Effect of Chain Length

Although it is thought that translation of a polymer ehain proeeeds by means of a series of segmental jumps involving short kinetic units, which may each consist of 15 to 30 chain atoms, the complete movement of a ehain eannot remain unalfeeted by the surrounding chains. As stated previously, eonsiderable entangjranrait exists in the melt, and any motion will be retarded by other ehains. 

FIGURE 13.7 Dependence of melt viscosity on chain length for polyisobutylene fractions measured at low shear rates and at 490 K. (Data by Fox, T.G. and Flory, RJ., J. Phys. Chem. 

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S. K. Kumar, M. Vacatello, D. Y. Yoon. Off-lattice Monte Carlo simulations of polymer melts confined between two plates. 2. Effects of chain length and plate separation. Macromolecules 25 2189-2197, 1990. 

Treatments (Smith-Ewart,79 pseudo-bulk77) have been devised which allow for the possibility of greater than one radical per particle and for the effects of chain length dependent termination. Further discussion on these is provided in the references mentioned above.77 751... 

Some of the issues associated with RAFT emulsion polymerization have been attributed to an effect of chain length-dependent termination.528 In conventional emulsion polymerization, most termination is between a long radical and a short radical. For RAFT polymerization at low conversion most chains are short thus the rate of termination is enhanced. Conversely, at high conversion most chains are long and the rate of termination is reduced. 

FIG. 8 Effect of chain length on the CMC concentration at 35°C [86]. (Reprinted with permission of American Oil Chemists Society.)... 

The effect of chain length on the pseudo rate constant is shown in Fig. 18. Clearly, the optimum chain length for AOS is 16 carbon atoms. However, at this optimum the rate of oil solubilization for AOS is still below that observed for the reference compound DOBS 103, a sodium alkylbenzenesulfonate with 10-13 carbon atoms in the alkyl chain. Increasing the chain length of IOS subjected to an aging step before hydrolysis with NaOH (IOSa in Fig. 18) leads to a continuously increasing rate of oil solubilization. The highest rate was... 

FIG. 18 The effect of chain length on the pseudo rate constants (Km (100 90)) of n-hexadecane solubilization by olefinsulfonates/dobanol 45-3 solutions at 40°C. AOS, a-olefinsulfonate IOS a, aged I-olefinsulfonate IOS d, directly hydrolyzed I-olefin-sulfonate. 

FIG. 8 Effect of chain length of a-ester sulfonates and water hardness on detergency R for fabrics soiled with clay/sebum (T = 60°C 1 g/L surfactant). (From Ref. 58.)... 

Wu, C.W., Sanborn, T.J., Zuckermann, R.N., and Barron, A. E. Peptoid oligomers with alpha-chiral, aromatic side chains Effects of chain length on secondary structure. /. Am. Chem. Soc. 2001, 723, 2958-2963. 

A few complexes are known with substituents in the y- or S-positions, which allow one to see the effect of chain length. Of the DMG complexes... 

Effects of chain length and substitution. Comparing the stabiiity of alkyl nitrates or aliphatic nitrated derivatives, in spite of instability to the extent of making it hazardous to handle them, stability increases rapidly with the number of alkyl groups. So nitroethanes, especially nitropropanes and nitrobutanes, are commonly used industrial raw materials. 

Strain-induced crystallization would presumably further improve the ultimate properties of a bimodal network. It would therefore obviously be of considerable importance to study the effect of chain length distribution on the ultimate properties of bimodal networks prepared from chains having melting points well above the very low value characteristic of PDMS. Studies of this type are being carried out on bimodal networks of polyethylene oxide) (55), poly(caprolactone) (55), and polyisobutylene (56). 

J. Rontani, C. Aubert, Trimethylsilyl transfer during electron ionization mass spectral fragmen tation of some or hydroxycarboxylic and to dicarboxylic acid trimethylsilyl derivatives and the effect of chain length, Rapid Commun. Mass Spectrom., 18, 1889 1895 (2004). 

Effects of chain length on cyclization. The effect of chain length on cyclization of a series of acyclic precursors of benzo-crowns, of which (168) is the first member, has been studied (Mattice Newkome, 1982). In accordance with kinetic data, calculations of the Monte Carlo type indicate that the probability of adoption of a conformation with a small head-to-tail distance makes a significant contribution to the cyclization rate for the small to medium rings. 

The effect of chain length on the ability of degraded amylose to form complexes was studied by Whistler and associates.63 When amylose is hydrolyzed to a degree of polymerization of 20 to 40, it no longer forms insoluble complexes with nitrobenzene, n-pentyl acetate and 2-heptanone, although it still does with 1-butanol and 2-nitropropane. 

In order to investigate the effect of chain length of alkenes upon acidity and aggregation, Thiele and Streitwieser probed the equilibrium acidity of a series of polyenes using UV VIS-spectroscopy in THF at 25 °C Ph(CH=CH) CH2Ph (n = 1, DP3 n = 2, DP5 n = 3, DP7 n = 4, DP9)70. The equilibrium acidity was determined using the transmetallation reaction of equation 3 with Cs+ as the counterion. The results were consistent with... 

Me2N(CH2)mNMe2 (Fig. 16) and that for the formation of N-tosylaza-cycloalkanes [9] (Fig. 10). We have also pointed out (p. 49) that the effect of chain length on the ease of closure of [11] by intramolecular acylation of the... 

Influence of subphase temperature, pH, and molecular structure of the lipids on their phase behavior can easily be studied by means of this method. The effect of chain length and structure of polymerizable and natural lecithins is illustrated in Figure 5. At 30°C distearoyllecithin is still fully in the condensed state (33), whereas butadiene lecithin (4), which carries the same numEer of C-atoms per alkyl chain, is already completely in the expanded state (34). Although diacetylene lecithin (6) bears 26 C-atoms per chain, it forms both an expanded and a condensed phase at 30°C. The reason for these marked differences is the disturbance of the packing of the hydrophobic side chains by the double and triple bonds of the polymerizable lipids. At 2°C, however, all three lecithins are in the condensed state. Chapman (27) reports about the surface pressure area isotherms of two homologs of (6) containing 23 and 25 C-atoms per chain. These compounds exhibit expanded phases even at subphase temperatures as low as 7°C. 

Table 12.2. Effect of chain length of ligand bridge on rate and M,i [9]a...

The first systematic study of the metabolic hydrolysis of primary aliphatic amides was carried out by Bray et al. in 1950 [1]. The substrates were incubated in rabbit liver preparations for 5 h at 37°. In Fig. 4.2, the effect of chain length on the degree of hydrolysis of amides containing 1 to 18 C-atoms (4.1) is shown. The extent of hydrolysis was very small for the first three homo-... 

Fig. 4.2. The effect of chain length (li) on the degree of hydrolysis [%] of primary amides by rat liver preparations (5 h at pH 7.4). Black bars amides of normal saturated fatty acids hatched bar isohexanamide unshaded bars amides of m-phenyl-substituted saturated fatty...

Cyclic olefins and diolefins form much more aerosol than 1-alkenes that have the same number of carbon atoms (for example, cyclohexene 1-hexene, and 1,7-octadiene 1-octene). The same effect of chain length and double-bond position is observed for diolefins (1,7-octadiene > 1,6-heptadiene > 1,5-hexadiene, and 1,7-octadiene 2,6-octadiene). Heavier unsaturated cyclic compounds, such as indene and terpenes, form even more aerosol. 

RESIDUAL SULFONATE CONCENTRATION, kmol/m Figure 4. Effect of chain length. 

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