Chain-Length Variations

Fats and oils may be synthesized in enantiomerically pure forms in the laboratory (30) or derived from vegetable sources (mainly from nuts, beans, and seeds), animal depot fats, fish, or marine mammals. Oils obtained from other sources differ markedly in their fatty acid distribution. Table 2 shows compositions for a wide variety of oils. One variation in composition is the chain length of the fatty acid. Butterfat, for example, has a fairly high concentration of short- and medium-chain saturated fatty acids. Oils derived from cuphea are also a rich source of capric acid which is considered to be medium in chain length (32). Palm kernel and coconut oils are known as lauric oils because of their high content of C-12 saturated fatty acid (lauric acid). Rapeseed oil, on the other hand, has a fairly high concentration of long-chain (C-20 and C-22) fatty acids. 

By varying the molecular stmcture, it is possible to synthesize dye initiators with the requited characteristics. The synthesis of polymethine dyes with different chain length, end groups, and substituents, or with other variations of the chromophore, has been summarized (3,4,9,21,73,74) (see also Cyanine dyes). 

By a variation of chemistry and/or chain length the different time regimes can be shifted. From a simulation point of view we are again faced by the decision what kind of information we want to get out of the simulation. If one wants to look at very local properties, depending on the local chemistry of the individual monomers, there is no way around a simulation with all chemical details. However, one should keep in mind that by such a technique it is impossible to equilibrate the system near the glass transition temperature. 

Methods for measurement of kp have been reviewed by Stickler,340 41 van Herk Vl and more recently by Beuermann and Buback.343 A largely non critical summary of values of kp and k, obtained by various methods appears in the Polymer Handbook.344 Literature values of kp for a given monomer may span two or more orders of magnitude. The data and methods of measurement have heen critically assessed by IUPAC working parties"45"01 and reliable values for most common monomers are now available. 43 The wide variation in values of kp (and k,) obtained from various studies docs not reflect experimental error but differences in data interpretation and the dependence of kinetic parameters on chain length and polymerization conditions. 

The predicted variations of F, L, and cp(r) with tethering density and chain length for each of the geometries considered are summarized in Table 1. 

The freely-jointed chain considered previously has no internal restraint, and hence, its internal energy is zero regardless of its present configuration. The entropy (S) is not constant, however, since the number of available configurations decreases with the chain end separation distance. The variation which follows from chain length change by a small amount (dr) at constant temperature (T) is given by the Boltzmann rule of statistical thermodynamics ... 

In the sulfosuccinate esters a comparable hydrophobic part consists of the fatty chain plus the functionalities introduced by maleic acid anhydride function. The product variation would then be possible by changing the chain length and/or degree of saturation of the fatty alcohol. The fatty alcohol itself can be replaced by an ethoxylated fatty alcohol with different degrees of ethoxylation as another parameter to be varied. 

Other lipophilic groups possibly attached to the maleic acid anhydride are alkanolamides of fatty acids. In this case the variations could be chain length and/or saturation grade of the C chain, the type of alkanolamine (most common are isopropanolamine, monoethanolamine, and diglycolamine), or an etho-... 

Variation of Toxicity of Monoalkyltin Trichlorides with Alkyl Chain Length (470, 499)... 

The variations of film thickness and the contact angle value of FDTS SAM are also closely related to the immersing time as shown in Fig. 22. The film thickness of FDTS SAM increases to about 20 A within 2 h, which is close to the molecular chain length of FDTS, and then the thickness in-... 

Fig. 5. Variation in the chain-length distribution in M. citrifolia suspensions during a typical experimental jet run [130]...

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