Elution fractionation of crystalline and amorphous polymers

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Abstract
Elution fractionation has been applied to crystalline and amorphous polymers. Variables such as the method of polymer deposition, elution rate, and temperature have been studied. Atactic polystyrene can be fractionated successfully by either selective or nonselective deposition of the polymer onto the sand column support. However, only polymers having a sufficiently high diffusion rate can be fractionated by nonselective deposition methods. Other polymers with low diffusion rates, such as polyethylene, must be selectively deposited by precipitating the high molecular species first. The fractionation, in this case, is done during the deposition step. The reliability of the fractionation has been checked by additional measurements on the fractions with light scattering, osmotic pressure, and sedimentation. Reproducibility was checked by repeated fractionation of the same polymer, by a blend of two polymers with previously determined molecular weight distributions, and by comparison of calculated and observed molecular weight distribution curves. Intergral and differential molecular curves have also been compared to theoretical logarithmic distributions with good agreement. The paper describes some of the limitations of the elution method such as high molecular weight, highly branched polyethylenes. The elution fractionation has been shown to be a reliable method for establishing molecular weight distributions.