Sample pretreatment for aggregate-free PVC molecular weight measurement by size-exclusion chromatography

The procedure of aggregate-free poly(vinyl chloride) (PVC) solutions for size-exclusion chromatography (SEC) at room temperature using tetrahydrofuran (THF) as the mobile phase is proposed. PVC was dissolved in 1,2,4-trichlorobenzene (TCB) at 130 or 140 degrees C for 6 h, precipitated in methanol, filtrated, and dried. The pretreated PVC was again dissolved in THF and SEC measurements were performed at room temperature. High molecular weight (MW) PVC required a higher pretreatment temperature of 140 degrees C. The existence of aggregates sometimes could not be observed by a refractive index detector, but a light-scattering detector attached to the SEC columns could detect them clearly. The slope of the relationship between the MW and retention volume at the high MW region was steep compared with that at the other part of the peak and it was also a good indicator of the existence of aggregates. The pretreatment of PVC resulted in the decrease in MW averages, which was attributed to the disappearance of aggregates and not to the degradation of PVC. The pretreatment at 150 degrees C resulted in the degradation of PVC. (C) 1998 John Wiley & Sons, Inc.