Autocatalysis in the Room Temperature Copper(I)-Catalyzed Alkyne-Azide "Click" Cycloaddition of Multivalent Poly(acrylate)s and Poly(isobutylene)s

The concept of self-healing polymers requires fast and efficient cross-linking processes, ideally based on catalytic reactions. We investigate autocatalytic effects in cross-linking processes based on the copper(I)-catalyzed alkyne azide "click" cycloaddition reaction (CuAAC), taking advantage of the 1,3-triazole rings formed during the CuAAC-based cross-linking, which act as ligands for subsequent "click"-reactions in turn accelerating the reaction rate of subsequent CuAAC-reactions. Catalysis during the cross-linking reactions of multivalent polymeric allcynes and azides (nine atactic random poly(propargyl acrylate-co-n-butyl acrylate)s, M-n = 7000-23400 g/mol) prepared via nitroxide mediated polymerization (NMP) and displaying alkyne-contents ranging from 2.7 mol 96 to 14.3 mol 96 per chain were studied via melt-rheology and differential scanning calorimetry (DSC), revealing significant increases of the reaction rate with increasing allcyne-concentrations. A kinetic analysis showed autocatalytic effects (up to a factor of 4.3) now enabling a deeper understanding of the catalysis as well as on the achievement of a "click"-cross-linking concept acting at room temperature. Effects exerted by the molecular weight were investigated by reacting five three-arm-star azido-telechelic poly(isobutylene)s (PIB's) (Mn = 5500-30000 g/mol) and one three-arm-star allcyne-telechelic PIB (M-n = 6300 g/mol) in the cross-linking-reaction, thus linking molecular mobility to changes in CuAAC-reactivity revealing faster network formation with lower molecular weights. The now designable significant autocatalytic effects together with the optimized reaction rate via the lowest molecular weight compounds enabled the design of a new, highly efficient and fast cross-linking system acting at room temperature.