Molecular weight from dispersion measurements

Elemental analyses were performed by Galbraith Laboratories, Inc., of Knoxville, TN. The compositions of the HS-MOTSS copolymers were derived from the average of the values calculated from the reported halogen and silicon content. The molecular weight and dispersity of the polymers were measured in tetrahydrofuran by size... 

The solute molecular weight enters the van t Hoff equation as the factor of proportionality between the number of solute particles that the osmotic pressure counts and the mass of solute which is known from the preparation of the solution. The molecular weight that is obtained from measurements on poly disperse systems is a number average quantity. 

Katz and Scott [1] measured the diffusivity of 69 different solutes having molecular weights ranging from 78 to 446. The technique they employed was to measure the dispersion of a given solute band during passage through an open tube. 

Low molecular weight solids were dispersed in KBr pellets polymer films were cast from CHCI3. Intrinsic viscosities were measured by standard procedures using a Cannon Ubbelohde dilution viscometer. 

Polarizability is a measure of the ease with which the electrons of a molecule are distorted. It is the basis for evaluating the nonspecific attraction forces (London dispersion forces) that arise when two molecules approach each other. Each molecule distorts the electron cloud of the other and thereby induces an instantaneous dipole. The induced dipoles then attract each other. Dispersion forces are weak and are most important for the nonpolar solvents where other solvation forces are absent. They do, nevertheless, become stronger the larger the electron cloud, and they may also become important for some of the higher-molecular-weight polar solvents. Large solute particles such as iodide ion interact by this mechanism more strongly than do small ones such as fluoride ion. Furthermore, solvent polarizability may influence rates of certain types of reactions because transition states may be of different polarizability from reactants and so be differently solvated. 

Fig. 11 Nascent radiation initiated PTFE dispersion particles. The polymerization conditions were (a) 0% emulsifier, 90 min, (b) 0.5% emulsifier, 60 min, (c) 1% emulsifier, 60 min, (d) 2% emulsifier, 90 min, all for essentially the same radiation dose rate at 25 °C in water (with 1.3% hexadecane and ammonium perfluorooctanoate emulsifier) at 30-kg/cm2 pressure. The measured molecular weights, the corresponding extended chain lengths (eel) the and dimensional characteristics are, respectively, (a) Mn = 230 x 104, edn = 6.0 pm, particle volume approximately 7 x 108 Da (b) Mn = 50 x 104, eel = 1.3 pm, rod diameter approximately 100 molecules (c) Mn = 20 x 104, ed = 0.52 pm rod length (d) Mn=2xl04, ed = 520A. (Reprinted from Ref. [14] with permission from Wiley-Interscience)...

In Tung s experiments, aqueous solutions of calf thymus DNA from commercial sources with average molecular weights in the range 106 to 107 were measured from 10 Hz to several kHz with or without added salts (NaCl and BaCl.) Some of the results are shown in Figure 1. In Figure l(a)f dispersions of e (real part of e ) at 5, 15, and 25C extrapolated to zero frequency show that the static permittivities increase with increasing temperature, which is contrary to the l/T dependence expected for permanent dipole polarization, as in eq 7, but can be explained as a consequence of polyion polarization. 

Primary Mode of Reaction and Consequences (9). Bovine a8i-casein (Variant B) was prepared from fresh milk (12) and immediately succinylated to increase water dispersibility (13). This succinylated asi-casein preparation, molecular weight of ca. 25,000 daltons, was used as the hydrophilic protein substrate. The compound L-norleucine 1-13C-dodecyl ester, prepared from K13CN and 1-bromoundecane through four steps (14,15,16), was used as the lipophilic nucleophile. C-13 NMR measurements showed that this sample gave only one signal at a distance of 65.2 ppm from the signal of tetramethylsilane (TMS). 

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