Clarification of the effects of topological isomers on the mechanical strength of comb polyurethane

We designed and synthesized a topological isomer with comb and linear polyurethanes (PUs), bearing one, two, and three units of oligo(ethylene glycol) (OEG) at the side chain. Surprisingly, comb PUs with OEG side chain lengths of two and three units showed about twice as much stress at the break as those of the corresponding linear isomers. The analysis of rheological and structural parameters revealed that the comb PU in this study was more suitable for maintaining entanglement concerning the side chain length than that of the conventional comb polymer. Since the comb PU showed high zero shear viscosity like the conventional comb polymer, it was found that there is molecular chain friction due to the side chain. Therefore, it is assumed that both the entanglement compatibility and the molecular chain friction resulted in an enhancement of the mechanical strength, which was achieved by the topological isomer.