Small-angle neutron scattering analysis of bottlebrush backbone and side chain flexibility

Bottlebrush polymers have densely tethered side chains grafted to a linear polymer backbone, resulting in stretching of both the side chains and backbone. Prior studies have reported that the side chains are only weakly stretched while the backbone is highly elongated. Here, scaling laws for the bottlebrush backbone and side chains are determined through small-angle neutron scattering analysis of a systematic series of poly(lactic acid) bottlebrush polymers synthesized via a grafting-through ring-opening polymerization. Scattering profiles are modeled with the empirical Guinier-Porod, rigid cylinder, and flexible cylinder models. Side chains are found to be only weakly stretched, with an end-to-end distance proportional to N-0.55, while the overall bottlebrush increases in size proportional to N-0.77. These results demonstrate that the bottlebrush backbone is not fully extended and that both side chains and backbone have significant conformational flexibility in solution. (c) 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017, 55, 104-111