The Influence of a Potential Diffusion Control on the Outcome of Modular Polymer–Polymer Click Conjugations

Abstract

AbstractThe only reliable factors for assessing if a polymer–polymer click conjugation is successful are an assessment of the number average $\overline {M} _{{\rm n}} $ of the resulting molecular weight distribution (MWD) and the shape of the number, respectively, concentration distribution as was demonstrated earlier. The present contribution explores if a potential chain length dependence (CLD) of the conjugation reaction—caused by a potential diffusion control—can affect the outcome of the polymer–polymer click ligation process. The CLD of the click rate coefficient, $k_{{\rm click}}^{{\rm i},{\rm j}} $, was implemented via a geometric mean approximation for chain length dependent termination, employing α‐values from 1.0 to 0.2. The number averages $\overline {M} _{{\rm n}} $ and weight averages $\overline {M} _{{\rm w}} $ (and thus the PDIs) of the initial distributions were varied widely to explore under which conditions CLD effects have the largest impact. The present study clearly demonstrates that—if diffusion effects and thus a CLD of $k_{{\rm click}}^{{\rm i},{\rm j}} $—play a role in polymer–polymer ligation, the MWDs generated through conjugation display a marked conversion dependence, i.e., $M_{{\rm n}}^{{\rm click}} (x)$, with the maximum $M_{{\rm n}}^{{\rm click}} $ being reached at quantitative conversions. While the $\overline {M} _{{\rm n}} $ reached at quantitative conversions coincides with the $\overline {M} _{{\rm n}} $ obtained under CL‐independent conditions, the final $\overline {M} _{{\rm w}} $ of both the CLD and non‐CLD differs significantly. While the present theoretical study cannot replace the actual experiment, it unambiguously demonstrates that polymer–polymer click conjugations can be influenced by CLD effects. Given the larger α‐values for smaller chain length, broad distributions in the range up to approximately 3 000 Da are especially affected.magnified image