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(m ethyl methacrylates), poly(vinyl acetates), and polybutadienes using a mono lithic 50 x 4.6 mm i.d. poly(styrene-co-divinylbenzene) column have been ca rried out. The separation process involves precipitation of the macromolecu les on the macroporous monolithic column followed by progressive elution ut ilizing a gradient of the mobile phase. Depending on the character of the s eparated polymer, solvent gradients were composed of a poor solvent such as water, methanol, or hexane and increasing amounts of a good solvent such a s THF or dichloromethane. Monolithic columns are ideally suited for this te chnique because convection through the large pores of the monolith enhances the mass transport of large polymer molecules and accelerates the separati on process. Separation conditions including the selection of a specific pai r of solvent and precipitant, flow rate, and gradient steepness were optimi zed for the rapid HPLC separations of various polymers that differed broadl y in their molecular weights. Excellent separations were obtained demonstra ting that the precipitation-redissolution technique is a suitable alternati ve to size-exclusion chromatography (SEC). The molecular weight parameters calculated from the HPLC data match well those obtained by SEC. However, co mpared to SEC, the determination of molecular parameters using gradient elu tion could be achieved at comparable flow rates in a much shorter period of time, typically in about 1 min. (C) 2000 John Wiley & Sons, Inc.