Base chains

Skaija GA and Woodhouse KA. S3mthesis and characteization of degradable pol)oirethane elastomers containing an amino acid based chain extender. J Biomater Sci Polym Ed, 1998, 9, 271-295. 

A surfactant was defined in Chapter 8 as an agent, soluble or dispersible in a liquid, which reduces the surface tension of the liquid [1]. It is helpful to visualise surfactant molecules as being composed of opposing solubility tendencies. Thus, those effective in aqueous media typically contain an oil-soluble hydrocarbon-based chain (the hydrophobe) and a smaller water-solubilising moiety which may or may not confer ionic character (the hydrophile). The limitations of space do not permit a comprehensive detailed treatment of the chemistry of surfactants. The emphasis is therefore on a broad-brush discussion of the principal types of surfactant encountered in textile preparation and coloration processes. Comprehensive accounts of the chemistry and properties of surfactants are available [2-13]. A useful and lucid account of the chemistry and technology of surfactant manufacturing processes is given by Davidsohn and Milwidsky [ 14] ... 

In this sub-chapter, selected examples of lanthanide-based chains are described. We have chosen to comment on only systems with structural characterization and significant dynamic properties. Chains with a sole lanthanide ion as spin carrier are described first. 3d-4f and 3d-3d -4f heterometallic chains follow. Finally, chains comprising lanthanide and radical ligands conclude this chapter. 

First attempts to obtain 3d-4f-based regular chains were made with Cu-Tb chains that show characteristic features of SCM but without structural characterization [84, 85]. Similarly, Co - Dy based chains were obtained but showed very weak x" lx ratio making the analysis of the magnetic slow relaxation difficult [86]. Lastly, some magnetic interplay between manganese oxide chains and Dy09 units... 

Table 4.2 Most relevant magnetic parameters of selected examples of lanthanide-based chains giving rise either to slow relaxation or 3D ordering. 

In real systems, the number of spin centers N is, of course, too large to deterministically solve the corresponding eigenvalue problem of a corresponding spin Hamiltonian. Thus, no exact solution exists. Several approximate expressions were developed, such as the Bonner Fisher finite-chain model for equidistant antiferro-magnetically coupled S = 1/2-based chains.20 Here, the susceptibility is calculated for finite chain segments (ca. N 10 spin centers) and extrapolated to an infinite chain (N > oo). The extrapolated expression for the susceptibility is as follows ... 

Chen J, Iannone MA, Li MS, Taylor JD, Rivers P, Nelsen AJ, Slentz-Kesler KA, Roses A, Weiner MP. A microsphere-based assay for multiplexed single nucleotide polymorphism analysis using single base chain extension. Genome Res 2000 10 549-557. 

Branched unsaturated side chains are named similarly with a number preceding the base chain to specify the position of the double or triple bond. Thus (1,3-dimethyl-2-butenyl) indicates two methyl radicals attached to a butyl radical ... 

A method for the controlled emulsion polymerization of chloroprene using dithiocarbamic esters as sulfur-based chain transfer agents is described. The method provides industrially relevant molar masses with Mn s> 50,000 daltons with good yields in acceptable times. It was further determined that when pKa values for the dithiocarbamic acid precursors were less than 12, the thioester was ineffective as a regulator. 

TABLE 1. Effect on the polymerization of chloroprene nsing selected dithiocarbamic esters as sulfnr-based chain transfer agents. 

Note An aliphatic dithiocarbamic ester acid precursor having a pKa value less than 12 was ineffective as a sulfur-based chain transfer agents. 

There is no doubt that free-radical chemistry has benefited enormously through the invention of tin-based chain-carrying reagents " . Of these, tributyltin hydride and, to a lesser extent, triphenyltin hydride have been the reagents of choice. Their ready availability and favourable rate constants for attack of the corresponding tin-centred radicals at a variety of radical precursors , coupled with useful rate constants for hydrogen transfer to aUtyl and other radicals, provide for reagents superior to their silicon counterparts only tris(trimethylsilyl)silane rivals tributyltin hydride in its synthetic utility . 

The main advantages of cationic photoinitiators is that they have high reaction rates and require a low energy. They can operate at a low temperature, they are not inhibited by oxygen, they do not promote the polymerization of epoxy groups in the dark, and they are often stable at elevated temperatures. Some disadvantages exist that is, inhibition by bases, chain-transfer reaction by water, and the presence of acids in cured products. 

Lichtenhan et al. [23,24] prepared several monosubstituted POSS epoxides (XIX). The Cs-based chain epoxy (5-9 wt%) was used with 1,4-butanediol diglycidyl ether (EDGE) (XX), diglycidyl ether of Bisphenol A (DGEBA) (XXIII) and polyoxypropylene diamines (XXI) to prepare nano-reinforced epoxy network glasses (Scheme 6) [23]. 

These three isomers differ in the lengths of their base chains but not in the functional groups present (i.e., only alkyl groups are present in this case). As a result, they differ somewhat in their melting and boiling points but differ only very slightly in the reactions they undergo. 

Parrag IC, Woodhouse KA (2010) Development of biodegradable polyurethane scaffolds using amino acid and dipeptide-based chain extenders for soft tissue engineering. J Biomater Sci Polym Ed 21(6-7) 843-862... 

Polysiloxane is described as an inert silicon-based chain polymer. Gellation is a cross-linking reaction controlled by a catalyst-inhibitor system. Gel times can be varied from minutes to hours. Cost in place per unit volume of stabilized soil is four times or more that of sodium silicate. 

Is increased considerably by the replacement of a hydrocarbon chain by a fluorocarbon- or silicone-based chain. 

It was of interest to extend the reactions of tetrols with cyclic diketones to produce a variety of spiro polymers with less oxygen in the base chain and with other functional groups present... 

Caseri, W.R. et al., "(Hot-)Water-Proof", semiconducting, platinum-based chain struc-... 

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