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 that both procedures are essentially equivalent and yield reliable results. It is shown that both procedures are relatively insensitive to changes in initiator concentration under practical circumstances and that the most reliable results are obtained with the Mayo procedure using the weight-average molecular 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 significant chain stopping event, the ln(number distribution) should be a straight line. Therefore, the limiting slope of such a plot can be reliably obtained, preferably from the peak molecular weight region, as previously discussed by Mead and Mead [Macromolecules 1996, 29, 7727]. However, when termination is significant, the limiting slope is only reached at high molecular weights, and it is unlikely that such slopes can be reliably obtained from experiments.