Low‐Temperature Growth of Thick Polystyrene Brushes via ATRP

Summary: This contribution describes the graft polymerization of polystyrene (PS) by atom transfer radical polymerization at 50, 60, and 75 °C. Thick PS brushes were grown from initiator‐functionalized PGMA layers on silicon, and constant growth rates provide indirect evidence that the polymerizations were controlled.

Formation of polystyrene brushes at T < T_g by ATRP of styrene from α‐bromoester initiator‐functionalized poly(glycidyl methacrylate) layers.     

Co‐Continuous Polymeric Nanostructures via Simple Melt Mixing of PS/PMMA

Blends of polystyrene/poly(methyl methacrylate) (PS/PMMA) (30/70) prepared by simple melt mixing form a droplet (PS) in‐matrix (PMMA) morphology. It is found that addition of a carefully designed copolymer PS‐b‐P(S‐ran‐MMA) (SSM) compatibilizer could convert the morphology into a co‐continuous system. Indeed, the continuity of the dispersed PS phase increased with an increase in PS‐b‐P(S‐ran‐MMA) content, and a fully co‐continuous morphology (continuity = 100%) was obtained at 20% SSM fraction with a characteristic size of 100 nm.

     

Supramolecular Assembly of Gold Nanoparticles Mediated by Polypseudorotaxane with Thiolated β‐Cyclodextrin

Summary: A water‐soluble gold nanoparticle aggregate 2 was prepared by chloroauric acid and a polypseudorotaxane 1 of mono‐6‐thio‐β‐cyclodextrin with poly(propylene glycol) bis(2‐aminopropyl ether) ( ≈ 2 000) in the presence of sodium borohydride in N,N‐dimethylformamide (DMF) solution. The investigative results indicated that the gold nanoparticle aggregate 2 might act as an efficient DNA‐cleavage reagent.

A typical TEM image of gold nanoparticle aggregate 2 .     

Ring and Disk‐Like CdSe Nanoparticles Stabilized with Copolymers

CdSe nanoparticles stabilized with the amphiphilic diblock copolymer polystyrene‐block‐poly(4‐vinylpyridine) were spread from toluene dispersion on the water surface. Monolayers could be transferred onto solid substrates using the Langmuir‐Blodgett technique. By means of atomic force and scanning electron microscopy highly symmetric ring and disk‐like structures with diameters ranging between 150 nm and 1200 nm were observed.

AFM image of a mixed monolayer of copolymer 12 and CdSe nanoparticles stabilized with polystyrene‐block‐poly(4‐vinylpyridine).     

Nanostructured Heteroarm Star Block Terpolymers via an Extension of the “In–Out” Polymerization Route

In this communication an extended “in–out” polymerization method is presented, which leads to the synthesis of novel heteroarm star block terpolymers of the type A_n(B‐b‐C)_n. A four step/one‐pot synthetic procedure is pursued using anionic polymerization under an inert atmosphere. The resulted star‐shaped terpolymer consists of a divinyl benzene nodule bearing pure polystyrene and poly(hexyl methacrylate)‐block‐poly(methyl methacrylate) diblock copolymer arms. It is shown that this kind of star terpolymers can self‐assemble in the bulk forming lamellae mesophase by arm and block segregation. The mechanical properties of the terpolymer have been examined in detail. Finally, the proposed synthetic procedure can be easily employed in other controlled polymerization methods.

     

Synthesis of Well‐Defined Polybenzamide‐block‐Polystyrene by Combination of Chain‐Growth Condensation Polymerization and RAFT Polymerization

Well‐defined diblock copolymers composed of poly(N‐octylbenzamide) and polystyrene were synthesized by reversible addition‐fragmentation chain transfer (RAFT) polymerization of styrene with a polyamide chain transfer agent (CTA) prepared via chain‐growth condensation polymerization. Synthesis of a dithioester‐type macro‐CTA possessing the polyamide segment as an activating group was unsatisfactory due to side reactions and incomplete introduction of the benzyl dithiocarbonyl unit. On the other hand, a dithiobenzoate‐CTA containing poly(N‐octylbenzamide) as a radical leaving group was easily synthesized, and the RAFT polymerization of styrene with this CTA afforded poly(N‐octylbenzamide)‐block‐polystyrene with controlled molecular weight and narrow polydispersity.

     

Self‐Assembling Nanomaterials using Magnetic Nanoparticles Modified with Polystyrene Brushes

Magnetic nanomaterials have been studied in order to generate novel nanocomposites that display both the magnetic properties of the nanoparticles and the ability to self‐assemble of the amorphous block copolymer matrix. Towards this goal, iron oxide magnetic nanoparticles have been modified with PS brushes by ATRP in order to improve both the dispersion and the affinity of the nanoparticles with one of the blocks of a polystyrene‐block‐polybutadiene‐block‐polystyrene block copolymer. This method of preparation of nanocomposites opens new strategies for the generation of magnetic nanomaterials. The samples are characterized using DSC and atomic and magnetic force microscopies.

     

Penultimate Propagation Kinetics of Butyl Methacrylate,Butyl Acrylate,and Styrene Terpolymerization

The pulsed‐laser polymerization technique is used to determine the composition‐averaged free‐radical propagation rate coefficient (k_p,ter) for terpolymerization of butyl methacrylate, butyl acrylate, and styrene between 60 and 120 °C. A significant deviation from terminal model predictions is observed for the ternary system, indicating that penultimate kinetics are important at these industrially relevant temperatures. The implicit penultimate propagation model, with all the coefficients taken from previous studies of the binary systems, provides a good prediction of the experimental k_p,ter results.

     

A Strategy for Synthesis of Ion‐Bonded Supramolecular Star Polymers by Reversible Addition‐Fragmentation Chain Transfer (RAFT) Polymerization

We have developed a novel strategy for the preparation of ion‐bonded supramolecular star polymers by RAFT polymerization. An ion‐bonded star supramolecule with six functional groups was prepared from a triphenylene derivative containing tertiary amino groups and trithiocarbonate carboxylic acid, and used as the RAFT agent in polymerizations of tert‐butyl acrylate (tBA) and styrene (St). Molecular weights and structures of the polymers were characterized by ¹H NMR and GPC. The results show that the polymerization possesses the character of living free‐radical polymerization and the ion‐bonded supramolecular star polymers PSt, PtBA, and PSt‐b‐PtBA, with six well‐defined arms, were successfully synthesized.

     

Synthesis and Characterization of Helix‐Coil Diblock Copolymers with Controlled Supramolecular Architectures in Aqueous Solution

Summary: A series of helix‐coil diblock copolymers based on poly(ethylene oxide) and optically active helical poly{(+)‐2,5‐bis[4′‐((S)‐2‐methylbutoxy)phenyl]styrene} (PMBPS) were synthesized via atom transfer radical polymerization (ATRP). The synthetic methodology permitted straightforward preparation of the diblock copolymers with relatively low polydispersities and a broad range of compositions and molecular weights. Depending on the composing block length and the initial concentration, the copolymers self‐assembled into different supramolecular structures in aqueous solution, including spherical micelles, vesicles, multilamellar vesicles, large compound vesicles, and tubules.

Schematic representation of the synthesis of PEO‐b‐PMBPS block copolymers and their aggregation in aqueous solution.     

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.

     

Defined Poly[styrene‐block‐(ferrocenylmethyl methacrylate)] Diblock Copolymers via Living Anionic Polymerization

Ferrocenylmethyl methacrylate (FMMA) is one of the very few metallocene‐based monomers that are promising candidates for truly living anionic polymerization. Nevertheless, FMMA homopolymers with a narrow polydispersity, or block copolymerization studies that result in satisfying blocking efficiencies, are unknown so far. Here we describe a procedure that leads to highly regular FMMA‐based polymers for the first time, characterized by polydispersity indices (PDI) of less that 1.05 and very high blocking efficiencies (>95%) in sequential copolymerization with styrene. Some of the obtained poly[styrene‐block‐(ferrocenylmethyl methacrylate)]s show unusual microphase morphologies, presumably the consequence of high T_gs causing ‘frustrated’ non‐equilibrium states.

     

Chemoenzymatic Synthesis of Polycaprolactone‐block‐Polystyrene via Macromolecular Chain Transfer Reagents

ε‐Caprolactone (CL) was enzymatically polymerized with 2‐mercaptoethanol as the initiator, both in an oil bath and under microwave (MW) irradiation. The polymerization performed under MW irradiation maintaining equal conditions led to higher yields and less formation of side products, i.e., a higher chemoselectivity was observed. The resulting polyester with a terminal  SH moiety had a of 3 600 g · mol⁻¹, determined by size exclusion chromatography (SEC), and was used as a chain transfer reagent. Subsequent copolymerization with styrene in different ratios led to polycaprolactone‐block‐polystyrene. SEC analysis and polarization microscopy of crystallized samples with different styrene contents proved the formation of block copolymers.

     

“Click” Dielectrics: Use of 1,3‐Dipolar Cycloadditions to Generate Diverse Core‐Shell Nanoparticle Structures with Applications to Flexible Electronics

We have synthesized a “universal ligand” incorporating a phosphonate surface anchor and a terminal alkyne moiety which binds to TiO₂ nanoparticles and exhibits excellent dispersity in organic solvents. The alkyne functionality permits attachment of azide terminated polymer shells using “click” chemistry. Thus TiO₂ core nanoparticles have been encapsulated with both polystyrene and poly(t‐butyl acrylate) shells. The TiO₂‐poly(t‐butyl acrylate) core shell nanoparticles are amenable to further chemical transformation into TiO₂‐poly(acrylic acid) nanoparticles through ester hydrolysis. These TiO₂‐polyacrylic acid nanoparticles are dispersible in aqueous solution. The resulting core‐shell nanoparticles have been incorporated as high K dielectric films in capacitor and organic thin film transistor devices and are promising new materials for flexible electronics applications.

     

Combining Steric and Electrostatic Stabilization Using Hydrophilic MacroRAFT Agents in an Ab Initio Emulsion Polymerization of Styrene

Hydrophilic (co)polymers carrying a thiocarbonyl thio end group such as poly(dimethylaminoethyl methacrylate), poly(ethylene oxide), and poly(ethylene oxide)‐block‐poly(dimethylaminoethyl methacrylate) have been evaluated as precursors of stabilizers in batch ab initio emulsion polymerization of styrene under acidic conditions to form electrosterically stabilized polystyrene latex particles. As a mixture of P(DMAEMA/H⁺Cl⁻)‐RAFT and PEO‐RAFT failed to give satisfactory results, PEO‐RAFT was used as a control agent for the RAFT polymerization of DMAEMA, and the resulting block copolymer was successfully used in ab initio styrene emulsion polymerization.

     

High Solids Content,Soap‐Free,Film‐Forming Latexes Stabilized by Laponite Clay Platelets

High solids content film‐forming poly[styrene‐co‐(n‐butyl acrylate)] [poly(Sty‐co‐BuA)] latexes armored with Laponite clay platelets have been synthesized by soap‐free emulsion copolymerization of styrene and n‐butyl acrylate. The polymerizations were performed in batch in the presence of Laponite and a methyl ether acrylate‐terminated poly(ethylene glycol) macromonomer in order to promote polymer/clay association. The overall polymerization kinetics showed a pronounced effect of clay on nucleation and stabilization of the latex particles. Cryo‐transmission electron microscopy observation confirmed the armored morphology and indicated that the majority of Laponite platelets were located at the particle surface. The resulting nanostructured films displayed enhanced mechanical properties.

     

Square Lamellar Structure Having Phase‐Separated Microdomain in H‐Shaped Block Copolymer Thin Film

The morphology of a H‐shaped block copolymer (poly(ethylene glycol) backbone and polystyrene branches (PS)₂PEG(PS)₂) in a thin film has been investigated. A peculiar square lamella that has a phase‐separated microdomain at its surface is obtained after spin coating. The experimental temperature plays a critical role in the lamellar formation. The copolymer first self‐assembles into square lamellar micelles with an incomplete crystalline core due to the crystallizability of PEG. In the subsequent process of solvent evaporation, phase separation between PS and non‐crystalline PEG attached at the chain‐folded PEG surface takes place, which results in phase‐separated microdomains being formed at the lamellar surface.

     

Terminal Modification with 1‐Adamantylamine to Endow Hyperbranched Polyamidoamine with Thermo‐/pH‐Responsive Properties

A novel terminal modification agent to endow hyperbranched polyamidoamine (HPAMAM) with thermo‐/pH‐responsive properties is reported. HPAMAM with terminal vinyl groups is first synthesized and then end‐capped by 1‐adamantylamine (ADA). The resulting hyperbranched polymer (HPAMAM‐ADA) shows interesting thermo‐responsive properties in aqueous solution, which have been investigated by UV‐vis spectroscopy, optical microscopy, and ¹H NMR spectroscopy. The lower critical solution temperature can be controlled by adjusting the end‐capping ratio of ADA. In addition, HPAMAM‐ADA exhibits a pH‐dependent water solubility. This pH‐responsive behavior is also studied.

     

Pulling Polymers on Energetically Disordered Surfaces: Molecular Dynamics Tests of Linear and Non‐linear Response

Equilibrium and non‐equilibrium molecular dynamics simulations of flexible polymer chains absorbed on heterogeneous surfaces are presented. The surfaces are flat but energetically disordered, consisting of a random mixture of weakly and more strongly absorbing sites (94 and 6%, respectively). For comparison, the two corresponding homogeneous surfaces are also simulated. This apparently weak energetic disorder can produce significant changes of the chain statistics, equilibrium dynamics, and non‐equilibrium response to a horizontal pulling force. On the disordered surfaces, the polymer–surface effective friction coefficient becomes strongly force‐dependent, as the dominant mode of motion changes from localized stick–slip events to smooth and continuous sliding. This is strongly reminiscent of the Schallamach model of rubber friction and the Maier–Göritz picture of the Payne effect in filled elastomers.