Design and Synthesis of Fast‐Degrading Poly(anhydride‐esters)

Fast‐degrading, salicylate‐based poly(anhydride‐esters) were designed to degrade and release the active component, salicylic acid (SA), within 1 week. The polymer degradation was enhanced by using shorter or oxygen‐containing aliphatic chains. A copolymer of diglycolic acid was also made with a salicylate‐based diacid for comparison of polymer properties, including SA release. Both methods resulted in polyanhydrides with molecular weights ranging from 14 500 to 27 800 Da and displayed glass transition temperatures near physiological conditions, namely 33–40 °C. The homo‐ and copolymers completely degraded within one week releasing the chemically incorporated SA.

     

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.

     

All‐in‐one Layer: Anisotropic Emission due to Light‐Induced Orientation of a Multifunctional Polymer

An efficient procedure to create oriented polymer films with strongly anisotropic properties is described. It is based on a two‐step process combining a photochemical and a thermal aligning step. The orientation of the polymer parallel or perpendicular to linearly polarised incident light can be adjusted. The method presented allows for simple fabrication of films with anisotropic absorption and emission characteristics with a dichroism of 0.7 and a fluorescence anisotropy of about 8.

     

Preparation of Magnetite Nanoparticles Coated with an Amphiphilic Block Copolymer: A Potential Drug Carrier with a Core‐Shell‐Corona Structure for Hydrophobic Drug Delivery

Summary: The synthesis of magnetic magnetite nanoparticles coated with amphiphilic block copolymers of poly(ethyl methacrylate)‐block‐poly(2‐hydroxyethyl methacrylate) for use as new potential carriers for hydrophobic drug delivery is reported. The results show that a new core‐shell‐corona structural material is obtained with a very narrow molecular weight distribution of the hydrophobic segment (PDI = 1.10). UV‐Vis results show that 37% of progesterone is released from the nanoparticles after 22 h, much slower than free release (99% after 14 h), which demonstrates that the presence of the hydrophobic segment can effectively control the release of hydrophobic drugs.

Synthesis of an amphiphilic block polymer poly(ethyl methacrylate)‐block‐poly(2‐hydroxyethyl methacrylate) on magnetite nanoparticles and their use as potential drug carriers     

pH‐Responsive PEG‐Poly(β‐amino ester) Block Copolymer Micelles with a Sharp Transition

Summary: A pH‐sensitive block copolymer is synthesized by step polymerization and its pH‐sensitive micellization‐demicellization behavior is studied. This polymer has a hydrophilic MPEG (shell) and hydrophobic but pH‐sensitive poly(β‐amino ester) (core), which can form a self‐assembled micelle. As confirmed by fluorescence spectroscopy and dynamic light scattering (DLS), this polymer shows a sharp pH‐sensitive micellization‐demicellization behavior. It is confirmed that the pH sensitivity is affected by the molecular weight ratio between the MPEG and poly(β‐amino ester).

Plots of the intensity ratio I₃₃₇/I₃₃₄ (from pyrene excitation spectra): a) vs. pH for copolymer samples and b) vs. log (concentration) for M1.     

Synthesis of a New Thiophene/Quinoxaline CT‐Type Copolymer with High Solubility and Its Basic Optical Properties

A new π‐conjugated charge‐transfer‐type copolymer of electron‐donating thiophene and electron‐accepting quinoxaline was prepared by organometallic polycondensation. The polymer was soluble in organic solvents such as tetrahydrofuran, and showed a UV‐vis peak at long wavelengths of 598 nm in chloroform and 629 nm in the film. Its film exhibited a χ⁽³⁾ peak in the resonance region with a χ⁽³⁾ value comparable to that of regioregular head‐to‐tail poly(3‐hexylthiophene‐2,5‐diyl).

     

Influence of Cross‐Linking Density on the Glass Transition and Structure of Chemically Cross‐Linked PVA: A Molecular Dynamics Study

Mechanical properties and glass transitions of cross‐linked polymer networks depend strongly on both the network topology and cross‐linking density. A model is developed using a dynamic cross‐linking approach based on a cutoff distance criterion followed by a high‐temperature annealing procedure. The analysis focused on on the influence of cross‐linking degree on chain packing and hydrogen‐bond structure and on the roles played by various energy components in the glass transition process. T_g was calculated using two different methods; (i) from the intersection of lines drawn through points in a plot of specific volume versus temperature and (ii) from plots of different molecular energy components as a function of temperature.

     

Symmetric Versus Asymmetric “Homologous” Vinylic Cross‐Linkers in Two‐Components Networks: Formation of Pseudo‐Conetworks or Pseudo‐IPNs

Radical copolymerizations of heterologous comonomers are compositionally heterogeneous, unless the reaction is performed in continuous conditions. A bicomponent network prepared from a heterogeneous reaction like the mentioned before is therefore a complex structure where chains with different compositions are linked through the cross‐linker molecules. It is theoretically shown here that the use of cross‐linkers with different structural homologies toward the two comonomers may lead to very different topologies. Thus, a mixture of symmetric cross‐linkers, each one homologous to each comonomer, tends to form interpenetrated networks (IPNs). However, the use of a single bihomologous asymmetric cross‐linker, where each of the functionalities is homologous toward each of the comonomers, tends to form conetworks. It is shown here that the higher the differential reactivity between the groups, the higher is the tendency toward these extreme structures.

     

Cationic Salt‐Responsive Bottle‐Brush Polymers

A class of cationic bottle‐brush polymers that show ionic strength‐dependent stimuli responsiveness is prepared. Brush polymers with norbornene as backbone and quaternary ammonium (QA)‐containing polycaprolactone copolymers as side chains are synthesized by a combination of ring‐opening metathesis polymerization, ring‐opening polymerization, and click reaction. In water with low ionic strength, brush polymers are soluble due to the strong electrostatic repulsion between cationic QA groups. As the addition of salt to increase ionic strength, single brush polymers undergo a transition from extended conformation to collapsed state and finally become insoluble in solution due to the screening effect of salts that yield the once‐dominant electrostatic interactions among QA species to hydrophobic–hydrophobic interactions.

     

Small‐Angle Scattering From Branched Polymers

The single‐polymer form factor is determined for branched polymers using a scaling argument in order to recover the low‐Q Porod exponent characteristic of the overall structure. The high‐Q Porod exponent characterizes the local branching structure. An alternative approach based on a high‐Q expansion contains information about functionality, branch length and branch content. The specific case of a starburst dendrimer for which the form factor is known is discussed. The model predictions are compared to small‐angle neutron scattering data from a dilute solution of dendrimer in D₂O.

     

Direct Observation of Alkyl Chain Interdigitation in Conjugated Polyquarterthiophene Self‐Organized on Graphite Surfaces

A solution processible polymer—poly(3,3‴‐didodecylquaterthiophene) (PQT‐12) is investigated at the liquid/solid interface using the scanning tunneling microscopy (STM). Two‐dimensional ordered films made up of self‐assembled domains, with dimensions of 100 nm × 50 nm adsorbed on highly oriented pyrolytic graphite (HOPG) were formed. These domains consist of parallel lamellar polymer chains, with the alkyl chains forming interdigitated structures, along with U‐shaped and closed ring segments of the polymer chains. A polymer chain packing model is proposed herein, which attempts to propose a correlation between the packing of long chains and charge mobilities. These STM results could help in understanding the relationship between the extended conjugation and molecular organization of the PQT‐12 chains.

     

Synthesis and Characterization of Novel Mesogen‐Jacketed Liquid Crystalline Miktoarm Star Rod‐Coil Block Copolymer

Summary: A series of novel mesogen‐jacketed liquid crystal miktoarm star rod‐coil block copolymers were synthesized via atom transfer radical polymerization (ATRP). Their architectures {coil conformation of styrene segment and rigid rod conformation of {2,5‐bis[(4‐methoxyphenyl)oxycarbonyl]styrene} (MPCS) segment} were confirmed by GPC, ¹H NMR, and MALDI‐TOF studies. The liquid crystalline behaviors of the synthesized copolymers are evidenced from POM observation. The liquid crystalline phase depends on the molecular weights of the rigid rod arm of miktoarm star copolymers.

Miktoarm star rod‐coil block copolymer.     

Solvent Vapor‐Induced Nanowire Formation in Poly(3‐hexylthiophene) Thin Films

Summary: Nanowire lengths and length‐to‐width aspect ratios in regioregular poly(3‐hexylthiophene) (P3HT) were simply controlled through changes in the solvent vapor pressure during solidification. It is demonstrated that the nanowires grew by rod‐to‐rod association, in which the molecular long axis of the P3HT chains appeared to be well‐oriented parallel to the silicon substrate (Si/SiO_x). The formation of the nanowires took place by one dimensional self‐assembly, governed by π‐π stacking of the P3HT units.

TEM high contrast images showing P3HT nanowires fabricated by spin‐coating under a solvent vapor pressure.     

Polymer‐Based Rectifying Diodes on a Glass Substrate Fabricated by Ink‐Jet Printing

Summary: The fabrication of polymer diodes on a glass substrate by an ink‐jet printing technique is reported. Both an n‐type semiconductive polymer, poly[2‐methoxy‐5‐(2‐ethylhexyloxy)‐1,4‐(1‐cyanovinylene)phenylene] (CN‐PPV), and a p‐type semiconductive polymer, polypyrrole (PPy) or poly(3,4‐ethylenedioxythiophene) (PEDOT), were printed through a piezoelectric ink‐jet printer. The printed CN‐PPV/PPy and CN‐PPV/PEDOT diodes showed good rectifying characteristics. These results indicate the potential of the low‐cost ink‐jet printing technique to produce polymer microelectronic devices and circuits.

Schematic diagram of the printed polymer diode     

Redox‐ and Glucose‐Induced Shape‐Memory Polymers

A novel redox‐induced shape‐memory polymer (SMP) is prepared by crosslinking β‐cyclodextrin modified chitosan (β‐CD‐CS) and ferrocene modified branched ethylene imine polymer (Fc‐PEI). The resulting β‐CD‐CS/Fc‐PEI contains two crosslinks: reversible redox‐sensitive β‐CD‐Fc inclusion complexes serving as reversible phases, and covalent crosslinks serving as fixing phases. It is shown that this material can be processed into temporary shapes as needed in the reduced state and recovers its initial shape after oxidation. The recovery ratio and the fixity ratio are both above 70%. Furthermore, after entrapping glucose oxidase (GOD) in the system, the material shows a shape memory effect in response to glucose. The recovery ratio and the fixity ratio are also above 70%.

     

Self‐Assembly and Dispersion of Chromogenic Molecules: A Versatile and General Approach for Self‐Assessing Polymers

Summary: Self‐assessing polymer blends based on poly(ethylene terephthalate glycol) or linear low‐density polyethylene and small amounts (0.5–2% w/w) of chromogenic sensor dyes are prepared and investigated. The cyano‐substituted oligo(p‐phenylene vinylene) dyes employed in the study exhibit pronounced optical absorption changes upon self‐assembly, because of charge‐transfer interactions or conformation changes. The extent of dye aggregation (and therewith the optical absorption characteristics) in these blends is significantly influenced by exposure to external stimuli. Subjecting appropriately processed samples to either temperatures above their glass transition or mechanical deformation can significantly change the extent of aggregation, which in turn leads to a color change.

Mechano‐optical response of a 1.0% w/w LLDPE/C18‐RG blend film. Pristine films are orange due to aggregated dye molecules. Deformation leads to dispersion of the dye and irreversibly changes the color to yellow.     

Electro‐active Polymer Actuator Based on Sulfonated Polyimide with Highly Conductive Silver Electrodes Via Self‐metallization

We report here a facile synthesis of high performance electro‐active polymer actuator based on a sulfonated polyimide with well‐defined silver electrodes via self‐metallization. The proposed method greatly reduces fabrication time and cost, and obviates a cation exchange process required in the fabrication of ionic polymer‐metal composite actuators. Also, the self‐metallized silver electrodes exhibit outstanding metal‐polymer adhesion with high conductivity, resulting in substantially larger tip displacements compared with Nafion‐based actuators.

     

Micelles‐Encapsulated Microcapsules for Sequential Loading of Hydrophobic and Water‐Soluble Drugs

Layer‐by‐layer (LbL) assembly was conducted on CaCO₃ microparticles pre‐doped with polystyrene‐block‐poly(acrylic acid) (PS‐b‐PAA) micelles, and resulted in micelles encapsulation in the microcapsules after core removal. Distribution of the micelles in the templates and capsules was characterized by transmission electron microscopy and confocal laser scanning microscopy. The micelles inside the capsules connected with each other to form a chain and network‐like structure with a higher density near the capsule walls. The hydrophobic PS cores were then able to load small uncharged hydrophobic drugs while the negatively charged PAA corona could induce spontaneous deposition of water‐soluble positively charged drugs such as doxorubicin.

     

End‐to‐End Distances in Four‐Junction Polymers

The various end‐to‐end distances of four‐junction polymers are investigated. The sizes of the different kinds of equal length branches and the backbone of two different polymers, with either nine or eleven branches, are estimated by means of both renormalization‐group and MC calculations. The comparisons of first‐order ε = 4 − d predictions with the MC results are satisfactory. The same trends are present in both techniques. The excluded‐volume interactions from additional branches further expand the various parts of the chains so that internal branches are larger than external ones. The branch ratios in the eleven‐branch case are expanded even more than the corresponding ratios of the nine‐branch polymer.

     

Fabrication of a Metal Particle Array Based on a Self‐Assembled Template from a Two‐Armed Polymer

A two‐armed polymer with a crown ether core self‐assembles to produce macroporous films with pores perpendicularly reaching through the film down to the substrate. A possible assembling mechanism is discussed. The pore size can be conveniently adjusted by changing the solution concentration. These through‐hole macroporous films provide a template for fabricating an array of Cu nanoparticle aggregates.