The progression of intramolecular organizations within a series of dilute poly(amido amine) (PAMAM) dendrimer/methanol solutions is examined by use of small-angle X-ray scattering (SAXS) combined with comparisons to electron density models and radial density distributions extracted by the indirect transformation for the calculation of P(r) (ITP) method. The SAXS from generation 3 (G3) dendrimers are shown to possess scattering features similar to those of star molecules. This contrasts with the SAXS of the much larger G9 and G10 dendrimers. The G10 SAXS exhibits at least Eve resolvable secondary maxima. Those features are successfully reproduced for a model consisting of constant-density spheres with a small amount of polydispersity in molecular size. Scattering from the intermediately sized G4 through G8 dendrimers reflects a consistent evolution of internal structure progressing from "starlike" to "hard-sphere-like" organizations.

Solutions of the poly(propylene imine) dendrimers DAB-dendr-(PA)(32) and DAB-dendr-(PA)(64) in methanol are investigated with small angle neutron scattering over the range of dendrimer mass fraction 0.01 less than or equal to x less than or equal to 0.80. The single particle scattering function, P(q), is used to calculate the structure factor, S(q) of the dendrimer solutions and to evaluate the radius of gyration of the dendrimers in dilute solution giving R-g(+)(DAB-dendr-(PA)(32)) = 12.4 +/- 0.2 Angstrom and R-g(+)(DAB-dendr-(PA)(64)) = (15.6 +/- 0.2) Angstrom. In each case the segment density in dilute solution is 0.35 +/- 0.03 g cm(-3), leaving a large fraction of the dendrimer volume accessible to solvent. We define the "dilute solution regime" for dendrimers to extend to a concentration where the swollen dendrimer volume fraction first equals the value 0.64, which comes at a dendrimer weight fraction of x = 0.25. At this concentration, the spatial arrangement of the dendrimers can be described as a random close packing. For higher concentrations, the experimental scattering functions appear to be self-similar up to a mass fraction of x approximate to 0.60. These observations are consistent with a model of concentrated dendrimer solutions which assumes that individual dendrimers collapse to maintain a volume fraction phi approximate to 0.64, which is the volume fraction of random close packing of hard spheres. Preliminary small X-ray scattering data give further evidence of the dendrimer collapse.

The nature of the structural ordering within semicrystalline poly(3-dodecylthiophene) films has been analyzed using a Warren-Averbach Line-shape analysis which includes up to five orders of the (h00) lattice reflections. This analysis yields a semiquantitative measure of the volume averaged crystallite sizes, the lattice parameter variations, and the disorder fluctuations. The progression of these quantities has been followed through a liquid crystal polymer (LCP) phase transition which occurs in the vicinity of 60 degrees C. The pronounced peak width narrowing of the low-order (h00) reflections, observed on heating, is found to be essentially uncorrelated with a theorized annealing-induced increase in average crystallite size. The major contribution to this narrowing arises from systematic variations in the microscopic heterogeneities and fluctuations. Moreover, Re observe an anomalously large increase in the higher-order (h00) (h = 3-5) peak widths at temperatures spanning that of the thermotropic LCP transition. This effect is found to be strongly correlated with a maximum in the disorder fluctuations, and this relationship suggests an underlying mechanism for the nature of the LCP transition.

The kinetics of the disorder-to-order transition in a polystyrene-bloch-polyisoprene copolymer was studied after it was thermally quenched from the disordered state to the ordered state. The ordered state consists of cylinders arranged on a hexagonal lattice. This state has liquid crystalline symmetry with liquidlike disorder along the cylinders axis and crystalline order in the hexagonal plane. We monitor the kinetics of microstructure formation in the liquid and crystalline directions by a combination of time-resolved depolarized light scattering and small-angle X-ray scattering experiments. At small quench depths, microstructure formation along the liquid and crystalline directions is strongly correlated during all stages of the disorder-to-order transition. We demonstrate that this is expected when microstructure formation occurs by classical nucleation and growth. At large quench depths, however, microstructure formation along the liquid and crystalline directions is not correlated. The growth of crystalline order occurs before the development of a coherent structure along the liquid direction. We argue that this may be a signature of spinodal decomposition in liquid crystals.

This report gives an overview about the first results of an investigation of mixtures that consist of dendrimers and conventional polymers. Poly(amido amine) (PAMAM) or poly(propylene amine) (PPI) dendrimers were blended with linear polymers that contain small amounts of strongly interacting comonomers to enhance the miscibility. Hydrophobically modified dendrimers were incorporated into the miscible polymer blend PS/PVME. Interpenetrating polymer networks (IPNs) were prepared by dispersing the dendrimers in hydroxyethylmethacrylate and polymerizing the vinyl monomer using free radical methods. Small angle neutron (SANS) scattering and small angle x-ray scattering (SAXS) experimets were performed, and images from IPNs were taken with a transmission electron microscope (TEM).

Small-angle x-ray scattering was used to characterize the single-particle scattering factors produced by poly(amidoamine) dendrimers, poly(propleneimine) dendrimers, and polyol hyperbranched polymers in dilute solutions with methanol as solvent. Fits from electron density modeling reveal similar overall densities of the dendrimers as a function of dendrimer generation. The seventh through tenth generation poly(amidoamine) dendrimers exhibit higher order scattering features that require nearly monodisperse, spherical particles with essentially uniform internal segment densities. Dilute hyperbranched polymer solutions exhibit scattering more indicative of the inherent irregularity of internal segment densities and overall sizes to be expected within these systems. Radii of gyration estimated from electron density modeling agree reasonably well with those estimated by standard Guinier methods used in previous studies. (C) 1997 John Wiley & Sons, Inc.

ADVERTISEMENT RETURN TO ISSUEPREVCommunication to the...Communication to the EditorNEXTEvidence of a Novel Side Chain Structure in Regioregular Poly(3-alkylthiophenes)T. J. Prosa, M. J. Winokur, and R. D. McCulloughView Author Information Department of Physics, University of Wisconsin, Madison, Wisconsin 53706 Department of Chemistry, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213Cite this: Macromolecules 1996, 29, 10, 3654–3656Publication Date (Web):May 6, 1996Publication History Received11 October 1995Revised23 February 1996Published online6 May 1996Published inissue 1 January 1996https://pubs.acs.org/doi/10.1021/ma951510uhttps://doi.org/10.1021/ma951510urapid-communicationACS PublicationsCopyright © 1996 American Chemical SocietyRequest reuse permissionsArticle Views2806Altmetric-Citations324LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-Alertsclose SUBJECTS:Chemical structure,Crystal structure,Layered materials,Physical and chemical processes,Polymers Get e-Alerts

Comprehensive x-ray-diffraction data and structure factor calculations are presented for oriented poly(3-octylthiophene) films intercalated by iodine vapor to ${\mathrm{I}}_{3}^{\mathrm{\ensuremath{-}}}$ concentrations of 0, 4, 14, 26, and 45 mol wt. % per octylthiophene monomer. These data reconfirm previous reports that this polymer-iodine complex exhibits a continuous and reversible structural evolution. [M. J. Winokur, P. Wamsley, J. Moulton, P. Smith, and A. J. Heeger, Macromolecules 24, 3812 (1991); T. J. Prosa, M. J. Winokur, J. Moulton, P. Smith, and A. J. Heeger, Synth. Met. 55, 370 (1993); J. Moulton and P. Smith, ibid. 40, 13 (1991)]. Structure factor modeling calculations are used to fully specify the overall changes in the three-dimensional host polymer structure. This molecular restructuring involves both translational and rotational rearrangements of the host polymer. The fundamental lamellar base structure of the pristine host polymer is found to remain fully intact throughout the entire structural transformation. The large-scale changes in the observed interlayer repeat distances result from continuous variations in the angular orientation of the polymer backbone and in the average position of the alkyl side chains. Translational displacements of the polymer chains parallel to the main chain axes are found to occur within individual lamellae and this motion creates essentially one-dimensional intercalant channels perpendicular to the main chain axis. This latter process facilitates iodine intercalation and is, in part, responsible for the ability to achieve the very high iodine concentrations which have been measured experimentally. Scattering features are seen at the highest iodine concentrations which are indicative of additional structural ordering by the intercalant within the newly formed one-dimensional columns.