We investigated the thermoresponsive behavior of aqueous solutions of star-shaped and linear poly(N,N-dimethylaminoethyl methacrylate) (PDMAEMA). The observed cloud points strongly decrease with increasing pH of the solution. This is explained by a weak charging of the star polymers with decreasing pH. A significant decrease of the cloud points with increasing molecular weight for high pH, i.e., for the almost uncharged state, was found to be virtually independent of the arm number and arm length. These findings are explained by classical Flory-Huggins theory. The increase of cloud points upon charging is captured by introduction of an effective degree of polymerization. Polymers with shorter arms show slightly higher cloud points at low pH than polymers with longer arms. The intramolecular segment density also influences the observed apparent pK b values, leading to higher values for stars with higher arm numbers.

Amphiphilic diblock copolymers, poly(n-butyl acrylate)-block-poly(acrylic acid) (PnBA-PAA), with narrow molecular weight distribution (PDI ≤ 1.07) were prepared by atom transfer radical polymerization (ATRP) of n-butyl acrylate and tert-butyl acrylate (tBA), followed by selective acidolysis of the PtBA block. These polymers possess a soft PnBA hydrophobic block with a constant chain length of 90−100 monomer units and pH- and ionic strength-sensitive hydrophilic PAA block with DPPAA = 33−300 AA monomer units. They were expected to form stimuli-responsive micelles. The block copolymers with DPPAA ≥ 100 are directly soluble in water at pH > 4.7. Pyrene steady-state fluorescence spectroscopy and fluorescence correlation spectroscopy (FCS) studies indicate the existence of a very low critical micelle concentration (cmc ∼ 10-8 mol/L). The number-average hydrodynamic radii of the micelles, as determined by FCS, range from 28 to 55 nm, depending on the PAA block length. FCS data indicate that micellar sizes significantly decrease upon dilution for salt-free systems. This is attributed to a dynamic, but kinetically controlled, behavior of these self-assembled nanostructures. In saline solutions the micellar sizes remain constant above the “apparent” cmc (cmc*), which is attributed to slower dynamics of unimer exchange between micelles.

We report the structure and dynamics of micelles of the amphiphilic diblock copolymers poly(nbutyl acrylate)-block-poly(acrylic acid) (PnBA-PAA). These self-assembled nanostructures consist of a liquid hydrophobic core and a pH-and ionic strength-sensitive hydrophilic corona. In the first part of this series, 1 we reported the synthesis and micellization of these block copolymers in aqueous media without the need of any cosolvent. Here we present a detailed study on the structural and dynamic properties of these micelles in aqueous solutions under various conditions using static and dynamic light scattering (SLS, DLS), small-angle neutron scattering (SANS), and cryogenic transmission electron microscopy (cryo-TEM). The block copolymers spontaneously dissolve in water, forming rather monodisperse micelles. Although the corona thickness depends on external stimuli, such as pH and salinity, the micelles do not significantly change their shape or aggregation number upon modifications of these parameters, in spite of the liquidlike nature of the hydrophobic block at room temperature. Moreover, the structure of the formed micelles depends on the preparation conditions: aggregates of micelles are initially formed when the polymers are dissolved in saline aqueous solutions even at pH 6.5, which disintegrate within weeks, resulting in isolated micelles with significantly larger size compared to micelles at the same ionic strength but initially prepared in the absence of added salt. The results are explained in terms of a kinetic control of the micellization process, which is dynamic in terms of unimer exchange but slow on the experimental time scale in adapting to external stimuli.

The formation of multicompartment micelles featuring a “spheres on sphere” core morphology in acetone as a selective solvent is presented. The polymers investigated are ABC triblock terpolymers, polybutadiene-b-poly(2-vinyl pyridine)-b-poly(tert-butyl methacrylate) (BVT), which were synthesized via living sequential anionic polymerization in THF. Two polymers with different block lengths of the methacrylate moiety were studied with respect to the formation of multicompartmental aggregates. The micelles were analyzed by static and dynamic light scattering as well as by transmission electron microscopy. Cross-linking of the polybutadiene compartment could be accomplished via two different methods, “cold vulcanization” and with photopolymerization after the addition of a multifunctional acrylate. In both cases, the multicompartmental character of the micellar core is fully preserved, and the micelles could be transformed into core-stabilized nanoparticles. The successful cross-linking of the polybutadiene core is indicated by 1H NMR and by the transfer of the aggregates into nonselective solvents such as THF or dioxane.

We report on interpolyelectrolyte complexes (IPECs) formed by micelles of ionic amphiphilic diblock copolymers with polyisobutylene (PIB) and poly(sodium methacrylate) (PMANa) blocks interacting with quaternized poly(4-vinylpyridine) (P4VPQ). The interpolyelectrolyte complexation was followed by turbidimetry and small angle neutron scattering (SANS). The data obtained by means of a combination of SANS, dynamic light scattering (DLS), and cryogenic transmission electron microscopy (cryo-TEM) provide evidence on the core-shell-corona structure of the complex species with the shell assembled from fragments of electrostatically bound PMANa and quaternized P4VPQ fragments, original PIBx-b-PMAAy micelles apparently playing a lyophilizing part. The complex formation is followed by potentiometric titration as well. This process is initially kinetically controlled. In the second step larger aggregates rearrange in favor of smaller complexes with core-shell-corona structure, which are thermodynamically more stable. An increase in ionic strength of the solution results in dissociation of the complex species as proven by SANS and analytical ultracentrifugation (AUC). This process begins at the certain threshold ionic strength and proceeds via a salt-induced gradual release of chains of the cationic polyectrolyte from the complex species.

Block copolymers consisting of incompatible components self-assemble into microphase-separated domains yielding highly regular structures with characteristic length scales of the order of several tens of nanometres. Therefore, in the past decades, block copolymers have gained considerable potential for nanotechnological applications, such as in nanostructured networks and membranes, nanoparticle templates and high-density data storage media. However, the characteristic size of the resulting structures is usually determined by molecular parameters of the constituent polymer molecules and cannot easily be adjusted on demand. Here, we show that electric d.c. fields can be used to tune the characteristic spacing of a block-copolymer nanostructure with high accuracy by as much as 6% in a fully reversible way on a timescale in the range of several milliseconds. We discuss the influence of various physical parameters on the tuning process and study the time response of the nanostructure to the applied field. A tentative explanation of the observed effect is given on the basis of anisotropic polarizabilities and permanent dipole moments of the monomeric constituents. This electric-field-induced effect further enhances the high technological potential of block-copolymer-based soft-lithography applications.

We utilize inelastic incoherent neutron scattering (INS) to quantify how fullerenes affect the ‘fast’ molecular dynamics of a family of polystyrene related macromolecules. In particular, we prepared bulk nanocomposites of (hydrogenous and ring-deuterated) polystyrene and poly(4-methyl styrene) using a rapid precipitation method where the C60 relative mass fraction ranged from 0% to 4%. Elastic window scan measurements, using a high resolution (0.9 µeV) backscattering spectrometer, are reported over a wide temperature range (2–450 K). Apparent Debye–Waller (DW) factors , characterizing the mean-square amplitude of proton displacements, are determined as a function of temperature, T. We find that the addition of C60 to these polymers leads to a progressive increase in relative to the pure polymer value over the entire temperature range investigated, where the effect is larger for larger nanoparticle concentration. This general trend seems to indicate that the C60 nanoparticles plasticize the fast (≈10−15 s) local (≈1 Å) dynamics of these polymer glasses. Generally, we expect nanoparticle additives to affect polymer dynamics in a similar fashion to thin films in the sense that the high interfacial area may cause both a speeding up and slowing down of the glass state dynamics depending on the polymer–surface interaction.

Since the fi rst report on electric fi eld-induced alignment of block copolymers (BCPs) in 1991, electric fi elds have been shown not only to direct the orientation of BCP nanostructures in bulk, solution, and thin fi lms, but also to reversibly induce order-order transitions, affect the order-disorder transition temperature, and control morphologies' dimensions with nanometer precision. Theoretical and experimental results of the past years in this very interesting fi eld of research are summarized and future perspectives are outlined. C. Liedel , C. W. Pester , A. Böker Lehrstuhl für Makromolekulare Materialien und Oberfl ächen, DWI an der RWTH Aachen e.Clemens Liedel studied chemistry and macromolecular science (in the framework of the Elite Network of Bavaria) at Bayreuth University and recieved his diplomas in 2008 and 2010, respectively. Since 2008, he has been working on his Ph.D. degree in Bayreuth and Aachen in the group of Prof. A. Böker with an included research period at the University of California Santa Barbara (UCSB) in the group of Prof. E. J. Kramer. The topic of his current work is block copolymers and composite materials in thin fi lms exposed to electric fi elds. Christian W. Pester received his diploma in polymer and colloidal chemistry from Bayreuth University in 2009. The topic of his diploma thesis was electric-fi eld induced alterations of domain spacings. He then entered RWTH Aachen University and is pursuing his Ph.D. degree under the supervision of Prof. A. Böker. His current research interest focuses on the study of block copolymers in electric fi elds by small-angle scattering methods. Alexander Böker is a Full Professor at RWTH Aachen University for Macromolecular Materials and Surfaces and Co-Director of the DWI an der RWTH Aachen e.V. He studied chemistry at Cornell University and the University of Mainz, Germany, where he received his diploma in chemistry in 1999. In 2002, he completed his Ph.D. in physical and macromolecular chemistry at the University of Bayreuth. From 2002 to 2004, he worked with Thomas P. Russell at the University of Massachusetts, Amherst. His main research interests include guided self-assembly of block copolymer and nanoparticle systems, and their control via external fi elds.