High molecular weight polystyrene analysis

Small particle size resins provide higher resolution, as demonstrated in Fig. 4.41. Low molecular weight polystyrene standards are better separated on a GIOOOHxl column packed with 5 /u,m resin than a GlOOOHg column packed with 10 /Ltm resin when compared in the same analysis time. Therefore, smaller particle size resins generally attain a better required resolution in a shorter time. In this context, SuperH columns are best, and Hhr and Hxl columns are second best. Most analyses have been carried out on these three series of H type columns. However, the performance of columns packed with smaller particle size resins is susceptible to some experimental conditions such as the sample concentration of solution, injection volume, and detector cell volume. They must be kept as low as possible to obtain the maximum resolution. Chain scissions of polymer molecules are also easier to occur in columns packed with smaller particle size resins. The flow rate should be kept low in order to prevent this problem, particularly in the analyses of high molecular weight polymers. 

It should be noted that a TL, l would not be expected in this polystyrene) braid sample because of its high molecular weight (approximately 100,000) (46). Also, this analysis of the composite structure of the braid supports Nielsen s (47) suggestion that rL, L arises solely from the residual elasticity of the glass. The torsional pendulum, braid, and TL, l will be discussed in more detail elsewhere (16,17). 

For the analysis of organic-soluble and water-soluble synthetic polymers, silica-based packing materials have not become as widely used as was originally envisioned (8). Major improvements in the properties of polymer-based supports have contributed to their increased use in GPC. Columns packed with polystyrene divinylbenzene particles are now as efficient as those filled with silica particles of the same size. Because polymer-based packings can be synthesized with very small (<60 A) and very large (>4000 A) pores, they provide better selectivity than silica columns for the separation of monomers, as well as for very high molecular weight (5-20 million dalton) polymers. 

A recent study of polystyrene over an extended temperature range has indicated that a helix-coil transition can be observed in certain high molecular weight samples at approximately 333 K. It has also been reported that crystals of polystyrene grown above 333 K have a different structure, as revealed by X-ray analysis, compared with those formed below this temperature. 

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