Reimer Holm

Rapid determination of molecular parameters of synthetic polymers by precipitation/redissolution high-performance liquid chromatography using “molded” monolithic column

Rapid high-performance liquid chromatography (HPLC) of polystyrenes, poly(methyl methacrylates), poly(vinyl acetates), and polybutadienes using a monolithic 50 × 4.6 mm i.d. poly(styrene-co-divinylbenzene) column have been carried out. The separation process involves precipitation of the macromolecules on the macroporous monolithic column followed by progressive elution utilizing a gradient of the mobile phase. Depending on the character of the separated polymer, solvent gradients were composed of a poor solvent such as water, methanol, or hexane and increasing amounts of a good solvent such as THF or dichloromethane. Monolithic columns are ideally suited for this technique because convection through the large pores of the monolith enhances the mass transport of large polymer molecules and accelerates the separation process. Separation conditions including the selection of a specific pair of solvent and precipitant, flow rate, and gradient steepness were optimized for the rapid HPLC separations of various polymers that differed broadly in their molecular weights. Excellent separations were obtained demonstrating that the precipitation-redissolution technique is a suitable alternative to size-exclusion chromatography (SEC). The molecular weight parameters calculated from the HPLC data match well those obtained by SEC. However, compared to SEC, the determination of molecular parameters using gradient elution could be achieved at comparable flow rates in a much shorter period of time, typically in about 1 min.

Microanalysis of Polymers with Special Emphasis on Surface Characterization

When small amounts of a substance are enriched in small volumes or in monolayers at the surface of a solid body, th0065y can be directly detected by instrumental analysis methods without any chemical separation. In the polymer field surface analysis with methods like ESCA, AES, SIMS, and ISS is still in its infancy. Examples of application are the investigation of surface changes, such as the effects of weathering, etching and corona treatments, and the detection of surface deposits consisting of materials like antistatic agents, lubricants, and exuded constituents. Because of their high surface sensitivity and ability to differentiate between surface and bulk phenomena, surface analysis methods are particularly suitable for the investigation of interfaces between polymers and metals, e.g. in radial tires or cable insulations. It is pointed out that in these cases the inadequacies of the preparation methods limit the value of the analytical findings more than the inadequacies of the analysis methods.