Temperature-Induced Morphological Transitions of Poly(dimethylacrylamide)–Poly(diacetone acrylamide) Block Copolymer Lamellae Synthesized via Aqueous Polymerization-Induced Self-Assembly

Aqueous dispersion polymerization of diacetone acrylamide (DAAM) by chain extension from a hydrophilic poly­(<i>N</i>,<i>N</i>-dimethyl­acrylamide) (PDMA₃₀) macromolecular chain transfer agent (macro-CTA) to produce PDMA₃₀–PDAAM_<i>x</i> block copolymer nano-objects was investigated in detail by systematically varying solids content and degree of polymerization of the core-forming PDAAM, leading to the formation of pure lamellae, mixed lamellae/vesicles, and pure vesicles as revealed by dynamic light scattering (DLS), transmission electron microscopy (TEM), atomic force microscopy (AFM), and scanning electron microscopy (SEM). PDMA₃₀–PDAAM_<i>x</i> lamellae were found to span an unprecedented wide space in the morphology phase diagram. Moreover, in situ cross-linking of lamellae via statistical copolymerization of DAAM with an asymmetric cross-linker allyl acrylamide and the effect of cross-linking density on the colloidal and morphological stabilities were studied, representing the first report on in situ cross-linking of lamellae during polymerization-induced self-assembly (PISA). Finally, reversible, temperature-induced morphological transitions from lamellae to worms/spheres on cooling were investigated by DLS, TEM, ¹H NMR spectroscopy, and rheology. The kinetics of the temperature-dependent morphological transitions and the rheological properties could be tuned by the cross-linking density

Photocontrolled RAFT Polymerization Mediated by a Supramolecular Catalyst

A photocontrolled reversible addition–fragmentation chain transfer (RAFT) polymerization mediated by a supramolecular photoredox catalyst is reported. Cucurbit[7]­uril (CB[7]) was used to form a host–guest complex with Zn­(II) meso-tetra­(4-naphthalylmethylpyridyl) porphyrin (ZnTPOR) to prevent aggregation of ZnTPOR, which in combination with a chain transfer agent (CTA) initiated efficient and controlled RAFT polymerization in water under visible light. RAFT polymerization was significantly affected by the subtle interplay of host–guest, electrostatic, and steric interactions among CB[7], ZnTPOR, and CTA. Polymerization rate was remarkably improved using CB[7]@ZnTPOR in comparison with that using ZnTPOR. The use of supramolecular interactions to modulate photocontrolled RAFT polymerization provides new opportunities to manipulate controlled radical polymerizations

Polymerization-Induced Cooperative Assembly of Block Copolymer and Homopolymer via RAFT Dispersion Polymerization

Polymerization-induced cooperative assembly (PICA) is developed to promote morphological transitions at high solids via RAFT dispersion polymerization, using both a macromolecular chain transfer agent (macro-CTA) and a small molecule chain transfer agent (CTA) to generate nano-objects consisting of well-defined block copolymer and homopolymer. PICA is demonstrated to promote morphological transitions under various conditions. Elemental mapping provides unambiguous evidence for the uniform distribution of the homopolymer within the core of the nano-objects. It is proposed that the growing homopolymer first reaches its solubility limit and forms aggregates, which induce the adsorption of the growing block copolymer. This effective and robust PICA approach significantly expands the capability to promote morphological transitions in RAFT dispersion polymerization and will facilitate the efficient synthesis of various higher-order morphologies at high solids

In Situ Cross-Linking of Vesicles in Polymerization-Induced Self-Assembly

In situ cross-linking of nano-objects with controllable morphologies in polymerization-induced self-assembly (PISA) has been a challenge because cross-linking lowers chain mobility and hence inhibits morphology transition. Herein, we propose a novel strategy that allows in situ cross-linking of vesicles in PISA in an aqueous dispersion polymerization formulation. This is realized by utilizing an asymmetric cross-linker bearing two vinyl groups of differing reactivities such that cross-linking is delayed to the late stage of polymerization when morphology transition has completed. Cross-linked vesicles with varying degrees (1–5 mol %) of cross-links were prepared, and their resistance to solvent dissolution and surfactant disruption was investigated. It was found that vesicles with ≥2 mol % cross-links were able to retain their structural integrity and colloidal stability when dispersed in DMF or in the presence of 1% of an anionic surfactant sodium dodecyl sulfate

Dual-Responsive [2]Pseudorotaxane On the basis of a pH-Sensitive Pillar[5]arene and Its Application in the Fabrication of Metallosupramolecular Polypseudorotaxane

Metallosupramolecular polymer, an appealing polymeric material, plays important roles in many fields including catalysis, electrochemical devices, conducting materials and so on. As a class of metallosupramolecular polymers, metallosupramolecular polypseudorotaxane has attracted great attention not only because of its wide applications but also due to its facile synthesis which is by metal coordination between metal and macrocycle-based pseudorotaxane. The introducing of stimuli-responsive property into the metallosupramolecular polypseudorotaxane system will enrich their functionality. Herein, a triple stimuli-responsive metallosupramolecular polypseudorotaxane constructed by pillararene-based host–guest interaction and copper coordination. First, a new pH-sensitive pillar[5]­arene host (<b>H</b>) was synthesized. An azastilbenzene derivative, <i>trans</i>- 4,4′-vinylenedipyridine (<i><b>trans</b></i>-<b>G</b>) was chosen as the guest molecule to construct a [2]­pseudorotaxane based on <b>H</b> and <i><b>trans</b></i>-<b>G</b>. The [2]­pseudorotaxane displayed pH- and photo- dual stimuli-responsiveness. Then the [2]­pseudorotaxane was used to construct a pH-, photo- and cyanide-triple stimuli-responsive metallosupramolecular polypseudorotaxane based on Cu­(II) ion coordination

Morphological Stabilization of Block Copolymer Worms Using Asymmetric Cross-Linkers during Polymerization-Induced Self-Assembly

Block copolymer worm stabilization via cross-linking during polymerization-induced self-assembly (PISA) is challenging. This is because block copolymer worms typically occupy a narrow regime in the phase diagram, and in situ cross-linking may hinder a morphological transition from sphere to worm. In this work, in situ cross-linking of block copolymer worms during PISA was studied using three different asymmetric cross-linkers, each bearing a pair of double bonds with different reactivities. Specifically, ethanolic PISA syntheses targeting poly­(2-(dimethyl­amino)­ethyl methacrylate)-<i>b</i>-poly­(benzyl methacrylate) diblock copolymer worms were investigated in the presence of vinyl methacrylate, allyl methacrylate, or 4-allyloxybenzyl methacrylate. The copolymerizations of benzyl methacrylate with the asymmetric cross-linkers underwent progressive branching to finally cross-linking of the block copolymer worms. While all the three asymmetric cross-linkers were able to cross-link worms, 4-allyloxybenzyl methacrylate with a structure mimicking benzyl methacrylate showed the best results with minimal perturbation to the worm morphology

In Situ Cross-Linking as a Platform for the Synthesis of Triblock Copolymer Vesicles with Diverse Surface Chemistry and Enhanced Stability via RAFT Dispersion Polymerization

An intrinsic dilemma exists for block copolymer vesiclesimproving the colloidal stability of vesicles using long/charged stabilizing blocks lowers the propensity of morphological transition to vesicles. Moreover, maintaining the vesicular morphology requires effective structure stabilization via cross-linking. We report a strategy to circumvent this problem and simultaneously improve the colloidal and structural stability of vesicles synthesized via polymerization-induced self-assembly (PISA) using dispersion polymerization. More specifically, in situ cross-linked poly­(<i>N</i>,<i>N</i>-dimethyl­acrylamide)-<i>b</i>-poly­(diacetone acrylamide-<i>co</i>-allylacrylamide) diblock copolymer vesicles are first synthesized via aqueous dispersion polymerization, which then serve as a robust platform to initiate the growth of a third hydrophilic block of either neutral poly­(<i>N</i>,<i>N</i>-dimethyl­acrylamide), anionic poly­(2-acrylamido-2-methyl-1-propane­sulfonic acid sodium salt), or cationic poly­(3-acrylamido­propyl trimethyl­ammonium chloride) with retained vesicular morphology. The formed cross-linked triblock copolymer vesicles have advantages of diverse surface chemistry and arbitrary stabilizing block length. As a control experiment, synthesis from linear diblock copolymer vesicles provides a mixture of triblock copolymer vesicles and spheres. The successful synthesis of triblock copolymer vesicles with a binary mixture of two hydrophilic stabilizing blocks is supported by dynamic light scattering (DLS), transmission electron microscopy (TEM), electrophoresis, and X-ray photoelectron spectroscopy (XPS). Both linear and cross-linked triblock copolymer vesicles are subjected to solvent dissolution, freeze-drying, and surfactant challenge studies, which collectively demonstrate that cross-linked triblock copolymers can maintain their vesicular structure and show excellent colloidal and structural stability, as indicated by DLS, TEM, and transmittance measurements

Dual-Responsive [2]Pseudorotaxane On the basis of a pH-Sensitive Pillar[5]arene and Its Application in the Fabrication of Metallosupramolecular Polypseudorotaxane

Metallosupramolecular polymer, an appealing polymeric material, plays important roles in many fields including catalysis, electrochemical devices, conducting materials and so on. As a class of metallosupramolecular polymers, metallosupramolecular polypseudorotaxane has attracted great attention not only because of its wide applications but also due to its facile synthesis which is by metal coordination between metal and macrocycle-based pseudorotaxane. The introducing of stimuli-responsive property into the metallosupramolecular polypseudorotaxane system will enrich their functionality. Herein, a triple stimuli-responsive metallosupramolecular polypseudorotaxane constructed by pillararene-based host–guest interaction and copper coordination. First, a new pH-sensitive pillar[5]­arene host (<b>H</b>) was synthesized. An azastilbenzene derivative, <i>trans</i>- 4,4′-vinylenedipyridine (<i><b>trans</b></i>-<b>G</b>) was chosen as the guest molecule to construct a [2]­pseudorotaxane based on <b>H</b> and <i><b>trans</b></i>-<b>G</b>. The [2]­pseudorotaxane displayed pH- and photo- dual stimuli-responsiveness. Then the [2]­pseudorotaxane was used to construct a pH-, photo- and cyanide-triple stimuli-responsive metallosupramolecular polypseudorotaxane based on Cu­(II) ion coordination

Biomimetic Microfluidic Device for in Vitro Antihypertensive Drug Evaluation

Microfluidic devices have emerged as revolutionary, novel platforms for in vitro drug evaluation. In this work, we developed a facile method for evaluating antihypertensive drugs using a microfluidic chip. This microfluidic chip was generated using the elastic material poly­(dimethylsiloxane) (PDMS) and a microchannel structure that simulated a blood vessel as fabricated on the chip. We then cultured human umbilical vein endothelial cells (HUVECs) inside the channel. Different pressures and shear stresses could be applied on the cells. The generated vessel mimics can be used for evaluating the safety and effects of antihypertensive drugs. Here, we used hydralazine hydrochloride as a model drug. The results indicated that hydralazine hydrochloride effectively decreased the pressure-induced dysfunction of endothelial cells. This work demonstrates that our microfluidic system provides a convenient and cost-effective platform for studying cellular responses to drugs under mechanical pressure

Dual-Responsive [2]Pseudorotaxane On the basis of a pH-Sensitive Pillar[5]arene and Its Application in the Fabrication of Metallosupramolecular Polypseudorotaxane

Metallosupramolecular polymer, an appealing polymeric material, plays important roles in many fields including catalysis, electrochemical devices, conducting materials and so on. As a class of metallosupramolecular polymers, metallosupramolecular polypseudorotaxane has attracted great attention not only because of its wide applications but also due to its facile synthesis which is by metal coordination between metal and macrocycle-based pseudorotaxane. The introducing of stimuli-responsive property into the metallosupramolecular polypseudorotaxane system will enrich their functionality. Herein, a triple stimuli-responsive metallosupramolecular polypseudorotaxane constructed by pillararene-based host–guest interaction and copper coordination. First, a new pH-sensitive pillar[5]­arene host (<b>H</b>) was synthesized. An azastilbenzene derivative, <i>trans</i>- 4,4′-vinylenedipyridine (<i><b>trans</b></i>-<b>G</b>) was chosen as the guest molecule to construct a [2]­pseudorotaxane based on <b>H</b> and <i><b>trans</b></i>-<b>G</b>. The [2]­pseudorotaxane displayed pH- and photo- dual stimuli-responsiveness. Then the [2]­pseudorotaxane was used to construct a pH-, photo- and cyanide-triple stimuli-responsive metallosupramolecular polypseudorotaxane based on Cu­(II) ion coordination