Stimuli‐Responsive A‐b‐(B‐co‐C) Diblock Terpolymers Bearing Polyampholyte Sequences

Summary: Diblock terpolymers that consist of homopolymer and statistical copolymer (polyampholyte) building blocks are synthesized by group transfer polymerization. Two types of block tepolymers are explored in aqueous media: the amphiphilic poly{[(diethylamino)ethyl methacrylate]‐co‐(methacrylic acid)}‐block‐poly(methyl methacrylate) and the double hydrophilic poly[oligo(ethylene glycol) methacrylate]‐block‐poly{[(diethylamino)ethyl methacrylate]‐co‐(methacrylic acid)}. The first terpolymer self‐assembles in aqueous media to form responsive micelles that change their corona charge sign upon switching pH. The second terpolymer exhibits a multi‐responsive behavior. It forms neutral, positive, or negative micelles depending on a combination of different environmental conditions such as temperature, pH, and ionic strength.

P(DEAEMA‐co‐MAA)‐b‐PMMA pH‐sensitive micelles.     

Plasma‐Initiated Controlled/Living Radical Polymerization of Methyl Methacrylate in the Presence of 2‐Cyanoprop‐2‐yl 1‐dithionaphthalate (CPDN)

Summary: Plasma‐initiated controlled/living radical polymerization of methyl methacrylate (MMA) was carried out in the presence of 2‐cyanoprop‐2‐yl 1‐dithionaphthalate. Well‐defined poly(methyl methacrylate) (PMMA), with a narrow polydispersity, could be synthesized. The polymerization is proposed to occur via a RAFT mechanism. Chain‐extension reactions were also successfully carried out to obtain higher molecular weight PMMA and PMMA‐block‐PSt copolymer.

Dependence of ln([M]₀/[M]) on post‐polymerization time (above), and \overline M _{\rm n} and PDI against conversion (below) for plasma initiated RAFT polymerization of MMA at 25 °C.     

Patterning Layered Polymeric Multilayer Films by Room‐Temperature Nanoimprint Lithography

Summary: Polyelectrolyte multilayer films of poly(acrylic acid) (PAA)/poly(allylamine hydrochloride) (PAH) and PAH/poly(sodium 4‐styrenesulfonate) (PSS) based on electrostatic interactions as a driving force are patterned by room‐temperature nanoimprint lithography (RT‐NIL). Under an imprinting pressure of 40 bar for 8 min, well‐defined pattern structures with a line width of ≈330 nm and a separation of ≈413 nm are achieved. Meanwhile, hydrogen‐bonding‐directed multilayer films of poly(vinyl pyrrolidone) (PVPON)/poly(methyl acrylic acid) (PMAA) and poly(4‐vinylpyridine)/PAA can also be patterned in a similar way by RT‐NIL. The successful imprinting of these films originates from the high compressibility and fluidity of the layered polymeric films under high pressure.

SEM image of an imprinted (PAH/PAA)*20 film on silicon wafer.     

Nanoporous Network Channels from Self‐Assembled Triblock Copolymer Supramolecules

Supramolecular complexes of a poly(tert‐butoxystyrene)‐block‐polystyrene‐block‐poly(4‐vinylpyridine) triblock copolymers and less than stoichiometric amounts of pentadecylphenol (PDP) are shown to self‐assemble into a core–shell gyroid morphology with the core channels formed by the hydrogen‐bonded P4VP(PDP)complexes. After structure formation, PDP was removed using a simple washing procedure, resulting in well‐ordered nanoporous films that were used as templates for nickel plating.

     

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.

     

Novel One‐Step Route for Preparing Amphiphilic Block Copolymers of Styrene and N‐Isopropylacrylamide in a Microemulsion

Summary: Copolymerizations of St and NIPAM have been carried out through interfacial‐initiated microemulsion polymerization in a frozen state. FT‐IR and NMR spectroscopies confirm the occurrence of copolymerization between the two monomers. DSC analysis shows the existence of two glass transition temperatures of the resultant copolymers. The micellization of the copolymers is investigated by DLS and the temperature‐responsive behavior of the resultant micelles is observed. DSC and DLS results reveal the block feature of the obtained copolymers. Thus amphiphilic poly(styrene‐block‐N‐isopropylacrylamide) is prepared by a one‐step interfacial‐initiated microemulsion polymerization.

Hydrodynamic radius of the micellar particles formed by (left), and a typical DSC trace of (right), the poly(styrene‐block‐N‐isopropylacrylamide) prepared here.     

Micelles Formed by Cylindrical Brush‐Coil Block Copolymers

Summary: Amphiphilic cylindrical brush‐coil block copolymers consisting of a polystyrene coil and a cylindrical brush block with poly(acrylic acid) side chains are prepared by ATRP of t‐butylacrylate from a block comacroinitiator. Upon acidolysis of the poly(t‐butylacrylate), water‐soluble polymers were obtained that were observed to form micelles consisting of 4–5 block copolymers on average in aqueous solution. The star‐like nature of such micelles was clearly visualized by scanning force microscopy.

Schematic of coil‐cylindrical brush block copolymer PS‐b‐(PⁱBEMA‐g‐PAA), its AFM image clearly showing the main chain and the PAA corona of the cylindrical brush block.     

Functionalization of Crosslinked Vesicles by Co‐Self‐Assembly of a Gelable Diblock Copolymer and Mercaptosilane

Herein, a convenient and general method to simultaneously fix and functionalize polymeric vesicles with sulphydryl groups by the co‐self‐assembly of poly(ethylene oxide)‐block‐poly[3‐(triethoxysilyl)propyl methacrylate] (PEO‐b‐PTESPMA) and 3‐mercaptopropyltrialkoxysilane in an aqueous solution is reported. The presence of sulphydryl groups across the vesicle membrane has been confirmed by using an energy‐filtered technique during TEM analysis and by capturing Au nanoparticles.

     

Novel Photoactive Polymeric Multilayer Films Formed via Electrostatic Self‐Assembly

Summary: We demonstrate a novel approach for constructing photoactive multilayer films in which the aggregation of fluorescing molecules is effectively eliminated. In the films formed via a layer‐by‐layer electrostatic self‐assembly technique, the core‐shell amphiphilic copolymer, poly[(sodium 4‐styrenesulfonate)‐block‐vinylnaphthalene], was deposited. The isolated cores served as nanosized host sites for photoactive guest molecules (pyrene, perylene). The efficient energy transfer between polymeric chromophores and perylene molecules was observed.

AFM image of a nanostructured polymeric film prepared via a layer‐by‐layer technique and containing photoactive block copolymer poly[(sodium 4‐styrenesulfonate)‐block‐vinylnaphthalene]. Below is the representative height profile taken along the drawn line.     

Synthesis of a Novel Electroactive ABA Triblock Copolymer and its Spontaneous Self‐Assembly in Water

An electroactive triblock copolymer of poly(ethylene glycol) (PEG) and aniline pentamer (AP), PEG‐block‐AP‐block‐PEG (PAP), was synthesized via polycondensation in the presence of N,N'‐dicyclohexylcarbodiimide (DCC). The UV‐vis spectra and cyclic‐voltammograms (CV) spectra exhibited an excellent electroactivity of the triblock copolymer. The amphiphilic triblock copolymer self‐assembles spontaneously into uniform micellar aggregates when the triblock copolymer was added directly to the aqueous solution. The size of the aggregates can be changed with the oxidation state of the AP segment in the PAP copolymer and the aggregates were pH‐sensitive to the surrounding water solution, which provides a potential application in controlled drug release.

     

Synthesis and Surface Morphology of Tetraaniline‐block‐Poly(L‐lactate) Diblock Oligomers

Summary: Tetraaniline‐block‐poly(L ‐lactide) diblock oligomers are synthesized via ring‐opening polymerization. The diblock oligomers cast from an L ‐lactide selective solvent (chloroform) show spherical aggregates for the leucoemeraldine state, and ring‐like structures that are composed of much smaller spherical aggregates for the emeraldine state. The formation mechanisms of the two different surface morphologies are discussed in detail.

Surface morphology changes induced by oxidation of the aniline segment of tetraaniline‐block‐poly(L ‐lactate) and drying effects.     

Nano Grape Formation by isotactic‐Poly(methacrylic acid)‐block‐Poly(butyl acrylate)

A novel approach is employed to produce core–corona nanospheres, which introduces a stereoregular hydrophilic part to an amphiphilic block copolymer. The resultant morphology is reported using isotactic‐poly(methacrylic acid)‐block‐poly(butyl acrylate). Infrared spectroscopy revealed a supramolecular interaction, and X ray diffraction revealed the crystallization of the outer isotactic‐poly(methacrylic acid) part. The nanostructure, which looks like a nanosized ‘grape’, was formed when nanospheres and nanofibers coexisted simultaneously and partially fused.

     

Composite Worm‐Like Aggregates Formed from a Pair of Block‐Copolymers Containing Hydrogen‐Bonding Donor and Acceptor

Worm‐like aggregates with a PAA/P4VP complex core and a PEG/PNIPAM mixed shell were prepared in ethanol by the comicellization of poly(ethylene glycol)‐block‐poly(acrylic acid) (PEG‐b‐PAA) and poly(N‐isopropylacrylamide)‐block‐poly(4‐vinylpyridine) (PNIPAM‐b‐P4VP) through hydrogen‐bonding. The formed aggregates were studied by dynamic light scattering, static light scattering, ¹H NMR, and transmission electron microscopy. The length of worm‐like aggregates could be adjusted by changing the weight ratio of W(PNIPAM‐b‐P4VP)/W(PEG‐b‐PAA). When the ratio changed from 20 to 150%, the length changed from about 100 nm to several microns, and the diameter stayed almost unchanged at about 15 nm.

     

Synthesis and Self‐Assembly of Amphiphilic Diblock Copolymers using a Fluorescently Labeled N‐Alkoxyamine Initiator

Summary: An initiator for nitroxide mediated ‘living’ free radical polymerization was prepared with a fluorescent tag attached to the initiating alkyl radical terminus. This was used to synthesize amphiphilic poly(acrylic acid)‐block‐polystyrene diblock copolymers, which self assembled in a tetrahydrofuran/buffer solution to form structures that are visible by fluorescence.

     

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.

     

Diameter‐Dependence of the Morphology of PS‐b‐PMMA Nanorods Confined Within Ordered Porous Alumina Templates

Summary: Polystyrene‐block‐poly(methyl methacrylate) nanorods were prepared by wetting ordered porous alumina templates. We systematically investigated the diameter‐dependence of their morphologies by varying the pore diameters of the templates from 400 nm down to 25 nm. If the pore diameter exceeds the period of the block copolymer, the pores accommodate a non‐integer number of repeat periods. In case of smaller pores the occurrence of an ordered state could not be unambiguously verified.

TEM image of an ultra‐thin slice containing a cross‐section of a polystyrene‐block‐poly(methyl methacrylate) nanorod embedded in epoxy resin.     

Effect of Coordination on the Glucose‐Responsiveness of PEG‐b‐(PAA‐co‐PAAPBA) Micelles

Poly(ethylene glycol)‐block‐poly(acrylic acid) (PEG‐PAA) is modified by 3‐aminophenylboronic acid (APBA) with different modification degrees, such as PEG₁₁₄‐b‐(PAA_0.37‐co‐PAAPBA_0.63)₁₇₀, PEG₁₁₄‐b‐(PAA_0.23‐co‐PAAPBA_0.77)₁₇₀ and PEG₁₁₄‐b‐(PAA_0.02‐co‐PAAPBA_0.98)₁₇₀. Micelles self‐assembled from these three copolymers possess glucose‐responsiveness at varying pH values. Micelles self‐assembled from PEG₁₁₄‐b‐(PAA_0.37‐co‐PAAPBA_0.63)₁₇₀ have glucose‐responsiveness at the physiological pH (7.4), endowing them with potential applications in the treatment of diabetes. ¹¹B magic‐angle spinning nuclear magnetic resonance (¹¹B MAS NMR) analysis indicates that interactions between PAAPBA segments and PAA segments induce boron changes from the trigonal planar form to the tetrahedral form, resulting in glucose‐responsiveness of PEG₁₁₄‐b‐(PAA_0.37‐co‐PAAPBA_0.63)₁₇₀ micelles at pH 7.4.

     

Formation of Two Kinds of Hexagonally Arranged Structures in ABC Triblock Copolymer Thin Films Induced by a Strongly Selective Solvent Vapor

An order–order transition (OOT) in the sequence of a hexagonally arranged core–shell cylinder to a double‐hexagonally arranged dot in polystyrene‐block‐poly(butadiene)‐block‐poly(2‐vinylpyridine) (SBV) triblock copolymer thin films is reported to be induced upon exposure to a solvent vapor that is strongly selective for the two end blocks. These two kinds of hexagonally arranged structures could form when the film thickness is 44, 123, and 223 nm. When the film thickness is decreased to 13 nm, the ordered structure is absent. The sizes of the core–shell cylinder structures formed with the same annealing time in films of different thickness are compared to address the effects of film thickness on the phase structure. The mechanism is analyzed from the total surface area of the blocks and the effective interaction parameter in the solvent vapor.

     

Regioregular Poly(3‐hexylthiophene) in a Novel Conducting Amphiphilic Block Copolymer

Regioregular poly(3‐hexylthiophene) has been successfully incorporated into a novel amphiphilic block copolymer. The amphiphilic nature of poly(3‐hexylthiophene)‐block‐poly(acrylic acid) has been investigated using spectroscopic methods and has yielded solvatochromic behavior in several solvents of varying polarity. Evidence suggests that a supramolecular, long range ordering of block copolymer occurs in polar solvents, resulting in the formation of aggregates. Despite relatively large amounts of non‐conductive blocks, the poly(3‐hexylthiophene) diblock copolymer yields a high conductivity of 1 S · cm⁻¹, and atomic force microscopy shows the formation of a highly organized nanofibrilar morphology in the solid state.

     

Rheology and Physical Properties of Polyethylene/Polyethylene‐Ionomer Blends and their Clay Nanocomposites

Rheological and solid‐state physical properties of blends containing high‐density polyethylene (HDPE) and a polyampholyte derivative (PE‐g‐PA) are assessed along with their onium ion‐exchanged montmorillonite clay (NR‐MM) nanocomposites. Strong deviations from the log‐additivity rule of zero‐shear viscosity, combined with synergistic behavior in tensile moduli, are consistent with a multi‐phase blend morphology. While this affects clay dispersion in filled blends, PE‐g‐PA/HDPE based nanocomposites are shown to exhibit a favorable balance between material stiffness and ductility.