hexyl ester group as pendant chain (poly(Dat-Tyr-Hex) ], or both types of pendant chains simultaneously (poly(CTTH)] (Fig. 7). 

This series of polymers made it possible to investigate the contribution of each type of pendant chain separately. Poly(Dat-rym), the polymer carrying no pendant chains at all, was virtually insoluble in all common organic solvents. Due to its thermal instability in the molten state, poly(Dat-Tym) could be neither compression-nor injection-molded. In this respect, the processibiUty of poly(Dat-Tym) was not improved as compared to conventional poly(L-tyrosine). 

Results indicated that swelling clay stabilizers such as poly (DMA-co-EPl) which do not possess a quaternary nitrogen atom in a pendant chain may not be very effective at preventing permeability damage due to fines migration in the absence of water-swelling clays. 

Copolymers. Copolymers have also been studied (16-18). While one comonomer contains 1-2 quaternary nitrogen in a flexible pendant chain, the other comonomer was nonionic. Copolymers of the methyl chloride salt of dimethylaminoethyl methacrylate (one quaternary nitrogen atom) and dimethylaminoethyl methacrylate (DMAEMA) and of MDTHD (2 quaternary nitrogen atoms) and DMAEMA, N,N-dimethylacryl-amide (NNDMAm) or dimethylaminopropyl methacrylate (DMAPMA) have been studied and the results summarized in Table VI. 

From the chemical point of view, the rapid fluctuations mean that diffusion of solvents and reagents should be rapid, all sites on the resin readily accessible,and pendant chains easily accommodated throughout the matrix. The uniformity of physical... 

As an example, bulk modification by the organic reaction of unsaturated PHA with sodium permanganate resulted in the incorporation of dihydroxyl or carboxyl functional groups [106]. Due to the steric hindrance of the isotactic pendant chains, complete conversion could not be obtained. However, the solubility of the modified polymers was altered in such a way that they were now completely soluble in acetone/water and water/bicarbonate mixtures, respectively [106]. Solubility can play an important role in certain applications, for instance in hydrogels. Considering the biosynthetic pathways, the dihydroxyl or carboxyl functional groups are very difficult to incorporate by microbial synthesis and therefore organic chemistry actually has an added value to biochemistry. 

Recently, PHAs based on fatty acids have been crosslinked. By varying the type of fatty acid in the fermentation process, the type and amount of double bonds in the pendant chains was easily adjusted (Table 6). PHA based on coconut... 

Degradable implants, shape-memory polymers in, 22 355 Degradable-pendant-chain hydrogels, 13 741... 

PEN blow-molded bottles, 20 50-51 Pencil leads, kaolin application, 6 688t, 696 Pencils, graphite in, 12 795 PEN copolymer bottles, 20 52 Pendant cationic azo dye, 9 423 Pendant chain polymers, fullerene,... 

This route provides access to catenanes (and knotted rings) without having to thread closed cycles, sharing an important feature of the Mobius path. The more complex ring structures arise from the tangling motions of the pendant chain before formation of the four-membered ring 6 (Scheme 2). 

Fig. 24a and b. Schematic simplified representation of the basic difference between a regular a and irregular b network knots (1), chains connecting nearest-neighbor knots (2), pendant chains (3)... 

They should consist of elastically effective chains only. An elastically effective chain should connect two different crosslinks, and two such crosslinks should be tied by only one elastic chain. This means that the gel should contain no defects such as pendant chains (one end of which only is connected with a crosslink), loops (chains linked at both ends to the same crosslink), or double connections. Physical crosslinks (permanent entanglements) should be prohibited, too. 

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