METHYL CYCLOHEXANE AS A NEW ELUTING SOLVENT FOR THE SIZE-EXCLUSION CHROMATOGRAPHY OF POLYETHYLENE AND POLYPROPYLENE AT 90-DEGREES-C

Size-exclusion chromatography using halogenated aromatic solvents such as trichlorobenzene at 145 degrees C is widely used for industrial po lyolefins. Such high temperature operation requires special instrument design and causes many operational problems, In this work, a new elut ing solvent, methyl cyclohexane, has been successfully used at 90 degr ees C for the size-exclusion chromatography of industrial (high-molecu lar-mass) grades of polypropylene and polyethylene. Sample preparation involves dissolution in decalin at temperatures as high as 140 degree s C, followed by dilution in methyl cyclohexane at 90 degrees C previo us to injection into the SEC column running with methyl cyclohexane as the mobile phase. In addition to permitting operation at 90 degrees C , methyl cyclohexane is less toxic than the usual solvents and has a d ifferential refractive index sensitivity advantage as well. It also pr ovides new opportunities for ultraviolet, fluorescence, and infrared d etection for functionalized polyolefins. However, one disadvantage is that polystyrene adsorbs from this solvent on styrene-based packings. Thus, narrow fractions of polyisobutylene (PIB) were used in place of polystyrene for universal calibration. Another disadvantage is that me thyl cyclohexane is more flammable than halogenated aromatic solvents. A quantitative assessment of the new solvent system is in progress. I nitial results are promising and are presented in this paper.