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.

     

Thermo‐Responsive Hydrogels with Nanodomains: Rapid Shrinking of a Nanogel‐Crosslinking Hydrogel of Poly(N‐isopropyl acrylamide)

Rapidly shrinking poly(N‐isopropyl acrylamide) (PNIPAM) hydrogels are prepared by crosslinking with self‐assembled nanogels that consist of cholesteryl‐ and methacryloyl‐substituted pullulan (CHPMA). The CHPMA nanogel (R_h = 26.4 nm) was used as a crosslinker for a hydrophilic nanodomain. Transmission electron microscopy images of the nanogel‐crosslinked PNIPAM hydrogel reveal a well‐defined nanoporous structure. The nanogel‐crosslinked PNIPAM hydrogel shows rapid shrinking based on its structure. The shrinking half‐time was ≈2 min, which is about 3 400 times faster than that of a PNIPAM hydrogel crosslinked by methylene(bisacrylamide).

     

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.

     

Raspberry‐Like Aggregates Containing Secondary Nanospheres of Polystyrene‐block‐poly(4‐vinylpyridine) Micelles

Summary: Raspberry‐like aggregates containing secondary nanospheres were studied. The formation of raspberry‐like aggregates was due to complexation between core‐shell microspheres and core‐corona micelles. The core‐shell microspheres were synthesized with soap‐free polymerization of styrene and methyl acrylic acid, which included carboxyl groups in the periphery. The micelles were self‐assembled by polystyrene‐block‐poly(4‐vinylpyridine), which contained pyridine groups in the corona. The driven force to form raspberry‐like aggregates was due to the affinity between the carboxyl and pyridine groups. The morphology of the raspberry‐like aggregates could be tuned by changing the ratio of the microspheres to micelles. IR measurements suggested that the raspberry‐like aggregates were like zwitterions.

TEM image of the raspberry‐like aggregates formed at a molar ratio of MAA to 4VP at 1:4.     

Synthesis and Self‐Assembly of pH‐Responsive Amphiphilic Poly(dimethylaminoethyl methacrylate)‐block‐Poly(pentafluorostyrene) Block Copolymer in Aqueous Solution

We report the synthesis of a novel pH‐responsive amphiphilic block copolymer poly(dimethylaminoethyl methacrylate)‐block‐poly(pentafluorostyrene) (PDMAEMA‐b‐PPFS) using RAFT‐mediated living radical polymerization. Copolymer micelle formation, in aqueous solution, was investigated using fluorescence spectroscopy, static and dynamic light scattering (SLS and DLS), and transmission electron microscopy (TEM). DLS and SLS measurements revealed that the diblock copolymers form spherical micelles with large aggregation numbers, N_agg ≈ 30 where the dense PPFS core is surrounded by dangling PDMAEMA chains as the micelle corona. The hydrodynamic radii, R_h of these micelles is large, at pH 2–5 as the protonated PDMAEMA segments swell the micelle corona. Above pH 5, the PDMAEMA segments are gradually deprotonated, resulting in a lower osmotic pressure and enhanced hydrophobicity within the micelle, thus decreasing the R_h. However, the radius of gyration, R_g remains independent of pH as the dense PPFS cores predominate.

     

Fabrication of Compositional‐Gradient Biodegradable Polymeric Films Showing Self‐Bending Deformation

A compositional graded film of poly(ε‐caprolactone) (PCL) with 4,4′‐thiodiphenol (TDP), in the film thickness direction, was fabricated by self‐diffusing of TDP in the PCL melt. We found out the self‐bending deformation of the gradient film, which bent into a rolled‐up shape by itself. The initial shape of the film was flat when the sample was quenched from the melt. Upon the fast crystallization of PCL, the gradient film bent to the side with low TDP content. Then, after PCL crystallized the film bent to the opposite direction, that is, to the side with high TDP content. This bending to the TDP rich region was induced by not only the crystallization of PCL but also mass transfer due to the diffusion of TDP from TDP rich region to poor region.

     

Ordered Honeycomb‐Structured Films from Dendronized PMA‐b‐PEO Rod‐Coil Block Copolymers

Summary: Fabrication of honeycomb‐patterned films from amphiphilic dendronized block copolymer (PEO₁₁₃‐b‐PDMA₈₂) by ‘on‐solid surface spreading’ and ‘on‐water spreading’ method is reported. Highly ordered honeycomb films with quasi‐horizontally paralleled double‐layered structure can be fabricated by the on‐solid surface spreading method. This work raises the possibility that such structures can be formed in amphiphilic dendronized block copolymers and extends the family of source materials.

     

Phase Transition Behaviors of Self‐Oscillating Polymer and Nano‐Gel Particles

Summary: Self‐oscillating polymers and nano‐gel particles consisting of N‐isopropylacrylamide and the ruthenium catalyst of the Belousov‐Zhabotinsky reaction have been prepared. In order to clarify the crosslinking effect on the self‐oscillating behavior, the phase transition behaviors were investigated by measuring the transmittance and the fluorescence intensity of the polymer solution and the gel bead suspension. Cooperative effects due to crosslinking will play an important role for the design of nanoactuators.

Chemical structure of poly(NIPAAm‐co‐Ru(bpy)₃).     

A New Type of Thermoresponsive Copolymer with UCST‐Type Transitions in Water: Poly(N‐vinylimidazole‐co‐1‐vinyl‐2‐(hydroxymethyl)imidazole)

1‐Vinyl‐2‐(hydroxymethyl)imidazole ( 2 ) is synthesized by a procedure described in the literature. Corresponding copolymers with upper critical solution temperature (UCST)‐type transitions in water and high‐glass transition temperatures (T_g) are prepared by free radical copolymerization with N‐vinylimidazole ( 1 ). Depending on the copolymer composition, the cloud point can be varied between 19 and 41 °C. As the copolymer composition is identical with the monomer feed ratio, the cloud point can be easily tuned in the desired range. Furthermore, a distinctive pH‐dependence and salt effect can be observed.

     

Nanosized Shape‐Changing Colloids from Liquid Crystalline Elastomers

A method to prepare shape‐changing nanospheres from liquid crystalline elastomers is reported. The nanosized colloids are prepared by a miniemulsion process. During this process, colloids are prepared from a liquid crystalline (LC) main‐chain polyester and subsequently crosslinked into a nanometer‐sized LC elastomer. The ability of these LC elastomers to change their shape at the phase transition temperature from the smectic A to the isotropic phase was detected by temperature‐dependent transmission electron microscopy. The phase transition‐induced shape change leads to strongly shape anisotropic nanosized elastomer particles.

     

Shell Cross‐Linked Micelles as Cationic Templates for the Preparation of Silica‐Coated Nanoparticles: Strategies for Controlling the Mean Particle Diameter

The mean diameter of poly[2‐(dimethylamino)ethyl methacrylate]‐block‐poly[2‐(diisopropylamino)ethyl methacrylate] (PDMA‐PDPA) diblock copolymer micelles can be easily adjusted from 27–155 nm (as measured by DLS) by either selective quaternisation of the PDMA block or by adding PDPA homopolymer prior to micellisation; these self‐assembled nanostructures can be shell crosslinked with 1,2‐bis‐(2‐iodoethoxy)ethane and subsequently used as templates for the preparation of silica‐coated nanoparticles and, ultimately, hollow silica nanoparticles.

     

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.

     

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.     

Preparation of Polar Ethylene–Norbornene Copolymers by Metallocene Terpolymerization with Triisobutylaluminium‐Protected But‐3‐en‐1‐ol

But‐3‐en‐1‐ol has been pre‐protected by triisobutylaluminium and terpolymerized with ethylene and norbornene by rac‐[Et(Ind)₂]ZrCl₂/MAO catalysts. The strong polarity of diisobutyl(but‐3‐en‐1‐oxy)aluminum causes a slight reduction in the catalyst activity and yields a small fraction of crystallinity. The but‐3‐en‐1‐ol content in the terpolymer is as high as 3.2% and can be readily adjusted by varying the reaction conditions. When the norbornene/ethylene ratio is over 10, the norbornene incorporation efficiency is not affected by the polar monomer and is close to that of the copolymerization. Similar to the ethylene/norbornene copolymers, the thermal properties of the obtained terpolymers are mainly determined by their norbornene contents.

     

Square Lamellar Structure Having Phase‐Separated Microdomain in H‐Shaped Block Copolymer Thin Film

The morphology of a H‐shaped block copolymer (poly(ethylene glycol) backbone and polystyrene branches (PS)₂PEG(PS)₂) in a thin film has been investigated. A peculiar square lamella that has a phase‐separated microdomain at its surface is obtained after spin coating. The experimental temperature plays a critical role in the lamellar formation. The copolymer first self‐assembles into square lamellar micelles with an incomplete crystalline core due to the crystallizability of PEG. In the subsequent process of solvent evaporation, phase separation between PS and non‐crystalline PEG attached at the chain‐folded PEG surface takes place, which results in phase‐separated microdomains being formed at the lamellar surface.

     

Polypeptoids by Living Ring‐Opening Polymerization of N‐Substituted N‐Carboxyanhydrides from Solid Supports

The nucleophilic living ring‐opening polymerization of N‐substituted glycine N‐carboxyanhydrides using solid‐phase synthesis resins is reported. By variation of experimental parameters, products with near Poisson distributions are obtained. As opposed to reversible deactivation radical polymerization, the living polymerization is demonstrated to be viable to high monomer conversion and through multiple monomer addition steps. Successful preparation of a multiblock copolypeptoid is proof for a highly living and robust character of the solid‐phase peptoid polymerization.

     

Dual Stimuli‐Responsive Polymeric Micelles Exhibiting “AND” Logic Gate for Controlled Release of Adriamycin

A new controlled release polymer micelle was designed and synthesized based on the concept of the “AND” logic with two orthogonal molecular triggers, namely pH and reduction, for intracellular drug delivery. Specifically, a hydrazine functionalized PEO‐b‐PMAA block copolymer was used to attach adriamycin (ADR) through the formation of hydrazone, then the as‐prepared ADR‐conjugated block copolymer micelles could be crosslinked by dithiodiethanoic acid. ADR was found to release most efficiently under both the low pH and the reductive conditions. This smart device is therefore equipped with two triggers with the “AND” logic for the releasing action, which is suitable for more complicated physiological conditions because the “ON” state is only realized under the simultaneous presence of the dual signal stimuli.

     

Construction of Large‐Scale Highly Ordered Macroporous Monoliths of π‐Conjugated Polymers

Large scale of well‐ordered macroporous π‐conjugated polymer monoliths have been successfully prepared through a new approach using micrometer‐sized naphthalene crystals as templates. The macroporous monoliths of poly(p‐phenylenevinylene) (PPV) and poly(p‐phenyleneethynylene) (PPE) grew along the unidirectional freezing direction inside the template naphthalene crystals which lead to the formation of controlling morphologies and homogeneous diameters. The polymer monoliths show straight and lamella macroporous structures. The diameters of pores and the thickness of pore walls can be controlled by tuning the freezing temperature.

     

Regulation of Micellar Morphology of PCL‐b‐PEO Block Copolymers by Crystallization Temperature

The effect of crystallization temperature on the micellar morphology of PCL‐b‐PEO block copolymers in water has been studied. It is found that the micellar morphology of PCL_nPEO₄₄ and PCL_nPEO₁₁₃ changes with crystallization temperature in different ways because of two competitive factors: perfection of the PCL crystals in the core and deformation of the soluble PEO block. For PCL_nPEO₄₄, perfection of the PCL crystals dominates the micellar morphology and lamellar micelles are formed at a higher crystallization temperature. For PCL_nPEO₁₁₃ the micellar morphology is mainly determined by the tethering density and spherical micelles or cylindrical micelles with a larger length/diameter ratio are formed at a higher crystallization temperature because of the larger tethering density.

     

Multiple Morphologies and Their Transformation of a Polystyrene‐block‐poly(4‐vinylpyridine) Block Copolymer

Summary: We report the multiple morphologies and their transformation of polystyrene‐block‐poly(4‐vinylpyridine) (PS‐b‐P4VP) in low‐alkanol solvents. In order to improve the solubility of polystyrene block in alcohol solvents, the solution of block copolymer sample was treated at a higher temperature, and then the influence of rate of decreasing temperature on multiple morphologies (including spheres, rods, vesicles, porous vesicles, large compound vesicles, and large compound micelles) was observed. The transformation of spheres to rods, to tyre‐shaped large compound micelles, and to sphere‐shaped large compound micelles was also realized. The formation mechanisms of the multiple morphologies and their transformation are discussed briefly.

Aggregates of PS‐P4VP formed in butanol by quenching from 110 °C to room temperature.