Small-Angle Neutron Scattering Analysis of Bottlebrush Polymers made by Grafting-Through Polymerization
Stacy L. Pesek, Xianyu Li, Boualem Hammouda, Kunlun Hong, Rafael Verduzco
Bottlebrush polymers are highly branched polymer macromolecules with potential applications for anti-fouling coatings, rheological modifiers, and drug delivery systems. However, the solution conformation of bottlebrush polymers has been studied in only a limited set of materials made primarily by grafting-from polymerization. Here we present small-angle neutron scattering (SANS) measurements on a series of polystyrene bottlebrush polymers with varying side-chain and backbone lengths in d8-toluene to analyze the size, shape, and conformation. Bottlebrush polymers with 2 - 6 kg mol-10 polystyrene side-chains (degree of polymerization DP = 14 - 54) and polyoxanorbornene backbones (DP = 10 - 264) were synthesized using a ring-opening metathesis polymerization grafting-through synthetic scheme, which guarantees full side-chain attachment. Absolute molecular weights for the side-chains and overall bottlebrush polymers are determined by a combination of static light scattering and 1H NMR measurements. Analysis by Gunier-Porod, rigid cylinder, and flexible cylinder models provided estimates for bottlebrush polymer length, radius, and stiffness. Consistent with prior measurements, bottlebrush polymer cross-sectional area depends primarily on side-chain DP, and the Rg exhibits a power-law dependence with side-chain DP. We also observe a sphere-to-cylinder transition with increasing backbone DP, with the transition occurring at approximately a backbone DP of 120 for the polystyrene bottlebrush polymers studied. This indicates that cylindrical form factors are inappropriate for bottlebrush polymers with short backbone DPs, and a combination of spherical and cylindrical form factor models provide a comprehensive analysis. The maximum molecular dimension for the series studied varies from 25 up to 350 nm. Transmission electron micrographs reveal only spherical particles with sizes ranging from 25-45 nm, suggesting TEM measurements are a poor reflection of solution conformations.
, Li, X.
, Hammouda, B.
, Hong, K.
and Verduzco, R.
Small-Angle Neutron Scattering Analysis of Bottlebrush Polymers made by Grafting-Through Polymerization, Macromolecules, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=914132
(Accessed May 28, 2023)