Small-Angle Neutron Scattering Analysis of Bottlebrush Polymers made by Grafting-Through Polymerization

Published

August 22, 2013

Author(s)

Stacy L. Pesek, Xianyu Li, Boualem Hammouda, Kunlun Hong, Rafael Verduzco

Abstract

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.

Citation

Macromolecules

Volume

46

Pub Type

Journals

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Keywords

Bottlebrush, molecular brush, polymer, SANS, conformation, solution properties, grafting-through, polystyrene, branched

Citation

Pesek, S. , Li, X. , Hammouda, B. , Hong, K. and Verduzco, R. (2013), 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 September 19, 2024)