Crystallization of the polyethylene block in polystyrene‐b‐polyethylene‐b‐polycaprolactone triblock copolymers, 1. Self‐nucleation behavior

The self‐nucleation of branched polyethylene chains of different degrees of chain mobility was studied. The polyethylene block (PE block) within poly(styrene‐b‐ethylene‐b‐caprolactone) triblock copolymers (SEC) of varying compositions was studied. Differential scanning calorimetry was used to determine the self‐nucleation domains as a function of the self‐nucleation temperature (T_s). The self‐nucleation behavior of PE chains within SEC block copolymers was found to be anomalous in comparison to the classical self‐nucleation behavior exhibited by homopolymers. When the degree of chain constraint is high, as in the case where the SEC copolymer only contains 15% of PE, domain II (only self‐nucleation domain) completely disappears and annealing can take place before self‐nucleation occurs. This means that chain constraint complicates the self‐nucleation process and this situation persists until, upon decreasing the self‐nucleation temperature (T_s), annealing has generated crystals that are big enough to act as self‐nuclei for the less restricted portions of the chain. If the PE content in the copolymer is very low (15%), two crystal populations can be distinguished. This may reflect the differences in diffusion of the PE chain segments close to the interfaces with the other two blocks and those segments that are close to the middle of the PE block. The influence of chain constraint on determining the difficulty of the chains to self‐nucleate was further explored using a crosslinked low‐density polyethylene (XLDPE). In this case, crosslinking junctions instead of covalent links with other blocks restrict chain mobility. Nevertheless, a similar difficulty in self‐nucleation was found as in the case of the PE block within SEC triblock copolymers in contrast to neat LDPE, a polymer that exhibited the classical self‐nucleation behavior with the usual three domains.     

Synthesis and Characterization of Epoxidized Styrene‐Butadiene Block Copolymers as Templates for Nanostructured Thermosets

Summary: A wide range of epoxidized styrene‐block‐butadiene block copolymers were synthesized using hydrogen peroxide in the presence of an in situ prepared methyltrioctylammoniumtetrakis(diperoxotungstate)phosphate as the catalyst system in a water/dichloroethane biphasic system. ¹H NMR and FT‐IR spectra revealed that the epoxidation procedure led mainly to 1,4‐epoxidized butadiene units. GPC analysis showed that epoxidation changed the copolymer architecture into stars with fewer arms. The copolymers showed two glass transition temperatures in accordance with the phase separation for block copolymers and, as revealed in AFM images, the self‐assembly takes place on a nanometer scale. Moreover, epoxidized styrene‐butadiene (SB) copolymers showed improved miscibility with epoxy monomers leading to self‐assembled nanostructures in the uncured state. This allows them to be used as templates for nanostructured resins.

TM‐AFM phase images for: a) 40 mol‐% epoxidized copolymer (scale bar = 300 nm); b) uncured blend containing 50 wt.‐% DGEBA in 50 mol‐% epoxidized copolymer (scale bar = 1 μm), after annealing at 80 °C in vacuum for 3 h.     

Double Hydrophilic Block Copolymer Self‐Assembly in Aqueous Solution

Self‐assembly of double hydrophilic block copolymers (DHBCs) in water is an emerging area of research. The self‐assembly process can be derived from aqueous two‐phase systems that are composed of hydrophilic homopolymers at elevated concentration. Consecutively, DHBCs form self‐assembled structures like micelles, vesicles, or particles at high concentrations in water and without the use of external triggers that would change solubility of individual blocks. Careful choice of the two hydrophilic blocks and design of the polymer structure allows formation of self‐assembled structures with high efficiency. The present contribution highlights recent research in the area of DHBC self‐assembly, including the polymer types employed and strategies for crosslinking of the self‐assembled structures. Moreover, an overview of aqueous multiphase systems and theoretical considerations of DHBC self‐assembly are presented, as well as an outlook regarding potential future applications in areas such as the biomedical field.     

pH‐Responsive Double‐Hydrophilic Block Copolymers: Synthesis and Drug Delivery Application

A novel double‐hydrophilic block copolymer P(MEO₂MA‐co‐OEGMA)‐b‐PAMA has been successfully synthesized by two‐step RAFT polymerization. Then, the amino groups of PAMA blocks in the copolymers react with 1‐pyrenecarboxaldehyde via a “Schiff‐base” reaction, and the resulting copolymers are self‐assembled to form spherical micelles in aqueous solution. Because the “Schiff‐base” linkage is pH sensitive, the release rate of pyrene depends upon the pH of solution. Complete release is achieved at pH 1, and the control release is much faster at pH 5.5 than that at pH 7.4. With progress of pyrene release, the micelles are disassembled gradually and disappeared completely at last. This double‐hydrophilic copolymer is a promising candidate of drug carrier for the aldehyde‐ containing hydrophobic drugs.     

Aggregation and Crosslinking of Poly(N,N‐dimethylacrylamide)‐b‐pullulan Double Hydrophilic Block Copolymers

The self‐assembly of polymers is a major topic in current polymer chemistry. In here, the self‐assembly of a pullulan based double hydrophilic block copolymer, namely pullulan‐b‐poly(N,N‐dimethylacrylamide)‐co‐poly(diacetone acrylamide) (Pull‐b‐(PDMA‐co‐PDAAM)) is described. The hydrophilic block copolymer induces phase separation at high concentration in aqueous solution. Additionally, the block copolymer displays aggregates at lower concentration, which show a size dependence on concentration. In order to stabilize the aggregates, crosslinking via oxime formation is described, which enables preservation of aggregates at high dilution, in dialysis and in organic solvents. With adequate stability by crosslinking, double hydrophilic block copolymer (DHBC) aggregates open pathways for potential biomedical applications in the future.     

Universal Bioinert Control of Polystyrene Interfaces via Hydrophobic‐Driven Self‐Assembled Surface PEGylation with a Well‐Defined Block Sequence

This work proposes a new molecular insight of interfacial design in the control of antifouling performance for the versatile biofoulants, including proteins, blood cells, tissue cells, and bacteria. A self‐assembled bioinert interface with universal fouling resistance to general biofoulants via hydrophobic‐driven surface PEGylation is presented. The study systematically discriminates the optimum PEGylated block polymer configuration and hydrophobic/hydrophilic segmental ratio enabling to optimize the surface coverage by the bioinert moieties, thus ensuring the best resistance to biofouling. For similar copolymer molecular weights and similar polystyrene (PS)/poly(ethylene glycol) methacrylate (PEGMA), the coating density obtainable is the highest if a random copolymer is used, while it is the lowest with a triblock copolymer. That measured with a diblock copolymer lies in between. Random copolymers offer more numerous anchoring possibilities than diblock copolymers, while they are importantly fewer if triblock copolymers are used. For similar total number of hydrophilic blocks, the diblock copolymer is more efficient to resist larger cells (leukocytes, fibroblasts) while the triblock is better to promote mitigate biofouling by smaller molecules or cells (proteins, platelets, red blood cells). The length of the hydrophilic PEGylated block seems to dominate fouling resistance of large biofoulants.     

One‐Step Spontaneous Formation of Dual Wrinkling on Uniform‐Sized Microparticles Induced by Surface

This study demonstrates the wrinkle formation on biodegradable polymer‐blend microparticles prepared from an emulsion‐solvent evaporation method and investigates the formed patterns. A labyrinthine pattern is obtained for uniform‐sized microparticles, owing to the considerable size reduction during solvent evaporation. Changing the radius of the organic droplets dispersed in the aqueous solution switches the wrinkle pattern from labyrinth to bi‐phase. For the first time, the dual wrinkling structure is prepared; both labyrinthine texture and hexagonal dimple structures are spontaneously formed on the same microparticle surface. The former pattern is due to the surface instability from blends of hydrophobic polymer and amphiphilic block copolymer, while the latter is due to a mechanism similar that of the breath figure formed with organic phase change materials during solidification of microparticles. The general applicability of this approach is demonstrated on other pairs of polymer blends.     

Poly(2‐vinylnaphthalene)‐block‐poly(acrylic acid) Block Copolymer: Self‐Assembled Pattern Formation,Alignment, and Transfer into Silicon via Plasma Etching

P2VN‐b‐PAA is a novel diblock copolymer which has potential as a self‐assembled nanoscale patterning material. Thin spin cast P2VN‐b‐PAA films rapidly reorganize to vertical lamellar with exposure to acetone vapor. P2VN‐b‐PAA lamellar morphology was aligned by electric field under acetone vapor at a significantly faster rate and at lower electric field strengths than other polymer systems. Observed dry etching selectivity for P2VN to PAA were comparatively high for a variety of etch gases, consistent with estimations from Ohnishi and ring parameters. Block copolymer self assembled patterns were transferred to silicon via two‐step CF₄ and SF₆ etching.

     

Complexation of Amino‐Acid‐Based Block Copolymers With Dual Thermoresponsive Properties and Water‐Soluble Silsesquioxane Nanoparticles

Smart organic–inorganic hybrids are prepared using non‐covalent interactions between water‐soluble silsesquioxane nanoparticles and two amino acid‐based block copolymers prepared by reversible addition–fragmentation chain transfer (RAFT) polymerization. A block copolymer displaying lower critical solution temperature (LCST) and upper critical solution temperature (UCST) is employed, in which only poly(N‐acryloyl‐4‐trans‐hydroxy‐L ‐proline) segment could interact with the nanoparticles, whereas another poly(N‐acryloyl‐L ‐proline methyl ester) segment shows a thermoresponsive property without any interaction. The complexation of another type of dual thermosensitive block copolymer with two different LCSTs and the silsesquioxane nanoparticles is also investigated.     

Poly(4‐vinyl imidazole): A pH‐Responsive Trigger for Hierarchical Self‐Assembly of Multicompartment Micelles Based upon Triblock Terpolymers

Poly(vinyl pyridine) has widely been used as a pH‐responsive polymer to trigger changes in self‐assembly of block copolymer micelles. However, the polymer is known to display toxic features, which limits its ultimate applicability for biological applications. Here, poly(4‐vinyl imidazole) (P4VIm), a much more biocompatible polymer, is used as a pH‐responsive block to modulate the self‐assembly of ABC triblock terpolymers. In this article, the synthesis of the poly(1‐acryloyl fructopyranose)‐block‐ poly(n‐butyl acrylate)‐block‐ poly(4‐vinyl imidazole) (PFruA₅₂‐b‐PBuA₃₀₀‐b‐P4VIm₂₅₀) triblock terpolymers is first discussed by sequential reversible addition fragmentation chain transfer (RAFT) polymerization. Subsequently, the structure formation of the triblock terpolymer is elucidated by step‐wise solvent exchange. The polymer readily dissolves in methanol, but self‐assembles into micelles with PBuA cores and mixed shell in methanol–water mixtures. Solvent exchange against buffer solutions of pH 6–6.5 leads to collapse of P4VIm due to deprotonation and induces self‐assembly into caterpillar‐like non‐spherical nanoparticles, most likely via the formation of intermediate Janus particles. The rearrangement into larger hierarchical structure, as seen by small angle X‐ray scattering (SAXS), is found to process within several hours. The article is concluded by demonstrating lower cytotoxicity values for the present polymer in comparison to a structurally analogous triblock terpolymer based on poly(vinyl pyridine).     

Size Tunable Core Crosslinked Micelles from HPMA‐Based Amphiphilic Block Copolymers

A variety of core crosslinkable hydroxypropylmethacrylamide‐based block copolymers are synthesized by reversible addition‐fragmentation chain transfer (RAFT) polymerization, which are composed of hydroxypropyl‐methacrylate as hydrophilic block combined with a statistical hydrophobic block from laurylmethacrylate and the photo crosslinkable monomer. It is discovered that the self‐assembled micellar aggregates from these systems vary strongly in size depending not only on the velocity of the polarity switch (nanoprecipitation or slow dialysis) but also on the solvent from which they were dialyzed. In this way micellar aggregates with an R _h varying between 15 and 80 nm can be prepared from the same block copolymer. In addition, a new hydrophobic crosslinkable hymecromone moiety is introduced. In this way the differently sized nanoparticles can be effectively stabilized by photo‐crosslinking, leading to a high stability of the photo crosslinkable polymeric micelles against disintegration by detergents.     

Block Copolymer Micelle Nanotubes by the Solvent‐Annealing‐Induced Nanowetting in Anodic Aluminum Oxide Templates

Block copolymer micelles are generally formed by the self‐assembly of amphiphilic copolymer molecules in aqueous medium. Although different types of block copolymer micelles have been studied, the self‐assembly behavior of block copolymer micelles in confined geometries have been rarely studied. In this work, the fabrication of polystyrene‐block‐poly(4‐vinylpyridine) (PS‐b‐P4VP) micelle nanotubes in the cylindrical nanopores of anodic aluminum oxide templates using a solvent‐annealing‐assisted wetting method is presented. The PS‐b‐P4VP chains wet the pore walls in the form of micelles when the sample is annealed in the vapor of toluene, a good solvent for PS and a nonsolvent for P4VP. The formation of the PS‐b‐P4VP micelle nanotubes instead of nanorods implies that the micelles wet the nanopores in the complete wetting regime. This study not only contributes to a deeper understanding of the self‐assembly behavior of block polymer micelles in confined geometries, but also provides more possible variations and design freedoms in the application of block copolymer micelles.

     

Mesh‐Like Vesicles Formed From Blends of Poly(4‐vinyl pyridine)‐b‐polystyrene‐b‐poly(4‐vinyl pyridine) Block Copolymers via Gradual Blending Method

In this study, we developed a novel blending strategy, namely, the gradual blending method, to tune the micellar structure. Different from the most commonly used premixing blending method, which different block copolymers are premixed in a common solvent before their individual self‐assembly, the gradual blending method involves gradually adding one type of block copolymer into the pre‐generated micellar solution formed from another type of block copolymer. Moreover, we obtained a novel mesh‐like vesicle from the self‐assembly of the mixtures of P4VP₄₃‐b‐PS₂₆₀‐b‐P4VP₄₃ and P4VP₄₃‐b‐PS₃₆₆‐b‐P4VP₄₃ in 1,4‐dioxane/water solution using the gradual blending method.     

Effects of Poly(N‐isopropylacrylamide) (PNIPAAm) on the Conformational Change of Poly(N 5‐hydroxyalkyl glutamine) (PHAG) in PHAG‐PNIPAAm Block Copolymer with Temperature

Diblock copolymers consisting of poly(N ⁵‐hydroxyalkylglutamine) (PHAG) and poly(N‐isopropylacrylamide) (PNIPAAm) were prepared by aminolysis with aminoalkanols of the side‐chain ester of poly(γ‐benzyl L ‐glutamate) (PBLG) as a part of PBLG‐PNIPAAm block copolymers. The molecular weight ratio of the initial PBLG to the resulting PHAG was nearly 0.35. The effect of PNIPAAm on the conformational change of PHAG in PHAG‐PNIPAAm block copolymers with temperature was investigated by circular dichroism. Poly[N ⁵‐(2‐hydroxyethyl)‐L ‐glutamine] (PHEG) and the PHEG‐PNIPAAm copolymer (GNE) stayed in a randomly coiled conformation whereas poly[N ⁵‐(3‐hydroxypropyl)‐L ‐glutamine] (PHPG), poly(N ⁵‐(4‐hydroxybutyl)‐L ‐glutamine) (PHBG), PHPG‐PNIPAAm copolymer (GNP), and PHBG‐PNIPAAm copolymer (GNB) underwent conformational transitions with temperature. The conformational change of the PHPG block in GNP copolymer occurred from an α‐helix to a random coil after the incorporation of PNIPAAm into the copolymer. The thermodynamic parameters of the thermally induced helix‐coil transition for PHBG and PHBG‐PNIPAAm in aqueous solution were calculated.     

Novel Olefin Block Copolymer,Polypropene‐block‐poly(methylene‐1,3‐cyclopentane‐co‐propene), Synthesized from Propene and 1,5‐Hexadiene by a Modified Stopped‐Flow Method

A block copolymer of propene and 1,5‐hexadiene, polypropene‐block‐poly(methylene‐1,3‐cyclopentane‐co‐propene) (PP‐b‐(PMCP‐co‐PP)), was synthesized using a modified stopped‐flow polymerization method with an MgCl₂‐supported Ziegler catalyst. Regarding the basic characteristics of the PP‐b‐(PMCP‐co‐PP), the block formation was investigated in detail. The obtained block copolymer showed a unimodal GPC curve without any peak in the low molecular weight region. It was also clear that the molecular weight of each part could be controlled by changing the polymerization time (from about 0.1 to 0.2 s). Furthermore, the elution pattern by temperature‐rising elution fractionation clearly showed that the block copolymer eluted in each temperature region between 20°C to 120°C was mainly composed of a unified component. Even after extraction with boiling heptane, the ¹³C NMR spectra of the block copolymer showed that the signals from PMCP‐co‐PP remained unchanged, but disappeared in the blend of polypropene and PMCP‐co‐PP. The differential scanning calorimetry results and optical microscopic observations indicated not only the formation of a block copolymer having a chemical linkage between polypropene and PMCP‐co‐PP, but also the regulation of the crystalline distribution in the block copolymer by changing the composition of each block part.     

RAFT Synthesis and Solution Properties of pH‐Responsive Styrenic‐Based AB Diblock Copolymers of 4‐Vinylbenzyltrimethylphosphonium Chloride with N,N‐Dimethylbenzylvinylamine

The RAFT synthesis and solution properties of AB block copolymers of 4‐vinylbenzyltrimethylphosphonium chloride (TMP) and N,N‐dimethylbenzylvinylamine (DMBVA) is described. The pH‐dependent self‐assembly properties of the AB diblock copolymers were examined using of ¹H NMR, DLS, and fluorescence spectroscopy. The size of the polymeric aggregates depends on the block copolymer composition/molecular mass. The self assembly is completely reversible, as predicted from the tunable hydrophilicity/hydrophobicity of the DMBVA residues. The AB diblock copolymers can be effectively locked in the self‐assembled state using a straightforward core crosslinking reaction between the tertiary amine residues of DMBVA and difunctional 1,4‐bis(bromomethyl)benzene.

     

Controlled ROMP Synthesis of Ferrocene‐Containing Amphiphilic Dendronized Diblock Copolymers as Redox‐Controlled Polymer Carriers

Novel well‐defined redox‐responsive Ferrocene (Fc)‐containing amphiphilic dendronized diblock copolymers are synthesized by the ring‐opening metathesis polymerization technique using Grubbs’ third‐generation olefin metathesis catalyst as the initiator. These dendronized block copolymers can self‐assemble into spherical micelles in aqueous solution. The size of self‐assembled micelles can be modulated by the composition (namely, the ratio of hydrophobic and hydrophilic segments) and concentration of the dendronized copolymers. The obtained micelles show reversible redox‐controlled self‐assembly behaviors using FeCl₃ as oxidant and glutathione as reductant. Furthermore, the model molecule Rhodamine B is successfully loaded in these micelles, and the oxidation‐triggered controllable release is achieved by changing the type of oxidants (FeCl₃ and H₂O₂) and their concentrations. This is the first example of redox‐responsive micelles self‐assembled by novel amphiphilic dendronized Fc‐containing block copolymers, and the present micelles are visualized to be potential candidates in many fields, especially in stimuli‐responsive drug delivery systems.     

Directing the Smectic Layer Orientation by Shear Flow in Hierarchical Lamellar‐within‐lamellar Liquid Crystalline Diblock Copolymers

A self‐assembled lamellar‐within‐lamellar structure of a side chain liquid crystalline diblock copolymer was shear aligned to induce overall alignment and to direct the smectic layer orientation within the copolymer lamellae. The copolymer consisted of a polystyrene block and a poly(methyl methacrylate) block bearing cholesteryl mesogens with only short oxycarbonyloxyethyl spacers separating the mesogens from the backbone. Upon shearing, the copolymer lamellae exhibited uniaxial alignment whereas the smectic layers of the mesogens showed coexisting perpendicular and parallel orientations with respect to the copolymer lamellae. The fraction of the parallel oriented domains could be systematically increased by tuning the oscillation frequency and strain amplitude.

     

Double‐Gyroid Morphology of a Polystyrene‐block‐Poly(ferrocenylethylmethylsilane) Diblock Copolymer: A Route to Ordered Bicontinuous Nanoscale Architectures

A polystyrene‐block‐poly(ferrocenylethylmethylsilane) diblock copolymer, displaying a double‐gyroid morphology when self‐assembled in the solid state, has been prepared with a PFEMS volume fraction ?_PFEMS = 0.39 and a total molecular weight of 64 000 Da by sequential living anionic polymerisation. A block copolymer with a metal‐containing block with iron and silicon in the main chain was selected due to its plasma etch resistance compared to the organic block. Self‐assembly of the diblock copolymer in the bulk showed a stable, double‐gyroid morphology as characterised by TEM. SAXS confirmed that the structure belonged to the Ia d space group.

     

Tetraphenylsilane‐Cored Star‐Shaped Amphiphilic Block Copolymers for pH‐Responsive Anticancer Drug Delivery

Four‐arm star‐shaped poly[2‐(diethylamino)ethyl methacrylate]‐b‐poly[2‐hydroxyethyl methacrylate]s block copolymers using tetraphenylsilane (TPS) as a core with adjustable arm lengths are synthesized through two‐step atom transfer radical polymerizations. For comparison, a linear block copolymer with similar molecular weight is also prepared. The assembled star‐shaped copolymer micelles exhibit sizes of 102–139 nm and critical micelle concentrations of 1.49–3.93 mg L^?1. Moreover, the bulky and rigid TPS core is advantageous for propping up the four star‐shaped arms to generate large intersegmental space. As a result, the drug‐loading capacity in the micelles is up to 33.97 wt%, much surpassing the linear counterpart (8.92 wt%) and the previously reported star‐shaped copolymers prepared using pentaerythritol as the core. Furthermore, the micelles show sensitive pH‐responsive drug release when the pH changes from 7.4 to 5.0. The in vitro cytotoxicity to Hela cells indicates that the doxorubicin (DOX)‐loaded micelles have similar anticancer activity to the pristine DOX. The combination of excellent micelle stability, high drug‐loading, sensitive pH response, and good anticancer activity endows the copolymers with promising application in drug control delivery for anticancer therapy.