Self‐Assembly of Carbon Nanotubes Modified by Amphiphilic Block Polymers in Selective Solvent

Block copolymers of polystyrene and poly(tert‐butyl methyacrylate) were prepared by ATRP. Halogen atoms at the chain ends were transformed into azide groups to obtain  N₃ terminated block copolymers, which were connected to the surface of multi‐walled carbon nanotubes (MWNTs) by reacting  N₃ with MWNT's surface. Amphiphilic diblock copolymer modified MWNTs were obtained after PtBMA blocks were hydrolyzed to polymethyacrylic acid (PMAA). Results showed that the amphiphilic diblock copolymer was grafted onto MWNTs by covalent bonds. TEM showed that they formed self‐assembly structures by hydrophilic/hydrophobic interaction in good solvents. As the block length of PMAA increased, the self‐assembly structures of amphiphilic MWNTs became increasingly ordered and uniform.

     

Crystallization and Ring‐Banded Spherulite Morphology of Poly(ethylene oxide)‐block‐Poly(ε‐caprolactone) Diblock Copolymer

Summary: The crystallization behavior of crystalline‐crystalline diblock copolymer containing poly(ethylene oxide) (PEO) and poly(ε‐caprolactone) (PCL), in which the weight fraction of PCL is 0.815, has been studied via differential scanning calorimeter (DSC), wide‐angle X‐ray diffraction (WAXD), and polarized optical microscopy (POM). DSC and WAXD indicated that both PEO and PCL blocks crystallize in the block copolymer. POM revealed a ring‐banded spherulite morphology for the PEO‐b‐PCL diblock copolymer.

DSC heating curve for the PEO‐b‐PCL block copolymer.     

Synthesis and Characterization of Amphiphilic Poly(ethylene oxide)‐block‐poly(hexyl methacrylate) Copolymers

We describe the preparation of amphiphilic diblock copolymers made of poly(ethylene oxide) (PEO) and poly(hexyl methacrylate) (PHMA) synthesized by anionic polymerization of ethylene oxide and subsequent atom transfer radical polymerization (ATRP) of hexyl methacrylate (HMA). The first block, PEO, is prepared by anionic polymerization of ethylene oxide in tetrahydrofuran. End capping is achieved by treatment of living PEO chain ends with 2‐bromoisobutyryl bromide to yield a macroinitiator for ATRP. The second block is added by polymerization of HMA, using the PEO macroinitiator in the presence of dibromobis(triphenylphosphine) nickel(II), NiBr₂(PPh₃)₂, as the catalyst. Kinetics studies reveal absence of termination consistent with controlled polymerization of HMA. GPC data show low polydispersities of the corresponding diblock copolymers. The microdomain structure of selected PEO‐block‐PHMA block copolymers is investigated by small angle X‐ray scattering experiments, revealing behavior expected from known diblock copolymer phase diagrams.

SAXS diffractograms of PEO‐block‐PHMA diblock copolymers with 16, 44, 68 wt.‐% PEO showing spherical (A), cylindrical (B), and lamellae (C) morphologies, respectively.     

Synthesis,Characterization, and Thermal Properties of Block Copolymers Containing Poly(styrene‐co‐4‐vinylpyridine) and Poly(styrene‐co‐butyl acrylate) by Controlled Radical Polymerization

Radical polymerization of styrene and mixtures of styrene and 4‐vinylpyridine was performed in the presence of 2,2,6,6‐tetramethylpiperidine‐N‐oxyl (TEMPO) producing polymers with controlled molecular weights and molecular weight distributions. The living nature of these polymers was confirmed by using them as macroinitiators in the block copolymerization of styrene and butyl acrylate. The thermal properties of the synthesized statistical diblock copolymers measured by differential scanning calorimetry indicated that a phase‐separated morphology was exhibited in most of the block copolymers. The results were confirmed by transmission electron microscopy (TEM) and small angle X‐ray scattering (SAXS) showing microphase‐separated morphology as is known for homo A‐B diblock polymers.

SAXS of a block copolymer synthesized from S/V 70:30 macroinitiators (03) with one detected T_g.     

Pyrene End‐Labeled Diblock Glycopolymers: Synthesis and Aggregation

Summary: A pyrene end‐labeled amphiphilic block copolymer, poly(ε‐caprolactone)‐block‐poly[6‐O‐(4‐vinylbenzyl)‐D ‐galactose] (Py‐PCL‐b‐PVBG), was synthesized by a four‐step method. The aggregation behavior of the diblock copolymer in solution was studied by monitoring the fluorescence of pyrene. TEM measurements revealed that the aggregates obtained by first dissolving the copolymer in N,N‐dimethylformamide (DMF), followed by the addition of water, were primarily spheres with the PCL blocks in the core. The PVBG corona was then crosslinked with glutaraldehyde. Final removal of the PCL core was accomplished by degradation under basic conditions, which resulted in the formation of hollow glycopolymer nanospheres.

Structure of poly(ε‐caprolactone)‐block‐poly[6‐O‐(4‐vinylbenzyl)‐D ‐galactose].     

Amphiphilic Block Copolymers Containing Regioregular Poly(3‐hexylthiophene) and Poly(2‐ethyl‐2‐oxazoline)

Poly(3‐hexylthiophene)‐block‐poly(2‐ethyl‐2‐oxazoline) amphiphilic rod–coil diblock copolymers have been synthesized by a combination of Grignard metathesis (GRIM) and ring‐opening cationic polymerization. Diblock copolymers containing 5, 15, and 30 mol‐% poly(2‐ethyl‐2‐oxazoline) have been synthesized and characterized. The synthesized rod–coil block copolymers display nanofibrillar morphology where the density of the nanofibrills is dependent on the concentration of the poly(2‐ethyl‐2‐oxazoline) coil segment. The conductivity of the diblock copolymers was lowered from 200 to 35 S · cm^?1 with an increase in the content of the insulating poly(2‐ethyl‐2‐oxazoline) block. By contrast, the field‐effect mobility decreased by 2–3 orders of magnitude upon the incorporation of the poly(2‐ethyl‐2‐oxazoline) insulating segment.

     

Syntheses and Specific Interactions of Poly(ε‐caprolactone)‐block‐poly(vinyl phenol) Copolymers Obtained via a Combination of Ring‐Opening and Atom‐Transfer Radical Polymerizations

Summary: A series of PCL‐b‐PVPh diblock copolymers were prepared through combinations of ring‐opening and atom‐transfer radical polymerizations of ε‐caprolactone and 4‐acetoxystyrene, and subsequent selective hydrolysis of the acetyl protective group. This PCL‐b‐PVPh diblock copolymer shows a single glass transition temperature over the entire composition range, indicating that this copolymer is able to form a miscible amorphous phase due to the formation of intermolecular hydrogen bonding between the hydroxyl of PVPh and the carbonyl of PCL. In addition, DSC analyses also indicated that the PCL‐b‐PVPh diblock copolymers have higher glass transition temperatures than their corresponding PCL/PVPh blends. FT‐IR was used to study the hydrogen‐bonding interaction between the PVPh hydroxyl group and the PCL carbonyl group at various compositions.

FT‐IR spectra in the 1 680–1 780 cm^?1 for PCL‐b‐PVPh copolymers with various PVPh contents.     

A Poly(vinyl alcohol)‐graft‐Copolyester: Synthesis of a Novel Graft Copolymer Containing Adamantane Moieties as Guest for Cyclodextrin

A novel graft copolymer is synthesized from commercially available poly(vinyl alcohol) using ring‐opening polymerization. For the polymerization reaction of novel brush‐like poly(vinyl alcohol)‐graft‐poly(?‐caprolactone‐co‐(3‐/7‐(prop‐2‐ynyl)oxepan‐2‐one) 5 Sn(Oct)₂ is used as a catalyst. The formation of the graft copolymer is confirmed by ¹H NMR, ¹³C NMR, and Fourier transform infrared (FTIR) spectroscopy. Furthermore, the modification of the novel synthesized graft copolymer via a “click” reaction to implement adamantane groups is described. The success of the “click” reaction is proven by ¹H NMR spectroscopy and visualized by decomplexation of cyclodextrin with included phenolphthalein.

     

Diblock Copolymers with Azobenzene Side‐Groups and Polystyrene Matrix: Synthesis,Characterization and Photoaddressing

Summary: Diblock copolymers with a photoaddressable dispersed phase containing p‐methoxy substituted azobenzene side groups and a polystyrene matrix were synthesized and characterized. The block copolymers were prepared by a sequential living anionic polymerization of butadiene and styrene. The poly(1,2‐butadiene) segment was hydroborated and the hydroxy‐functions converted by a polymeranalogous reaction with the azo chromophore as side groups. The block copolymers were synthesized with different compositions by varying the length of the polystyrene segment and the length of the functionalized segment in order to obtain different morphologies. In this paper, for the first time a comparison of the cis‐trans photo‐isomerization behavior and photoaddressing with respect to different morphologies of the block copolymers is presented. To complete the comparison, the corresponding homopolymer and a statistical copolymer were also synthesized and investigated. A different photoaddressing behavior between homopolymer, statistical copolymer and the block copolymers was observed. One principal difference and advantage for photo addressable block copolymers is the lack of a formation of surface gratings which occurs in homopolymers and statistical copolymers.

TEM of a poly(1,2‐butadiene)‐block‐polystyrene copolymer containing azobenzene side‐groups.     

Pyrene Containing Polymers for the Non‐Covalent Functionalization of Carbon Nanotubes

Pyrene containing diblock copolymers based on poly(methyl methacrylate) were synthesized and investigated regarding their adsorption on carbon nanotubes (CNT). The pyrene units were introduced using a reactive ester monomer for the build up of the second block which later on was reacted polymer‐analogously with amine functionalized pyrene derivatives. As we started from the same reactive ester intermediate, full block length identity is given. We varied the length of the anchor block to find an optimal block length and used pyren‐1‐yl‐methylamine as well as 4‐pyren‐1‐yl‐butylamine as anchor units. For both anchor units a maximal adsorption was found for 13 and 20 anchor units, respectively. The absolute adsorption was best for the 4‐pyren‐1‐yl‐butylamine anchor units as the longer spacer enhances the mobility of the anchor unit. The dispersion diagram of CNTs and diblock copolymer in terms of dispersion stability was investigated and a stable dispersion of 2.5 mg · ml^?1 CNTs in THF was found.

     

Rod‐Length Dependent Aggregation in a Series of Oligo(p‐benzamide)‐Block‐Poly(ethylene glycol) Rod‐Coil Copolymers

Summary: The synthesis of a series of rod‐coil diblock copolymers with flexible poly(ethylene oxide) chains ( = 5 000 g · mol⁻¹) and rod blocks consisting of monodisperse oligo(p‐benzamide)s is described. The formation of defined supramolecular aggregates in solution as well as the solid state has been analyzed. The length of the oligo(p‐benzamide)s has been systematically varied from n = 1 to 7 units. The influence of n on aggregation in chloroform and aqueous solution was investigated by GPC as well as UV‐vis spectroscopy. A critical aggregation length was found for chloroform (n = 5) and water (n = 4), below which no aggregation is observed under otherwise identical experimental conditions. Aggregation of the polymers in chloroform solution can be chemically reversed by the addition of PCl₅, resulting in conversion of the aromatic amides into imidoyl chlorides. Such amide‐protected block copolymers show no aggregation in NMR and GPC experiments. Imidoyl chloride formation was shown to be reversible, i.e., addition of water regenerated the oligo(p‐benzamide) blocks.

Conversion of aramide block copolymer into molecularly dissolved form using PCl₅.     

Block Copolymers from Organomodified Siloxane‐Containing Macroinitiators by Atom Transfer Radical Polymerization

Alternating copolymers of 1,3‐diisopropenylbenzene and 1,1,3,3‐tetramethyldisiloxane were synthesized by hydrosilylation–polyaddition. These linear copolymers were functionalized at both ends with 2‐bromoisobutyryl or benzyl chloride moieties. Subsequently, the obtained organomodified siloxane‐containing macroinitiators were successfully used for the preparation of ABA‐type block copolymers by atom transfer radical polymerization (ATRP) of styrene and tert‐butyl acrylate. The high chain‐end functionality of the macroinitiators was confirmed by ¹H NMR analysis of the macroinitiators and GPC measurements of the obtained ABA‐type block copolymers. The macroinitiator peaks disappeared in GPC traces after ATRP, and the obtained block copolymers showed a significantly narrower molecular‐weight distribution than the macroinitiators.

Synthesis of ABA‐type block copolymers by means of ATRP using organomodified siloxane‐containing, benzyl chloride functionalized macroinitiators.     

Terpyridine‐Terminated Homo and Diblock Copolymer LEGO Units by Nitroxide‐Mediated Radical Polymerization

Summary: Novel block copolymers were synthesized in a controlled fashion by nitroxide‐mediated radical polymerization starting from a terpyridine‐modified alkoxyamine. An important feature for controlling the efficiency of the polymerization is the presence of excess nitroxide, responsible for the initial rate of deactivation, which eventually leads to a decrease of the polydispersity indices of the desired block copolymer. The materials obtained were characterized by means of ¹H NMR, UV‐vis spectroscopy, and GPC. The complexation of the terpyridine ligands resulted in the formation of A‐B‐[Ru]‐C, A‐B‐[Ru]‐B‐A, and A‐B‐[Fe]‐B‐A metallo‐supramolecular block copolymers.

Telechelic polymers bearing a terpyridine end‐group at the α‐position and a nitroxide at the ω‐position were prepared in a living fashion by nitroxide‐mediated polymerization.     

A Novel Crystallization Scheme in Poly[styrene‐block‐(ferrocenyl dimethylsilane)] Diblock Copolymers

Isothermal crystallization of the poly(ferrocenyl dimethylsilane) (PFDMS) segments in a poly[styrene‐block‐(ferrocenyl dimethylsilane)] (PS‐b‐PFDMS) diblock copolymer of lamellar micro‐morphology has been investigated. The PFDMS is shown to crystallize in a confined and grain‐by‐grain fashion. Here a ‘grain’ is defined as an ensemble of stacked lamellae wherein the PFDMS crystallization spreads quickly but stops at its surroundings. Such crystallization propagates not only along the PFDMS lamellae but across the amorphous PS layers as well. We suggest that conformational changes in the PS as induced by the PFDMS crystallization (‘squeezing transfer’) are responsible for the latter pathway of the crystallization's spread.

     

Nanostructure Evolution of Homogeneous Poly(ethylene‐co‐1‐octene) as a Function of Strain

Polyolefin elastomers with varying 1‐octene content and different thermal history are studied by wide‐angle X‐ray scattering (WAXS) and small‐angle X‐ray scattering (SAXS) during drawing and after relaxation. The multidimensional chord distribution function (CDF) reveals the nanostructure made from crystallites in the amorphous matrix. Both lamellae and granular crystals are found. Lamellae do not form stacks. The SAXS peak is observed because each lamella is covered by an amorphous layer of well‐defined thickness. Arrangement, rotation, fine chain slip and failure of the domains are directly observed as a function of elongation. During straining and relaxation a well oriented macrolattice with colloidal dimensions but short‐ranging order is formed. Two processes are generating microfibrils, namely (1) arrangement of granular crystallites, and (2) irreversible disruption of lamellae (coarse slip) followed by arrangement of their fragments. The second process stabilizes the colloidal lattice permanently. The higher the comonomer content, the later the irreversible process starts. Quenching from the melt shifts the onset to lower deformation. Deformation of microfibrils is not homogeneous. Instead, there is a limiting long period that cannot be exceeded without disruption. It is related to the position of the maximum in the SAXS pattern (which is almost constant).

Long periods in the CDF z(r₁₂, r₃) of an ethylene‐octene block copolymer after relaxation from drawing.     

Aniline‐Based Disulfide/Aniline Copolymers as a High Energy‐Storage Material

Aniline‐based disulfide, 5‐amino‐1,4‐dihydrobenzo[d]‐1′,2′‐dithiadiene (DTAn), was synthesized through a new route. The DTAn/aniline copolymers [P(DTAn‐co‐An)] were prepared by chemical oxidative polymerization. The results show that the polymerization activity of the DTAn is obviously lower than that of aniline, and the degree of polymerization increases with the increasing feed ratio of aniline and oxidant dosage. The cyclic voltammograms of the copolymers indicate that intramolecular self‐catalyzed effects occurred between the conducting backbone and the S‐S side chain. The charge–discharge tests of Li/P(DTAn‐co‐An) cell show an initial specific capacity of 262 mAh · g⁻¹, which suggests that P(DTAn‐co‐An) may be a promising cathode material in secondary lithium batteries.

     

Light‐Tunable Thermosensitivity of Polymer‐Coated Gold Nanoparticles Achieved by Light‐Controlled Molecular Recognition

Thermo‐ and photosensitive gold nanoparticles (AuNPs) coated with an azobenzene‐contained P(DMA‐PAPA‐MAEL) copolymer are prepared by ligand exchange reactions. The photoisomerization of azobenzene moiety on the surface of P(DMA‐PAPA‐MAEL)‐coated AuNPs is detected by means of UV‐Vis spectroscopy with the presence or absence of free α‐cyclodextrin. When subjected to visible and UV light irradiation alternately, P(DMA‐PAPA‐MAEL)‐coated AuNPs in the presence of free α‐CD display a light‐tunable lower critical solution temperature through light‐controlled molecular recognition between the azobenzene moiety on the surface of AuNPs and free α‐CD.

     

pH‐Sensitive Micelles Formed by Interchain Hydrogen Bonding of Poly(methacrylic acid)‐block‐Poly(ethylene oxide) Copolymers

pH‐sensitive micelles formed by interchain hydrogen bonding of poly(methacrylic acid)‐block‐poly(ethylene oxide) copolymers were prepared and investigated at pH < 5. Both and R_h of the micelles increase with decreasing pH of the solution, displaying an asymptotic tendency at low pH values. The observed micelles are well‐defined nanoparticles with narrow size distributions (polydispersity ΔR_h/R_h ≤ 0.05) comparable with regular diblock copolymer micelles. The CMCs occur slightly below c = 1 × 10^?4 g · mL^?1. The micelles are negatively charged and their time stability is lower than that of regular copolymer micelles based purely on hydrophobic interactions.

     

Synthesis and Micellization of Star‐Shaped Poly(ethylene glycol)‐block‐Poly(ε‐caprolactone)

Summary: The relationship between the architecture of block copolymers and their micellar properties was investigated. Diblock, 3‐arm star‐shaped and 4‐arm star‐shaped block copolymers based on poly(ethylene glycol) and poly(ε‐caprolactone) were synthesized. Micelles of star‐shaped block copolymer in an aqueous solution were then prepared by a solvent evaporation method. The critical micelle concentration and the size of the micelles were measured by the steady‐state pyrene fluorescence method and dynamic light scattering, respectively. The CMC decreased in the order di‐, 3‐arm star‐shaped and 4‐arm star‐shaped block copolymer. The size of the micelles increased in the same order as the CMC. Theory also predicts that the formation of micelles becomes easier for 4‐arm star‐shaped block copolymers than for di‐ and 3‐arm star‐shaped block copolymers, which qualitatively agrees with the experiments.