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.     

Orienting the Demixion of a Diblock‐copolymer Using 193 nm Interferometric Lithography for the Controlled Deposition of Nanoparticles

DUV interferometric lithography and diblock copolymer self‐organization have successfully been combined to provide a simple and highly collective nanopatterning technique enabling the organization of nanoparticles over several orders of magnitude, from nanometre to millimetre. The nanostructural changes at the surface of the polymer film after thermal annealing have been monitored by AFM and the process parameters optimized for obtaining a long‐range organization of the lamellar domains. In particular, the impact of the annealing conditions and geometric parameters of the substrate patterns have been investigated. The nanopatterns resulting from the lamellar demixion of (PS‐b‐MMA) were used for a controlled deposition of nanoparticles. The affinity of the hydrophobic particles for the PS block was demonstrated, opening new doors towards the preparation of high‐density arrays of nanoparticles with potential applications in data storage.

     

Ultrathin and Large‐area Macroporous Polymeric Membranes Formed Through Self‐assembly of Sub‐10 nm Elastic Nanoparticles

A variety of sub‐10 nm nanoparticles are successfully prepared by crosslinking of polystyrene‐b‐poly(1,3‐butadiene) (PS‐b‐PB) and polystyrene‐b‐poly(4‐vinyl pyridine) (PS‐b‐P4VP) block copolymer micelles and inverse micelles. Among them, the core‐crosslinked PS‐b‐PB micelles can self‐assemble into ultrathin (< 10 nm) macroporous (pore size <1 µm) membranes in a facile way, i.e., by simply drop‐coating the particle solution onto a mica surface. No continuous/porous membranes are produced from shell‐crosslinked PS‐b‐PB micelles and both forms of PS‐b‐P4VP micelles. This suggests that the unique structure of the block copolymer precursor, including the very flexible core‐forming block and the glassy corona‐forming block and the specific block length ratio, directly determines the formation of the macroporous membrane.

     

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.

     

Ordering Cylindrical Microdomains for Binary Blends of Block Copolymers with Graphoepitaxy

The morphology of a thin film was studied for a binary mixture of asymmetric PS‐b‐PMMA block copolymers on a flat silicon wafer coated with 50 nm thick silicon oxide. AFM and TEM reveal that the PMMA cylinders orient perpendicular to the substrate by tuning the film thickness. Furthermore, grating substrates with different width and depth are used to guide the alignment of the perpendicular cylinders. As a result, an array of highly ordered, hexagonally packed PMMA cylinders in the PS matrix with a domain spacing of less than 25 nm has been produced.

     

Formation of Polyolefin‐block‐polystyrene Block Copolymers on Phenoxyimine Catalysts

Summary: PE‐block‐PS and P(E‐co‐P)‐block‐PS block copolymers were synthesised via sequential monomer addition during homogeneous polymerisation on various phenoxyimine catalysts. One phenoxyimine catalyst was tailored to produce high molecular weight block copolymers containing both, polyolefin and polystyrene segments. According to chromatographic analysis and TEM morphology studies, blends of block copolymers and PE homopolymers [or P(E‐co‐P), respectively] were formed. The direct olefin/styrene block copolymer synthesis on phenoxyimine catalysts represents an attractive, new one‐pot route to styrenic block copolymers which are commercially prepared by anionic styrene/diene block copolymerisation followed by hydrogenation.

     

A New Crystal Form,Polymorphism, and Multi‐Morphology in Biodegradable Poly(3‐hydroxypropionate)

Summary: A new crystal morphology (δ form) of poly(3‐hydroxypropionate) (PHP) is found in cast and melt‐crystallized PHPs with low molecular weight, in which the PHP chains possibly adopt a 2₁ helix rather than the trans conformation found in the β or γ form. The fusion temperature‐ and the crystallization temperature‐dependent polymorphism are responsible for the dual morphologies and the unique growth kinetics of spherulites in the melt‐crystallized PHPs.

a) A dual‐morphology developed at 70 °C in PHP films after melting at 117 °C and b) that formed during cooling at a rate of 1 °C · min⁻¹ from 130 °C.     

Cu(II)‐Mediated ATRP of MMA by Using a Novel Tetradentate Amine Ligand with Oligo(ethylene glycol) Pendant Groups

A novel tetradentate amine ligand namely N,N,N′,N″,N‴;,N‴;‐hexaoligo(ethylene glycol) triethylenetetramine (HOEGTETA) was employed in the homogenous ATRP of MMA in anisole using CuBr and CuBr₂ as the catalyst and ethyl 2‐bromoisobutyrate (EBiB) as an initiator. The effect of the polymerization temperature and the various ratios of Cu(I) to Cu(II) were investigated in detail. Moreover, we demonstrated the ATRP of MMA by using only Cu(II) in the absence of any free radical initiator, reducing agent, or air. The ATRP of MMA with the use of only Cu(II) and HOEGTETA or N,N,N′,N″,N″‐pentamethyldiethylenetriamine (PMDETA) resulted in well‐defined PMMA.

     

Strain‐Induced Phase Morphology in Melt Drawn Ultrathin Highly Oriented Block Copolymer Films

A strain‐induced microphase morphology has been established by the melt drawing process in a high molecular weight asymmetric polystyrene‐block‐poly(vinyl‐2‐pyridine) (PS‐b‐P2VP) diblock copolymer. For the first time to the best knowledge of the authors, the melt drawing process has been applied to block copolymers to produce free‐standing, ultrathin block copolymer films with a thickness of ≈100 nm. Intriguingly, during the melt drawing of the polymer a global strain‐induced unidirectional order of the microphase separated needle‐like domains of the block copolymer was generated. This morphology consists of a PS matrix with embedded highly oriented P2VP needle‐like domains oriented parallel to the drawing direction. The needle‐like morphology is explained by a simplified extended chain model of the diblock copolymer chains. Annealing of the films leads to a transition from the strain‐induced needle‐like morphology toward the quasi‐equilibrium sphere‐like morphology.

     

Phosphorus Ligands for Iron(III)‐Mediated Atom Transfer Radical Polymerization of Methyl Methacrylate

The iron(III)‐catalyzed atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA) was successfully employed using tributylphosphine (TBP) and trimethylphosphite (TMP) as ligands in the absence of a reducing agent. The effects of solvent and initiator on polymerization of MMA were investigated. Most of the polymerizations with these ligands were well controlled with a linear increase in the number average molecular weights ( ) versus conversion and relatively low molecular weight distribution ( = 1.2–1.4) throughout the reactions, and the measured weights matched with the predicted values. The ethyl 2‐bromoisobutyrate (EBriB) initiated ATRP of MMA with the FeBr₃/TBP or FeBr₃/TMP catalytic system was better controlled in toluene than in the other solvents used in this study at 80 °C.

     

Effect of Cyclization of Polystyrene/Polyisoprene Block Copolymers on Their Micellar Morphology

Micelles made from linear polystyrene‐block‐polyisoprene (PS/PI) in decane are spherical. The differences in the structure of micelles made from linear and cyclic PS/PI were investigated using small‐angle X‐ray scattering at rest and under shear flow. The effect of shear revealed that micelles made from cyclic copolymer chains have an elongated shape, which was confirmed by transmission electron microscopy. The cyclization of diblock copolymer chains is thus a new method to control the micellar morphology.

     

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.     

Synthesis of Well‐Defined Figure‐of‐Eight‐Shaped Polymers by a Combination of ATRP and Click Chemistry

Well‐defined figure‐of‐eight‐shaped (8‐shaped) polystyrene (PS) with controlled molecular weight and narrow polydispersities has been prepared by the combination of atom transfer radical polymerization (ATRP) and click chemistry. The synthesis involves two steps: 1) Preparation of a linear tetrafunctional PS with two azido groups, one at each end of the polymer chain, and two acetylene groups at the middle of the chain. 2) Intramolecular cyclization of the linear tetrafunctional PS at a very low concentration by a click reaction to produce the 8‐shaped polystyrenes. The resulting intermediates and the target polymers were characterized by ¹H NMR and FT‐IR spectroscopy, and gel permeation chromatography. The glass transition temperatures (T_gs) were determined by differential scanning calorimetry and it was found that the decrease in chain mobility by cyclization resulted in higher T_gs for 8‐shaped polystyrenes as compared to their corresponding precursors.

     

Surface Morphology Evolution of a Thin Polymeric Supramolecular Film by Tuning Interactions

Summary: A polymeric supramolecule consisting of symmetric polystyrene‐block‐poly(4‐vinylpyridine) (PS‐b‐P4VP), dodecylbenzenesulfonic acid (DBSA), and 3‐pentadecylphenol (PDP) was formed by proton transfer and hydrogen bonding. The surface morphology of a thin film of the polymeric supramolecule has been investigated. The spherical PS microdomains embedded in a P4VP(DBSA)_1.0(PDP)_1.0 matrix are observed for the as‐cast film because the weight fraction, f_comb, of the P4VP(DBSA)_1.0(PDP)_1.0 blocks is much higher than that of PS as a result of the non‐covalent interactions of P4VP and DBSA and DBSA and PDP. Upon annealing the PS‐b‐P4VP(1:1)(DBSA)_1.0(PDP)_1.0 film at high temperatures, the hydrogen bonding between the DBSA and PDP diminishes, which leads to a change of overall morphology from an ordered sphere to a pitted structure.

AFM topographic image of a PS‐b‐P4VP(1:1)(DBSA)_1.0(PDP)_1.0 thin film.     

Improved PEDOT Conductivity via Suppression of Crystallite Formation in Fe(III) Tosylate During Vapor Phase Polymerization

Vapor phase polymerization was used to synthesize high conductivity poly(3,4‐ethylenedioxyphenylene) (PEDOT). The monomer is presented to an oxidant‐rich substrate in vapor form and even for short polymerization times, 10–30 min, Fe(III) tosylate has a propensity for water absorption leading to crystal formation. Poor oxidant treatment before polymerization or high humidity during polymerization can create holes in the PEDOT film decreasing its conductivity. The addition of an amphiphilic copolymer poly(ethylene glycol)‐ran‐poly(propylene glycol) suppresses crystal growth allowing better film formation. The humidity level during synthesis was optimized at 35% relative humidity (RH), producing a conductivity of 761 S · cm⁻¹. Additionally, the copolymer extends the RH range that is tolerable for polymer synthesis.

     

Advancing the Solid State Properties of Metallo‐Supramolecular Materials: Poly(ε‐caprolactone) Modified π‐Conjugated Bis(terpyridine)s and their Zn(II) Based Metallo‐Polymers

A set of rigid π‐conjugated bis(terpyridine) macroligands with poly(ε‐caprolactone) (pCL) on their side chains was synthesized and investigated. The introduced pCL chains gave rise to enhanced processability and film‐forming properties of the materials. Blue photoluminescence with high quantum yields was observed in dilute solution and in the solid state, indicating that intermolecular aggregation of the π‐conjugated systems was effectively suppressed. The macroligands were further used for coordination with zinc(II) ions leading to new metallo‐polymers with high solubility, improved film‐forming behavior and promising photophysical properties with respect to potential OLED applications.

     

One‐Pot Fabrication of Supramolecular Polymer Particles via Situ Polymerization Stringed Assembly of a Two‐Monomer Microemulsion

Summary: A novel method, situ polymerization stringed assembly (SPSA), is proposed to prepare stable solid or hollow supramolecular polymer particles, which are assembled by numerous nanoparticles. By this method, the fabrication of primary nanoparticles (poly(methyl methacrylate), PMMA), the linkers (polyvinylpyrrolidone, PVP, chains) between the nanoparticles, and the final assembled solid or hollow particles could be achieved in just one‐pot by methyl methacrylate (MMA)/N‐vinylpyrrolidone (NVP) microemulsion polymerization under UV irradiation. The structures of the supramolecular particles can be changed from solid to hollow by tuning the mass ratio of MMA/NVP in the microemulsion. AFM, TEM, and SEM experiments are performed to identify the results.

AFM image of the PMMA/PVP solid particles obtained from the photopolymerization of the microemulsion containing 20 wt.‐% MMA, 10 wt.‐% NVP, and 5 × 10⁻² wt.‐% BP.     

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.

     

Chemoenzymatic Synthesis of a Multivalent Aminoglycoside

A polymeric aminoglycoside was prepared by a facile chemoenzymatic reaction. Boc‐protected aminoglycoside, amikacin, was chemoselectively esterified with divinyl sebacate at a hydroxyl group in the C6″ position by protease from Bacillus subtilis. The resulting 3,6′,3″,4?‐tetra‐N‐Boc‐6″‐O‐vinyl sebacate was copolymerized with maltitol 6‐vinyl sebacate to yield a polymeric amikacin. The polymeric amikacin showed a modest inhibitory effect on in vitro protein synthesis, and a little antibiotic activity in minimum inhibitory concentration (MIC) assay in the presence of protease.

The synthesis of Boc‐protected amikacin ester by an enzyme‐catalyzed (protease) esterification.