Thermosensitive Polymer-Modified Mesoporous Silica for pH and Temperature-Responsive Drug Delivery

A mesoporous silica-based drug delivery system (MS@PNIPAm-PAAm NPs) was synthesized by conjugating the PNIPAm-PAAm copolymer onto the mesoporous silica (MS) surface as a gatekeeper that responds to temperature and pH changes. The drug delivery studies are carried out in vitro at different pH (7.4, 6.5, and 5.0) and temperatures (such as 25 °C and 42 °C, respectively). The surface conjugated copolymer (PNIPAm-PAAm) acts as a gatekeeper below the lower critical solution temperature (LCST) (<32 °C) and as a collapsed globule structure above LCST (>32 °C), resulting in controlled drug delivery from the MS@PNIPAm-PAAm system. Furthermore, the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay and cellular internalization results support the prepared MS@PNIPAm-PAAm NPs being biocompatible and readily taken up by MDA-MB-231 cells. The prepared MS@PNIPAm-PAAm NPs, with their pH-responsive drug release behavior and good biocompatibility, could be used as a drug delivery vehicle where sustained drug release at higher temperatures is required.

Double hydrophilic copolymers - synthetic approaches, architectural variety, and current application fields

Solubility and functionality of polymeric materials are essential properties determining their role in any application. In that regard, double hydrophilic copolymers (DHC) are typically constructed from two chemically dissimilar but water-soluble building blocks. During the past decades, these materials have been intensely developed and utilised as, e.g., matrices for the design of multifunctional hybrid materials, in drug carriers and gene delivery, as nanoreactors, or as sensors. This is predominantly due to almost unlimited possibilities to precisely tune DHC composition and topology, their solution behavior, e.g., stimuli-response, and potential interactions with small molecules, ions and (nanoparticle) surfaces. In this contribution we want to highlight that this class of polymers has experienced tremendous progress regarding synthesis, architectural variety, and the possibility to combine response to different stimuli within one material. Especially the implementation of DHCs as versatile building blocks in hybrid materials expanded the range of water-based applications during the last two decades, which now includes also photocatalysis, sensing, and 3D inkjet printing of hydrogels, definitely going beyond already well-established utilisation in biomedicine or as templates.

Polymer Brushes: Efficient Synthesis and Applications

Polymer brushes are special macromolecular structures with polymer chains densely tethered to another polymer chain (one-dimensional, 1D) or the surface of a planar (two-dimensional, 2D), spherical or cylindrical (three-dimensional, 3D) solid via a stable covalent or noncovalent bond linkage. In comparison with the corresponding linear counterpart with similar molecular composition, one-dimension polymer brushes have some fascinating properties including wormlike conformation, compact molecular dimension, and notable chain end effects due to their compact and confined densely grafted structure. The introduction of polymer chains onto the surface of planar and spherical or cylindrical matrix will not only significantly change the surface-related properties of the matrix but also endows the obtained hybrid polymer brushes with new functionalities. Thus, polymer brushes are of great interest in the fields of polymer and material science due to their broad applications, such as catalysis, nanolithography, biomineralization, drug delivery, medical diagnosis, optoelectronics, and so on. Although a variety of 1D, 2D, and 3D polymer brushes have been prepared with the advent of living/controlled polymerization, the development of more efficient and facile synthetic protocols that permit access to polymer brushes with precisely controlled composition, structure, and functionality still represents a key contemporary challenge. In this Account, we summarize our recent efforts on the development of efficient methods to prepare 1D, 2D, and 3D polymer brushes and exploration of their potential applications in drug delivery, antifouling coating, catalysis, and lithium-ion batteries and also highlight related achievements by other groups. First, we briefly introduce the precedent examples of efficient synthesis of polymer brushes with different structures and functionalities by the combination of monomer design with living/controlled polymerization. Given the excellent tolerance and use of the same catalytic system without any mutual interference of ATRP and Cu-catalyzed alkyne-azide cyclization (CuAAC) click reaction, a versatile and efficient platform for precise synthesis of complex asymmetric (Janus-type) 1D polymer brushes was developed on the basis of the "trifunctional monomer" strategy without polymeric functionality transformation. Subsequently, a noncovalent strategy based on crystallization-driven self assembly to prepare well-defined polymer brushes with precise control over their composition and dimensions is described. Notably, the crystallization-driven self assembly can be treated as a living/controlled polymerization of "polymeric monomer" with a special building segment for crystallization, which allows for preparing linear polymer brushes with length as high as tens of micrometers. Moreover, the properties and related applications of polymer brushes as interesting building blocks for constructing hierarchical nanostructures, efficient drug deliver carriers, antifouling films, and lithium-ion batteries are addressed by some typical examples. These advancements in this field will provide a new avenue for obtaining fascinating polymer-brush-based functional materials.

Self-assembly/disassembly of giant double-hydrophilic polymersomes at biologically-relevant pH

Self-assembled giant polymer vesicles prepared from double-hydrophilic diblock copolymers, poly(ethylene oxide)-b-poly(acrylic acid) (PEO-PAA) show significant degradation in response to pH changes. Because of the switching behavior of the diblock copolymers at biologically-relevant pH environments (2 to 9), these polymer vesicles have potential biomedical applications as smart delivery vehicles.

pH-Responsive polymers

This review summarizes pH-responsive monomers, polymers and their derivative nano- and micro-structures including micelles, cross-linked micelles, microgels and hydrogels.

An efficient route to synthesize thermoresponsive molecular bottlebrushes of poly[o-aminobenzyl alcohol-graft-poly(N-isopropylacrylamide)]

The thermoresponsive molecular bottlebrushes of poly[o-aminobenzyl alcohol-graft-poly(N-isopropylacrylamide)] [P(oABA-g-PNIPAM)] were synthesized and their characteristic thermoresponse was demonstrated.

A Critical Appraisal of RAFT-Mediated Polymerization-Induced Self-Assembly

Recently, polymerization-induced self-assembly (PISA) has become widely recognized as a robust and efficient route to produce block copolymer nanoparticles of controlled size, morphology, and surface chemistry. Several reviews of this field have been published since 2012, but a substantial number of new papers have been published in the last three years. In this Perspective, we provide a critical appraisal of the various advantages offered by this approach, while also pointing out some of its current drawbacks. Promising future research directions as well as remaining technical challenges and unresolved problems are briefly highlighted.

First double hydrophilic graft copolymer bearing a poly(2-hydroxylethyl acrylate) backbone synthesized by sequential RAFT polymerization and SET-LRP

This article reports the first synthesis of well-defined double hydrophilic graft copolymers with a PHEA backbone, by the combination of RAFT polymerization, SET-LRP, and a grafting-from strategy.

Disorder to Order Transition and Ordered Morphology of Coil-Comb Block Copolymer by Self-Consistent Field Theory

The disorder to order transition and the ordered patterns near the disordered state of coil-comb copolymer A-b-(B m + 1-g-C m ) are investigated by the self-consistent field theory. The phase diagrams of coil-comb copolymer are obtained by varying the composition of the copolymer with the side chain number m = 1, 2, and 3. The disorder to order transition is far more complex compared with the comb copolymer or linear block copolymer. As the side chain number m increases, the Flory-Huggins interaction parameter of disorder to order transition (DOT) increases and the lowest DOT occurs when the volume fractions of blocks A, B, and C are approximately equal. When one component is the minority, the disorder to order transition curve is similar with binary copolymer, but the curve shows the asymmetric property. The comb copolymer is more stable with larger side chain number m and shorter side chain. The ordered patterns from the disordered state are discussed. The results are helpful for designing coil-comb copolymers and obtaining the ordered morphology.

Aqueous copper(0) mediated reversible deactivation radical polymerization of 2-hydroxyethyl acrylate

Lowering the concentration of adsorbed radicals on the Cu(0) surface, achieved by reducing catalyst and adding NaBr, is the key to the synthesis of well-defined P(HEA) without a high molecular weight shoulder in aqueous solution using two-step Cu(0) in situ mediation.

Reversible deactivation radical polymerization in the presence of zero-valent metals: from components to precise polymerization

We highlight recent work from the advent of zero-valent metal-mediated RDRP looking at advances in its components and the synthesis of well-defined polymers.

Smart assembly behaviors of hydroxypropylcellulose-graft-poly(4-vinyl pyridine) copolymers in aqueous solution by thermo and pH stimuli

Thermo- and pH-sensitive graft copolymers, hydroxypropylcellulose-graft-poly(4-vinyl pyridine) (HPC-g-P4VP), were synthesized via atom transfer radical polymerization (ATRP) and characterized. The thermo- and pH-induced micellization and stimuli-responsive properties of HPC-g-P4VP graft copolymers in aqueous solution were investigated by transmittance, (1)H NMR, dynamic light scattering (DLS), and so on. For the pH-induced micellization, the P4VP side chains collapse to form the core of the micelles, and the HPC backbones stay in the shell to stabilize the micelles. In the case of thermoinduced micellization, the HPC backbones collapse to form the core of the micelles that was stabilized by the P4VP side chains in the shell upon heating. What's more, the cloud point of the HPC-g-P4VP copolymers in the aqueous solution could be finely tuned by changing the length of P4VP side chains or the pH values. In acidic water, the longer the side chains, the higher the cloud point. For those HPC-g-P4VP copolymers with short side chains, for example, HPC0.05-g-P4VP(3), the lower pH correlates a higher cloud point. The thermo- or pH-induced micelles also have the pH- or thermosensitivity due to their P4VP or HPC shells.

pH-responsive supramolecular self-assembly of well-defined zwitterionic ABC miktoarm star terpolymers

We report the first example of the synthesis and pH-responsive supramolecular self-assembly of double hydrophilic ABC miktoarm star terpolymers. Well-defined ABC miktoarm star terpolymers consisting of poly(ethylene glycol), poly(tert-butyl methacrylate), and poly(2-(diethylamino)ethyl methacrylate) arms [PEG(-b-PtBMA)-b-PDEA] were synthesized via the combination of consecutive click reactions and atom transfer radical polymerization (ATRP), starting from a trifunctional core molecule, 1-azido-3-chloro-2-propanol (ACP). The click reaction of monoalkynyl-terminated PEG with an excess of ACP afforded difunctional PEG bearing a chlorine and a secondary hydroxyl moiety at the chain end, PEG113(-Cl)-OH (1). After azidation with NaN3, PEG-based macroinitiator PEG113(-N3)-Br (3) was prepared by the esterification of PEG113(-N3)-OH (2) with 2-bromoisobutyryl bromide and then employed in the ATRP of tert-butyl methacrylate (tBMA). The obtained PEG(-N3)-b-PtBMA copolymers (4) possessed an azido moiety at the diblock junction point. The preparation of PEG(-b-PtBMA)-b-PDEA miktoarm star terpolymers was then achieved via the click reaction of 4 with an excess of monoalkynyl-terminated PDEA. The obtained miktoarm star terpolymers were successfully converted into PEG(-b-PMAA)-b-PDEA, where PMAA is poly(methacrylic acid). In aqueous solution, PEG(-b-PMAA)-b-PDEA zwitterionic ABC miktoarm star terpolymers can self-assemble into three types of micellar aggregates by simply adjusting solution pH at room temperature. Above pH 8, PDEA-core micelles stabilized by PEG/ionized PMAA hybrid coronas were formed due to the insolubility of PDEA block. In the range of pH 5-7, micelles possessing polyion complex cores formed as a result of charge compensation between partially ionized PMAA and partially protonated PDEA sequences. At pH<4, hydrogen bonding interactions between fully protonated PMAA and PEG led to the formation of another type of micellar aggregates possessing hydrogen-bonded complex cores stabilized by protonated PDEA coronas. The fully reversible pH-responsive formation of three types of aggregates were characterized by 1H NMR, dynamic and static laser light scattering (LLS), and transmission electron microscopy (TEM).

Redox, Ionic Strength, and pH Sensitive Supramolecular Polymer Assemblies

Supramolecular complex of a cationic surfactant and oppositely charged disulfide containing polyelectrolyte was found to form micelle type aggregates at concentration much lower than the critical aggregate concentration (CAC) of the surfactant itself. We show that this difference can be utilized to generate stimulus-sensitive disassembly of these structures. This can be achieved either by converting the polyelectrolyte counterions to monovalent counterions in response to a stimulus or by simply weakening the interaction between the polymer and the surfactant in the presence of a stimulus. We have utilized three different stimuli to demonstrate these possibilities.