title: Metalated diblock and triblock poly(ethylene oxide)-block-poly(4-vinylpyridine) copolymers: understanding of micelle and bulk structure.
abstract: The paper provides new insights into the structure of Pt-containing diblock and triblock copolymers based on poly(ethylene oxide) (PEO) and poly(4-vinylpyridine) (P4VP), using a combination of atomic force microscopy (AFM), X-ray diffraction (XRD), transmission electron microscopy (TEM), and anomalous small-angle X-ray scattering (ASAXS). Parallel studies using methods contributing supplemental structural information allowed us to comprehensively characterize sophisticated polymer systems during metalation and to exclude possible ambiguity of the data interpretation of each of the methods. AFM and TEM make available the determination of sizes of the micelles and of the Pt-containing micelle cores, respectively, while a combination of XRD, TEM, and ASAXS reveals Pt-nanoparticle size distributions and locations along with the structural information about the polymer matrix. In addition, for the first time, ASAXS revealed the organization of Pt-nanoparticle-filled diblock and triblock copolymers in the bulk. The nanoparticle characteristics are mainly determined by the type of block copolymer system in which they are found: larger particles (2.0-3.0 nm) are formed in triblock copolymer micelles, while smaller ones (1.5-2.5 nm) are found in diblock copolymer micelles. This can be explained by facilitated intermicellar exchange in triblock copolymer systems. For both systems, Pt nanoparticles have narrow particle size distributions as a result of a strong interaction between the nanoparticle surface and the P4VP units inside the micelle cores. The pH of the medium mainly influences the particle location rather than the particle size. A structural model of Pt-nanoparticle clustering in the diblock PEO-b-P4VP and triblock P4VP-b-PEO-b-P4VP copolymers in the bulk was constructed ab initio from the ASAXS data. This model reveals that nearly spherical micellar cores of about 10 nm in diameter (filled with Pt nanoparticles) aggregate forming slightly oblate hollow bodies with an outer diameter of about 40 nm.
authors.affiliation: Department of Chemistry, Indiana University, 800 East Kirkwood Avenue, Bloomington, Indiana 47405, USA. lybronst@indiana.edu
authors.forename: Lyudmila M
authors.initials: LM
authors.lastname: Bronstein
authors.forename: Stanislav N
authors.initials: SN
authors.lastname: Sidorov
authors.forename: Vasilii
authors.initials: V
authors.lastname: Zhirov
authors.forename: Denis
authors.initials: D
authors.lastname: Zhirov
authors.forename: Yuri A
authors.initials: YA
authors.lastname: Kabachii
authors.forename: Sergey Y
authors.initials: SY
authors.lastname: Kochev
authors.forename: Peter M
authors.initials: PM
authors.lastname: Valetsky
authors.forename: Barry
authors.initials: B
authors.lastname: Stein
authors.forename: Olga I
authors.initials: OI
authors.lastname: Kiseleva
authors.forename: Sergey N
authors.initials: SN
authors.lastname: Polyakov
authors.forename: Eleonora V
authors.initials: EV
authors.lastname: Shtykova
authors.forename: Elena V
authors.initials: EV
authors.lastname: Nikulina
authors.forename: Dmitri I
authors.initials: DI
authors.lastname: Svergun
authors.forename: Alexei R
authors.initials: AR
authors.lastname: Khokhlov
mesh_terms: D008823:Micelles; D046529:Microscopy, Electron, Transmission / Q000379:methods; D008958:Models, Molecular; D015394:Molecular Structure; D053758:Nanoparticles / Q000737:chemistry*; D009944:Organoplatinum Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D010316:Particle Size; D011092:Polyethylene Glycols / Q000737:chemistry*; D011108:Polymers / Q000737:chemistry*; D053838:Scattering, Small Angle; D014753:Vinyl Compounds / Q000737:chemistry*; D014961:X-Ray Diffraction
chemical_list: D008823:Micelles; D009944:Organoplatinum Compounds; D011108:Polymers; D014753:Vinyl Compounds; C520176:poly(4-vinylpyridine)-block-poly(ethylene oxide); D011092:Polyethylene Glycols