Polymers, periodic polyethylene results

The final step in the process of standardizing our columns was to try and maintain the high quality of columns from batch to batch of gel from the manufacturer. This was done by following the basic procedures outlined earlier for the initial column evaluation with two exceptions. First, we did not continue to use the valley-to-peak ratios or the peak separation parameters. We decided that the D20 values told us enough information. The second modification that we made was to address the issue of discontinuities in the gel pore sizes (18,19). To do this, we selected six different polyethylenes made via five different production processes. These samples are run every time we do an evaluation to look for breaks or discontinuities that might indicate the presence of a gel mismatch. Because the resins were made by several different processes, the presence of a discontinuity in several of these samples would be a strong indication of a problem. Table 21.5 shows the results for several column evaluations that have been performed on different batches of gel over a 10-year period. Table 21.5 shows how the columns made by Polymer Laboratories have improved continuously over this time period. Figure 21.2 shows an example of a discontinuity that was identified in one particular evaluation. These were not accepted and the manufacturer quickly fixed the problem. 

Direct evidence of nucleation during the induction period will also solve a recent argument within the field of polymer science as to whether the mechanism of the induction of polymers is related to the nucleation process or to the phase separation process (including spinodal decomposition). The latter was proposed by Imai et al. based on SAXS observation of so-called cold crystallization from the quenched glass (amorphous state) of polyethylene terephthalate) (PET) [19]. They supposed that the latter mechanism could be expanded to the usual melt crystallization, but there is no experimental support for the supposition. Our results will confirm that the nucleation mechanism is correct, in the case of melt crystallization. 

For some years a wide range of labware (e.g., flasks, vessels, Erlenmeyer flasks, syringes, separation funnels or even complete distillation apparatus) made of fluoropolymers (Table 4) has been commercially available and can be almost universally utilized over a temperature range of — 270 to + 260 C. Polyethylene and polypropylene can both be used for short periods, however, hydrogen fluoride can remove plasticizers from these polymers resulting in brittleness and also adversely affecting fluorinations. 

In another part of this study we wished to see the effects of post-modification treatments on the properties of the modified LDPE surface. Polyethylene samples were photosulfonated for different periods of time. Afterwards they were subjected to an after-treatment by conditioning in an electrolyte solution (aqueous KC1, 10-3 M) for 48 hours and then characterized by zeta potential measurements. This conditioning process resulted in a shift of f to even less negative values (see Fig. 8). This finding may be explained by the swelling of the polymer samples (water adsorption) in water that causes a shift of the shear plane of the electrochemical double layer into the liquid phase. This effect demonstrates that storage conditions and pre-conditioning may exert a pronounced influence on the zeta potential recorded for surface-modified polymers. Phenomena of this kind have already been described in previous literature [26,27],... 

Tobolsky and Takahashi (7,8) showed that large concentrations of S8 can remain dissolved in a liquid condition in other polymers. In many cases these compositions appear completely stable, i.e., there is no tendency for the dissolved sulfur to crystallize out. The best example is cross-linked polyethylene tetrasulfide polymers which can retain 40% of dissolved sulfur in the form of liquid S8 over long periods of time. The sulfur was shown to be S8 by quantitatively extracting it with carbon disulfide. It was demonstrated that the specific volume of the dissolved sulfur plotted against temperature fits smoothly with the data of specific volume of molten sulfur vs. temperature and finally that the mechanical properties of the cross-linked polymers containing dissolved sulfur are just what would be expected from plasticized, cross-linked, amorphous polymers. Ellis (9) reported the use of resins made by the interaction of 2,3-xylenol and sulfur monochloride as sulfur additives. These resins were added to three times their weight of molten sulfur. There was no indication of sulfur crystallization in the resultant material, which also... 

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