Comb Polymers with Triazole Linkages under Thermal and Mechanical Stress

Abstract

Assessing the stability of molecular bonds in polymer architectures is of critical importance for determining conditions for extrusion, molding, and processing. The topological complexity of branched polymers defines their strain hardening and consequently their melt strength properties, critical parameters for their exploitation in applications. Their molecular architecture is defined by the grafting density and the chain length of the backbone as well as branches. Herein, we introduce a set of polymer combs to establish an understanding of the above parameters on the stability of the popular triazole linkage—often exploited in tethering the branches to the backbone—during thermal treatment and shearing. We exploit a combination of reversible deactivation radical polymerization (RDRP) and copper-catalyzed alkyne–azide cycloaddition (CuAAC) to construct comb polymers (ranging in backbone number-average molecular weight from 39.9 to 55.6 kg mol–1 and a branch length from 3.3 to 18 kg mol–1) with statistically located branches tethered via triazole-based ligation to the backbone. These polymer combs were subsequently thermally challenged at 150 °C (or 180 °C) in an inert atmosphere as well as subjected to shearing at the same temperature. The resulting molecular cleavage processes were analyzed via size exclusion chromatography (SEC) as well as SEC coupled to high-resolution electrospray ionization mass spectrometry (SEC-HR ESI MS) to establish a mechanistic image of branch debonding when it occurs. In addition, by virtue of this approach, we establish an in-depth understanding of how the comb architecture dictates its stability under otherwise unchanged chemical bonding conditions via triazole units, allowing to adopt design criteria for generating thermally and mechanically stable comb structures.