Low molecular weight fractions

Oil Content. The production of petroleum waxes involves the removal of oil therefore, the oil content (actually the percentage of oil and low molecular weight fractions) is one indication of the quaUty of the wax. Oil content is deterrnined (ASTM D721) as that percentage of the wax soluble in methyl ethyl ketone at —31.7 C. 

Some skin sensitization to low molecular-weight DGEBPA resins (mol wt - 340) has been shown in animals and humans. Skin sensitization decreases with an increase in molecular weight but the presence of low molecular-weight fractions in the advanced resins may present a hazard to skin sensitization (43). 

Sodium poly(a-L-glutamate). It was washed with acetone, dried, dissolved in water and ppted with isopropanol at 5°. Impurities and low molecular weight fractions were removed by dialysis of the aqueous solution for 50h, followed by ultrafiltration through a filter impermeable to polymers of molecular weights greater the 10. The polymer was recovered by freeze-drying. [Mori et al. J Chem Soc, Faraday Trans I 2583 1978.]... 

Low molecular weight fractions can be detected by smelling the inside of almost any freshly made polyethylene container. The amount varies with the specific polyethylene resin and the type of processing that have been used. 

In the low molecular weight fraction a relatively high content of the 3,4-linkages is formed, characteristic of the polymers produced in the presence of TMEDA. On this basis it was concluded that the unassociated polymers coordinated with TMEDA propagate more slowly than those unassociated and non-coordinated with the diamine, a conclusion concordant with the previously discussed findings of Fontanille84) and confirmed by Schue, 55> for lithium polyisoprene. 

Figure 4. Chromatogram on HW-40 S column of the low molecular weight fraction (Fraction 3) from the HW-55 S column chromatography of the EPG-digested alkali extract.

Figure 9 shows the result of injecting 10 gA of the total low molecular weight fraction from GPC 1 (Column Code A2) into GPC 2 (Column Code Bl). With this column code, GPC 2 is performing as a High Performance Liquid Chromatograph (HPLC). Separation is based upon solubility (i.e. composition differences) rather than upon molecular size. Methyl methacrylate monomer was used as a reference and added to the solution injected into GPC 1. Concentrations of n-butyl methacrylate, styrene and conversion are readily calculated from the peak areas and initial concentrations. 

Effect of Low Molecular Weight Fraction on Fibre Strength... 

Table 2 Results of the calculated effect of the low molecular weight fraction on the ultimate fibre strength for the three PpPTA polymer samples listed in Table 1. The constants used in the calculation are ec=240,g=2, t0=0.4 GPa and u0= 1.3 nm.The maximum ultimate strength for infinite long chains using these constants is 5 GPa... 

When 3(4)-substituted thiophenes (e.g., 3-hexylthiophene) are used as monomers, the polymers are partly or completely soluble in low polar organic solvents like toluene, chloroform, dichloromethane, THF. Therefore, after washing with ethanol, the polymer is dried, then dissolved in chloroform and reprecipitated into methanol or acetone to remove low-molecular-weight fractions. The solid is collected by filtration, washed with methanol, and dried in vacuo. 

Polymerizations often afford polymodal product molecular weight distributions,18 with typically a low molecular weight fraction of several hundred daltons (fraction I), an intermediate fraction of about 4,000 (fraction II) and then a high molecular weight fraction of 10s or 106 (fraction III), though the relative proportions of the fractions depend... 

Fig. 2.2 Comparative chromatographic profiles of low molecular weight fraction isolated from rat brain...

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