Polymerization kinetics : monitoring monomer conversion using an internal standard and the Key Role of sample t0

The use of an internal standard is a conventional and convenient way to monitor the conversion of one or several monomers during a controlled radical polymerization. However, the validity of this technique relies on an accurate determination of the initial monomer-tointernal standard ratio, A0, because all subsequent calculations of the conversion are based on this value. In most kinetic studies using an internal standard for the determination of the conversion, an incorrect determination of the value of A0 will result in absurd conclusions and will thus be detected and corrected. However, an incorrect determination of A0 can be significantly misleading in the case of controlled polymerization. This article shows that deviation of the kinetic plots from their true shape because of an error in A0 will not look absurd in the case of controlled polymerization. On the contrary, the plots will fit with a possible deviation of the polymerization from a "quasi-living" to a less controlled process. As a consequence, an error on A0 may not be detected and can result in a misinterpretation of the behavior of the system.