Comparison of the Mayo and chain length distribution procedures for the measurement of chain transfer constants

The Mayo and chain length distribution (CLD) procedures for the measurement of chain transfer constants are outlined and compared, and it is found tha t both procedures are essentially equivalent and yield reliable results. It is shown that both procedures are relatively insensitive to changes in ini tiator concentration under practical circumstances and that the most reliab le results are obtained with the Mayo procedure using the weight-average mo lecular weight and with the CLD procedure using the slope in the ln(number distribution) at the peak molecular weight. The CLD procedure is discussed in more detail, and it is shown that as long as termination is not a signif icant chain stopping event, the ln(number distribution) should be a straigh t line. Therefore, the limiting slope of such a plot can be reliably obtain ed, preferably from the peak molecular weight region, as previously discuss ed by Mead and Mead [Macromolecules 1996, 29, 7727]. However, when terminat ion is significant, the limiting slope is only reached at high molecular we ights, and it is unlikely that such slopes can be reliably obtained from ex periments.