Formation of Integral Asymmetric Membranes of AB Diblock and ABC Triblock Copolymers by Phase Inversion

The formation of integral asymmetric membranes from ABC triblock terpolymers by non‐solvent‐induced phase separation is shown. They are compared with the AB diblock copolymer precursors. Triblock terpolymers of polystyrene‐block‐poly(2‐vinylpyridine)‐block‐poly(ethylene oxide) (PS‐b‐P2VP‐b‐PEO) with two compositions are investigated. The third block supports the formation of a membrane in a case, where the corresponding diblock copolymer does not form a good membrane. In addition, the hydrophilicity is increased by the third block and due to the hydroxyl group the possibility of post‐functionalization is given. The morphologies are imaged by scanning electron microscopy. The influence of the PEO on the membrane properties is analyzed by water flux, retention, and dynamic contact angle measurements.

     

Synthesis of a Novel ABC Triblock Copolymer with a Rigid‐Rod Block via Atom Transfer Radical Polymerization

Summary: A novel ABC triblock copolymer with a rigid‐rod block was synthesized by atom transfer radical polymerization (ATRP). First, a poly(ethylene oxide) (PEO)‐Br macroinitiator was synthesized by esterification of PEO with 2‐bromoisobutyryl bromide, which was subsequently used in the preparation of a poly(ethylene oxide)‐block‐poly(methyl methacrylate) (PEO‐b‐PMMA) diblock copolymer by ATRP. A poly(ethylene oxide)‐block‐poly(methyl methacrylate)‐block‐poly{2,5‐bis[(4‐methoxyphenyl)oxycarbonyl]styrene} (PEO‐b‐PMMA‐b‐PMPCS) triblock copolymer was then synthesized by ATRP using PEO‐b‐PMMA as a macroinitiator.

ABC triblock copolymer with a rigid‐rod block.     

Electromechanical Response of Nanostructured Polymer Systems with no Mechanical Pre‐Strain

A dielectric elastomer derived from a polystyrene‐block‐poly(ethylene‐co‐butylene)‐block‐polystyrene triblock copolymer swollen with a midblock‐selective solvent is reported to show promise as a nanostructured organic actuator requiring no pre‐strain. This might provide an attractive alternative to conventional acrylic, siloxane, and polyurethane elastomers since the electromechanical properties are composition‐tunable.

     

“Sandglass”‐Shaped Self‐Assembly of Coil–rod–coil Triblock Copolymer Containing Rigid Aniline‐Pentamer

The amphiphilic PEG_{1 500}‐b‐EM AP‐b‐PEG_{1 500} (EM PAP) triblock copolymer of poly(ethylene glycol) (PEG) and emeraldine aniline‐pentamer (EM AP) in its concentrated solution can self‐assemble into a special shape like “sandglass”, as observed by transmission electron microscopy (TEM), field emission scanning electron microscopy (ESEM) and atomic force microscopy (AFM). This “sandglass”‐shaped assembly is composed of several “rods” aggregated in the middle, with every “rod” being about 8 µm in length and 300 nm in diameter. We conclude that the special “sandglass”‐shaped assembly may come into being because of the inducement effect of the crystallization of EM AP segments, by studying electron diffraction (ED) results and wide‐angle X‐ray diffusion (WAXD) characterization of the EM PAP triblock copolymer.

     

Synthesis of Amphiphilic ABC Triblock Copolymers with PEO as the Middle Block

Summary: Stepwise anionic polymerization, catalytic hydrogenation, and atom transfer radical polymerization were performed to synthesize an amphiphilic ABC triblock copolymer, poly(ethylene‐alt‐propylene)‐block‐poly(ethylene oxide)‐block‐poly(hexyl methacrylate) (PEP‐b‐PEO‐b‐PHMA), with hydrophilic PEO as the middle block. The resulting block copolymers have well‐defined molecular weights and narrow molecular weight distributions as revealed by ¹H NMR spectroscopy and gel permeation chromatography.

GPC chromatograms of an ABC triblock copolymer, PEP‐b‐PEO‐b‐PHMA, and its intermediate precursors exhibiting narrow polydispersities.     

Synthesis of Well‐Defined Rod‐Coil‐Rod Polyhexylisocyanate‐block‐polystyrene‐block‐polyhexylisocyanate via One‐Pot Anionic Polymerization

A rod‐coil‐rod block copolymer, polyhexylisocyanate‐block‐polystyrene‐block‐polyhexylisocyanate, of controlled molecular weight was synthesized quantitatively via living anionic polymerization using potassium naphthalenide in the presence of sodium tetraphenylborate. The use of K⁺ as the counterion for the polymerization of styrene, and Na⁺ (NaBPh₄) for the polymerization of isocyanate leads to the formation of a well‐controlled novel triblock copolymer.

     

Effect of Microstructures on the Phase Transition Behavior of P(CL‐GL)‐PEG‐P(CL‐GL) Triblock Copolymer Aqueous Solutions

Amphiphilic poly[(ε‐caprolactone)‐co‐glycolide]‐block‐poly(ethylene glycol)‐block‐poly[(ε‐caprolactone)‐co‐glycolide) [P(CL‐GL)‐PEG‐P(CL‐GL)] triblock copolymers with different average lengths of caproyl sequences (L_CL) were synthesized by ring‐opening polymerization at different temperatures. A 25% aqueous solution of the copolymer with L_CL = 11.0 formed a gel, owing to strong crystallinity‐induced hydrophobicity at low temperature, and underwent a gel‐sol transition (UCST behavior) when the temperature was increased to 40 °C. In contrast, the solution of copolymer with L_CL = 6.7 underwent a sol‐gel transition (LCST behavior) due to micelle aggregation. However, a clear sol‐turbid sol phase transition was observed for the copolymer with more random microstructures (L_CL = 5.2).

     

Fabrication of Poly(L‐lactide)‐block‐Poly(ethylene glycol)‐block‐Poly(L‐lactide) Triblock Copolymer Thin Films with Nanochannels: An AFM Study

This paper aims to report the fabrication of biodegradable thin films with micro‐domains of cylindrical nanochannels through the solvent‐induced microphase separation of poly(L ‐lactide)‐block‐poly(ethylene glycol)‐block‐poly(L ‐lactide) (PLA‐b‐PEG‐b‐PLA) triblock copolymers with different block ratios. In our experimental scope, an increase in each of the block lengths of the PLA and PEG blocks led to both a variation in the average number density (146 to 32 per 100 µm²) and the size of the micro‐domains (140 to 427 nm). Analyses by atomic force microscopy (AFM) and fluorescence microscopy indicated that the hydrophilic PEG nanochannels were dispersed in the PLA matrix of the PLA‐b‐PEG‐b‐PLA films. We demonstrated that the micro‐domain morphology could be controlled not only by the block length of PEG, but also by the solvent evaporation conditions.

     

Self‐Assembled Micelles Based on PEG‐Polypeptide Hybrid Copolymers for Drug Delivery

A series of amphiphilic poly(L ‐leucine)‐block‐poly(ethylene glycol)‐block‐poly(L ‐leucine) (PLL‐PEG‐PLL) hybrid triblock copolymers have been synthesized. All the blocks in this system have good biocompatibility and low toxicity. The PLL‐PEG‐PLL copolymers could self‐assemble into micelles with PLL blocks as the hydrophobic core and PEG blocks as the hydrophilic shell, which were characterized by FT‐IR, ¹H NMR, and transmission electron microscopy analysis. The critical micellar concentration of the copolymer was 95.0 mg · L⁻¹. The circular dichroism spectrum shows that the PLL segments adopt a unique α‐helical conformation, which is found to play an important role in controlling the drug release rate. The drug release could be effectively sustained by encapsulation in the micelles. The copolymers may have potential applications in drug delivery.

     

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.

     

Polyoxazoline Thermoresponsive Micelles as Radionuclide Delivery Systems

Thermoresponsive polymer micelles are promising drug and radionuclide carriers with a strong passive targeting effect into solid tumors. We have synthesized ABA triblock copolymers poly[2‐methyl‐2‐oxazoline‐block‐(2‐isopropyl‐2‐oxazoline‐co‐2‐butyl‐2‐oxazoline)‐block‐2‐methyl‐2‐oxazoline]. These polymers are molecularly dissolved in aqueous millieu below the cloud point temperature (CPT) of the thermoresponsive central block and above CPT form polymer micelles at CMC 5–10 × 10^?5 g · mL^?1 with diameter ≈200 nm. The phenolic moiety introduced into the copolymer allowed radionuclide labeling with iodine‐125 ongoing in good yield with sufficient in vitro stability under model conditions.

     

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.

     

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).     

Liquid Crystalline Period Variations in Self‐Assembled Block Copolypeptides–Surfactant Ionic Complexes

We investigate the complexation of ampholytic poly(N‐isopropylacylamide)‐block‐poly‐ (L ‐glutamic acid)‐block‐poly(L ‐lysine) (PNiPAM‐b‐PLG‐b‐PLLys) triblock copolymers and PNiPAM‐block‐(PLG‐co‐PLLys) diblock copolymers with counter charged anionic and cationic surfactants. Both triblock and diblock copolymers are able to selectively form complexes through either L ‐glutamic acid–cationic surfactant or L ‐lysine–anionic surfactant ionic pairs, depending on the protonated or deprotonated states of the ampholytic peptide units. The complexes show ordering at multiple length scales: i) the block copolymer length scale (10¹ nm), ii) the liquid crystalline length scale (10⁰ nm), and, iii) the peptidic secondary structures length scale (10⁰ nm). We show that the liquid crystalline period can be tuned by varying the random/block copolypeptide architectures and the composition of the ampholytic amino acid species.

     

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.

     

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.     

Synthesis of Poly(glycidyl methacrylate)‐block‐Poly(pentafluorostyrene) by RAFT: Precursor to Novel Amphiphilic Poly(glyceryl methacrylate)‐block‐Poly(pentafluorostyrene)

Poly(glycidyl methacrylate) (PGMA) was synthesized by the RAFT method in the presence of 2‐cyanoprop‐2‐yl dithiobenzoate (CPDB) chain transfer agent using different [GMA]/[CPDB] molar ratios. The living radical polymerization resulted in controlled molecular weights and narrow polydispersity indices (PDI) of ≈1.1. The polymerization of pentafluorostyrene (PFS) with PGMA as the macro‐RAFT agent yielded narrow PDIs of ≤1.2 at 60 °C and ≤1.5 at 80 °C. The epoxy groups of the PGMA block were hydrolyzed to obtain novel amphiphilic copolymer, poly(glyceryl methacrylate)‐block‐poly(pentafluorostyrene) [PGMA(OH)‐b‐PPFS]. The PGMA epoxy group hydrolysis was confirmed by ¹H NMR and FTIR spectroscopy. DSC investigation revealed that the PGMA‐b‐PPFS polymer was amorphous while the PGMA(OH)‐b‐PPFS displayed a high degree of crystallinity.

     

A Novel ABC Triblock Copolymer with Very Low Surface Energy: Poly(dimethylsiloxane)‐block‐Poly(methyl methacrylate)‐block‐Poly(2,2,3,3,4,4,4‐heptafluorobutyl methacrylate)

Poly(dimethylsiloxane)‐block‐poly(methyl methacrylate)‐block‐poly(2,2,3,3,4,4,4‐heptafluorobutyl methacrylate) was successfully synthesized via ATRP. The chemical composition and structure of the copolymer was characterized by NMR and FT‐IR spectroscopy and molecular weight measurement. Gel permeation chromatography was used to study the molecular weight distribution of the triblock copolymer. The surface properties of the resulting copolymer were investigated. The effects of fluorine content and bulk structure on surface energy were investigated by static water contact angle measurements. Surface composition was studied by XPS.

     

Ring‐Opening Polymerization of ε‐Caprolactone by Poly(ethylene glycol) by an Activated Monomer Mechanism

Summary: The polymerization of ε‐caprolactone (CL) in the presence of HCl · Et₂O by an activated monomer mechanism was performed to synthesize diblock or triblock copolymers composed of poly(ethylene glycol) (PEG) and poly(ε‐caprolactone) (PCL). The obtained PCLs had molecular weights close to the theoretical values calculated from the CL to PEG molar ratios and exibited monomodal GPC curves. We successfully prepared PEG and PCL block copolymers by a metal‐free method.

The non‐metal catalyzed living ring‐opening polymerisation of ε‐caprolactone by PEG.     

From Nanodot to Nanowire: Hybrid Au/Titania Nanoarrays by Block Copolymer Templates

A simple scheme to fabricate 2‐D arrays of Au/titania hybrid nanopatterns is presented, using polystyrene‐block‐poly(ethylene oxide) diblock copolymer (PS‐b‐PEO) as templates coupled with sol–gel chemistry. Both the functionalized Au nanoparticles (NPs) and titania precursors are selectively incorporated into the PEO domain. A series of morphologies ranging from nanodot to nanowire arrays is formed and the mechanism of morphological evolution is discussed. Such hybrid films exhibit characteristic localized surface plasmon resonance bands originating from the coupling between neighboring Au NPs spatially located in a controlled manner.