On the Quantitative Click Conjugation of Molecular Weight Distributions: What Can Theoretically Be Expected?

The assessment of the success of a click conjugation for block copolymer formation often occurs via ill-defined criteria based on the qualitative shape of the size exclusion chromatography (SEC) distribution as well as unsuitable characteristics of these molecular weight distributions such as the peak molecular weight, M(p). The data presented herein illustrate that from the shape of the SEC distribution, w(log M) versus log M, of the click product - under the assumption of a 100% efficient conjugation reaction - a conclusion about the effectiveness of the click conjugation cannot be derived. It is demonstrated that under certain conditions multi-modal molecular weight distributions are obtained from two well-defined monomodal initial distributions. Similarly, the comparison of peak maxima between the conjugate and the initial SEC distributions is a poorly defined criterion to assess the success of a conjugation. The only reliable assessment for the success of the click coupling reaction is the true number average molecular weight, (M) over bar (n), of the SEC distribution of the click product, as well as a plot of the concentration or number distributions, c versus M, of the precursors and product polymer.