Two‐Photon Pattern Bleaching for Characterizing Structural Changes in Polymer Films

Using two‐photon absorption, an array of spots in a dye‐doped polymer film can be bleached, creating a three‐dimensional structure that can be imaged with two‐photon or confocal microscopy. Microscopic deformations resulting from various treatments to the film can be characterized, for example, swelling or shrinking. This technique is demonstrated on dye‐doped poly(vinyl alcohol), in which the effect of swelling with the addition of water to the film is shown.

     

Uniform Sub‐Micron Polymer Spheres Coated with Ag Nanoparticles

Summary: The synthesis of well‐defined uniform and spherical sub‐micron polymeric spheres, specifically poly[styrene‐co‐(glycidyl methacrylate)] (PSGMA) with a uniform size distribution and surface chemical functionality, is described. It is shown that the surface can be modified with a multi‐amine functional polymer, polyethyleneimine (PEI), most likely through covalent bonding in addition to electrostatic attraction. The PEI acts both as a stabilizing agent and a complexation agent for the deposition of noble metal Ag nanoparticles.

Reaction of PSGMA samples with excess PEI, and its TEM image.     

Stabilization of Polymer Bilayers by Introducing Crosslinking at the Interface

Summary: Bisphenol A solid epoxy serves as an effective reaction compatibilizer to the bisphenol A polycarbonate (PC)/PMMA bilayer systems. Addition of epoxy to the bottom PMMA layer can retard or even prevent the dewetting of PC films by introducing crosslinking between both components at the interface. This is the first investigation of polymer bilayers stabilized by chemical reactions.

AFM topographic image of a representative dewetting hole.     

Self‐supporting Polymer from a POSS Derivative

A new polyhedral oligomeric silsesquioxane macromer, octakis[N‐(6‐aminopyridin‐2‐yl)undecanamide‐10‐dimethyl‐siloxy]silsesquioxane (POSS‐C11‐Py), containing eight diaminopyridine arms, is able to self‐assemble to form a physically crosslinked polymer‐like structure with good mechanical properties (tensile strength = 46.1 MPa, tensile modulus = 0.58 GPa, elongation = 49.3%) through quadruple hydrogen bonding interactions between these arms. POSS‐C11‐Py is the first organic/inorganic supermolecule possessing polymer‐like mechanical properties as a result of self‐complementary interactions, providing a potential route toward the design and fabrication of polymer‐like supramolecular materials.

     

Cross‐Linked Conjugated Polymers for Achieving Patterned Three‐Color and Blue Polymer Light‐Emitting Diodes with Multi‐Layer Structures

Reactions between the ethylene groups in the backbone of conjugated polymers under UV illumination and heat treatment result in the cross‐linking of the main polymer chains. The cross‐linking leads to two simultaneous results in the polymer: excellent solvent resistance and increased bandgap. Using this reaction, three‐color polymer light‐emitting diodes (PLEDs) with a multi‐layer structure can be easily realized by a dry photo‐pattern in an active‐gas‐free environment. Multi‐layer blue devices with dramatically enhanced efficiency can also be achieved conveniently.

     

Synthesis of Polymer Brushes Using Atom Transfer Radical Polymerization

Atom transfer radical polymerization (ATRP) is a robust method for the preparation of well‐defined (co)polymers. This process has also enabled the preparation of a wide range of polymer brushes where (co)polymers are covalently attached to either curved or flat surfaces. In this review, the general methodology for the synthesis of polymer brushes from flat surfaces, polymers and colloids is summarized focusing on reports using ATRP. Additionally, the morphology of ultrathin films from polymer brushes is discussed using atomic force microscopy (AFM) and other techniques to confirm the formation of nanoscale structure and organization.

Formation of polymer brushes by ATRP.     

Multiscale Modeling of Branch Length in Butyl Acrylate Solution Polymerization

Branch lengths resulting from both backbiting and intermolecular chain transfer to polymer are examined for the solution polymerization of butyl acrylate, using a rate‐equation model and ordinary differential equations. Backbiting is allowed to generate branches of varying length, according to a cumulative distribution function obtained from a lattice kinetic Monte Carlo simulation. About 8% of the branches produced by backbiting are 10 mers or longer. In contrast to common assumptions about the origins of short‐chain and long‐chain branches, the model indicates that nearly all of the long‐chain branches may be produced by backbiting, rather than intermolecular chain transfer to polymer.

     

Polymer Crystallization Influenced by Initial Orientation of Cylindrical Diblock Copolymers in Thin Films

The effect of the initial states (disordered perpendicular cylinder structure vs. parallel cylinder structure) on the crystallization of polystyrene‐block‐poly(ethylene oxide) (PS‐b‐PEO) thin films during cyclohexane annealing was investigated. The cylindrical domains perpendicular or parallel to the surface were obtained by controlling the film thickness. During solvent annealing, for the film with the perpendicular cylinders, the ordering degree of cylinders was increased. The enthalpic increase is large enough for the forming of square‐shaped crystals, and subsequently the square‐shaped single crystals surrounded by the ordered hexagonally packed perpendicular cylinders evolved to the dendrite ones. For the film with the parallel cylinders, the parallel cylinders were translated to the perpendicular ones. The increased enthalpy was not large enough for the formation of square‐shaped single crystals. Instead, the dendrite‐like crystals started at the edge of terraces.

     

Preparation of Highly Transparent and Thermally Stable Films of α‐Cyclodextrin/Polymer Inclusion Complexes

Films of an α‐cyclodextrin/poly(ε‐caprolactone) inclusion complex have been successfully prepared and show high transparency and heat resistance in comparison to the pure polymer film. The physical properties, such as transparency, mechanical properties, and thermal stability, of the α‐CD‐PCL‐IC films are found to depend on the α‐cyclodextrin‐to‐polymer stoichiometry.

     

Probing Nanoscale Polymer Interactions by Forced‐Assembly

When two immiscible polymers are brought into intimate contact, highly localized mixing of polymer chains creates an “interphase” region. Materials that are entirely interphase are fabricated by forced‐assembly using layer‐multiplying coextrusion to form assemblies of thousands of nanolayers. Analysis of the interphase materials with conventional methods of polymer analysis confirms certain theoretical predictions for the first time. The unique properties of the new interphase materials result from lower free volume than the constituents.

Atomic force microscopy phase image from the cross‐section of a PC/PMMA nanolayer film with 4096 layers and average layer thickness of 25 nm.     

A Novel Route for Fabricating Metal‐Polymer Composite Nanoparticles with Phase‐Separated Structures

Au nanoparticles (NPs) and polymer composite particles with phase‐separation structures were prepared based on phase separation structures. Au NPs were successfully synthesized in amphiphilic block‐copolymer micelles, and then composite particles were formed by a simple solvent evaporation process from Au NPs and polymer solution. The phase separated structures (Janus and Core‐shell) were controlled by changing the combination of polymers having differing hydrophobicity.

     

Synthesis with Single Macromolecules: Covalent Connection between a Neutral Dendronized Polymer and Polyelectrolyte Chains as well as Graphene Edges

Single chains of a neutral, dendronized polymer with peripheral azide groups ( PG3A ) are co‐deposited onto molecularly modified graphite substrates with a positively charged dendronized polymer ( PG2 ) as well as with negatively charged plasmid dsDNA. PG3A is also prepared near graphite step‐edges. Single PG3A chains are moved with a scanning force microscope tip, into close contact with either of the two polyelectrolytes, as well as the step‐edge at predetermined positions. Treating these structures in situ with UV light leads to photochemically induced cross‐linking between the PG3A chains carrying azide groups and PG2 , dsDNA, and graphite step‐edges, respectively, which is proven by mechanically challenging the “welding” points by pulling on the molecules with the SFM‐tip.

     

A Conjugated Polymer‐Based Electrochemical DNA Sensor: Design and Application of a Multi‐Functional and Water‐Soluble Conjugated Polymer

In this work, we report the design of a new multi‐functional, water‐soluble conjugated polymer integrating both a DNA intercalator and a redox label. Based on this multi‐functional conjugated polymer, we develop a sequence‐specific electrochemical DNA sensor, where the acridine unit serves as the basis for sequence discrimination, and the ferrocene label provides the electrochemical signal. Moreover, the conjugated polythiophene helps transfer electrons from ferrocene to the electrode. This sensor provides a new way for rapid and convenient detection of DNA targets.

     

A Composite Polymer Film with both Superhydrophobicity and Superoleophilicity

Summary: A composite film composed of porous polyurethane (PU) and polystyrene (PS) microspheres with both superhydrophobicity and superoleophilicity has been prepared. In this film, the dual‐scale structure enhances both the hydrophobicity and oleophilicity of the surface material. The composite film with such an ‘intelligent’ wettability property can be utilized to separate oil and water systems efficiently.

The composite film can be used to separate diesel oil and water.     

New Poly(propylene glycol)‐ and Poly(ethylene glycol)‐Based Polymer Gelators with L‐Lysine

Summary: New polymer gelators consisting of poly(propylene glycol) or poly(ethylene glycol) and L ‐lysine‐based low‐molecular‐weight gelators have been developed. These polymer gelators were synthesized according to a simple procedure with high reaction yield, and formed organogels in many organic solvents. The organogelation mechanism was proposed from the transmission electron microscopy and FTIR spectroscopy studies.

Structures of the polymer gelators synthesized here.     

Energy Transfer from Locally Excited π* to Charge Transfer Ground States in a Silylene–π Hetero‐Junction Polymer

Summary: The silylene–π conjugating polymer, poly(di‐n‐hexylsilylenephenylene‐ethynylenephenylene) ( 1 ) adopted a fairly flexible coil‐like conformation due to the bent structure of silylene moiety and showed a unique photoexcited energy transfer behavior. The UV‐vis absorption and steady‐state/time‐resolved photoluminescence studies revealed the occurrence of an intramolecular photoexcited energy transfer (IET) between locally excited π* to charge transfer ground states as well as an intramolecular charge transfer (ICT).

The silylene–π conjugating polymer, poly(di‐n‐hexylsilylenephenylene‐ethynylenephenylene) showing a unique photoexcited energy transfer behavior.     

Thermosensitive and Dissolution Properties in Nanocomposite Polymer Hydrogels

We investigate the phase transition behavior and dissolution resistant properties of thermo‐sensitive nanocomposite hydrogels made from PEO‐PPO‐PEO triblock copolymer (Pluronic F127) and Laponite silicate nanoparticles. The rapid dissolution properties of F127 copolymer hydrogels usually limit their use as sustained release drug carriers. We overcome this limitation by synergistic combination of nanoparticle gelation characteristics with polymer thermo‐sensitivity. We present a proof of concept that the temperature‐dependent phase transitions can be shifted as a function of hydrogel composition and that the dissolution of the polymer hydrogels as well as the release of a model drug, albumin, can be significantly slowed down by addition of nanoparticles. The dissolution resistant properties generated will prove useful in the future formulation, processing and application of our polymer hydrogels for sustained release drug delivery carriers.

     

Post‐Functionalization of Polymers via Orthogonal Ligation Chemistry

The establishment of advanced living/controlled polymerization protocols allows for engineering synthetic polymers in a precise fashion. Combining advanced living/controlled polymerization techniques with highly efficient coupling chemistries facilitates quantitative, modular, and orthogonal functionalization of synthetic polymer strands at their chain termini as well as side‐chain functionalization. The review highlights the current status of selected post‐functionalization techniques of polymers via orthogonal ligation chemistries, major characteristics of the specific transformation chemistry, as well as the characterization of the products.

     

Patterning Proteins on Surfaces of Cross‐Sectioned Multilayer Polymer Films

Summary: A new approach is introduced to create submicrometer patterned surfaces using multilayer polymer films that contain alternating layers of two polymers, linear low‐density polyethylene (LLDPE) and ethylene‐co‐(acrylic acid) copolymer (EAA). Patterned templates have been prepared by microtoming the multilayer molded sheets. Regionally confined chemical functionality is confirmed by grafting an amine‐terminated biotin and adsorbing streptavidin specifically on the alternating layers of EAA.

Fluorescence micrograph of the Alexa488‐streptadivin patterned polymer surface.