Dynamic Fragility of α‐Olefin Molecular Bottlebrushes

The glass transition temperature, dynamic fragilities, and flow activation energy of a series of well‐entangled poly(α‐olefin) (PαO) molecular bottlebrushes were measured as a function of side chain length (N_sc ). The PαO bottlebrushes studied here have side chain lengths, N_sc , ranging from 4 (poly(1‐hexene)) to 10 (poly(1‐dodecene). A linear polyolefin (polypropylene), with Nsc = 1, was included in this study as a reference. The observed glassy dynamics behavior in the PαO bottlebrushes is opposite to that observed in linear polymers, namely, the glass transition temperature, the dynamic fragility, and the activation energy of structural relaxation are decreasing functions of the backbone rigidity. This anomalous behavior is due to a decrease in correlation between adjacent backbones, which is directly related to their cooperativity in the α‐relaxation, as N_sc and the concomitant distance between backbones increase. This change in conformation is also manifested as an increase in free volume and the consequent decrease in monomeric friction coefficient. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 1293–1299