Synthesis, rapid responsive thickening, and self-assembly of brush copolymer poly(ethylene oxide)-graft-poly(N,N-dimethylaminoethyl methacrylate) in aqueous solutions

Loose Semirigid Aromatic Polyester Bottle Brushes at Poly(2-isopropyl-2-oxazoline) Side Chains of Various Lengths: Behavior in Solutions and Thermoresponsiveness

A polycondensation aromatic polyester with an oxygen spacer was synthesized and used as a macroinitiator for the grafting of linear poly(2-isopropyl-2-oxazoline) (PiPrOx) by the cationic polymerization method. The length of the thermosensitive side chains was varied by the initiator:monomer ratio. Using methods of molecular hydrodynamics, light scattering and turbidimetry, the copolymers were studied in organic solvents and in water. The molecular characteristics of the main chain and graft copolymers, the polymerization degree of side chains and their grafting density have been determined. The equilibrium rigidity of the macroinitiator and the conformations of grafted macromolecules were evaluated. In selective solvents, they take on a star-like conformation or aggregate depending on the degree of shielding of the main chain by side chains. The thermoresponsiveness of graft copolymers in aqueous solutions was studied, and their LCST were estimated. The results are compared with data for graft copolymers composed of PiPrOx side chains and flexible or rigid chain backbones of aromatic polyester type.

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.

Thermoresponsive Molecular Brushes with a Rigid-Chain Aromatic Polyester Backbone and Poly-2-alkyl-2-oxazoline Side Chains

A new polycondensation aromatic rigid-chain polyester macroinitiator was synthesized and used to graft linear poly-2-ethyl-2-oxazoline as well as poly-2-isopropyl-2-oxazoline by cationic polymerization. The prepared copolymers and the macroinitiator were characterized by NMR, GPC, AFM, turbidimetry, static, and dynamic light scattering. The molar masses of the polyester main chain and the grafted copolymers with poly-2-ethyl-2-oxazoline and poly-2-isopropyl-2-oxazoline side chains were 26,500, 208,000, and 67,900, respectively. The molar masses of the side chains of poly-2-ethyl-2-oxazoline and poly-2-isopropyl-2-oxazoline and their grafting densities were 7400 and 3400 and 0.53 and 0.27, respectively. In chloroform, the copolymers conformation can be considered as a cylinder wormlike chain, the diameter of which depends on the side chain length. In water at low temperatures, the macromolecules of the poly-2-ethyl-2-oxazoline copolymer assume a wormlike conformation because their backbones are well shielded by side chains, whereas the copolymer with short side chains and low grafting density strongly aggregates, which was visualized by AFM. The phase separation temperatures of the copolymers were lower than those of linear analogs of the side chains and decreased with the concentration for both samples. The LCST were estimated to be around 45 °C for the poly-2-ethyl-2-oxazoline graft copolymer, and below 20 °C for the poly-2-isopropyl-2-oxazoline graft copolymer.

Synthesis, Structure, Hydrodynamics and Thermoresponsiveness of Graft Copolymer with Aromatic Polyester Backbone at Poly(2-isopropyl-2-oxazoline) Side Chains

New thermoresponsive graft copolymers with an aromatic polyester backbone and poly(2-isopropyl-2-oxazoline) (PiPrOx) side chains are synthesized and characterized by NMR and GPC. The grafting density of side chains is 0.49. The molar masses of the graft-copolymer, its backbone, side chains, and the modeling poly-2-isopropyl-2-oxaziline are 74,000, 19,000, 4300, and 16,600 g·mol⁻¹, respectively. Their conformational properties in nitropropane as well as thermoresponsiveness in aqueous solutions are studied and compared with that of free side chains, i.e., linear PiPrOx with a hydrophobic terminal group. In nitropropane, the graft-copolymer adopts conformation of a 13-arm star with a core of a collapsed main chain and a PiPrOx corona. Similarly, a linear PiPrOx chain protects its bulky terminal group by wrapping around it in a selective solvent. In aqueous solutions at low temperatures, graft copolymers form aggregates due to interaction of hydrophobic backbones, which contrasts to molecular solutions of the model linear PiPrOx. The lower critical solution temperature (LCST) for the graft copolymer is around 20 °C. The phase separation temperatures of the copolymer solution were lower than that of the linear chain counterpart, decreasing with concentration for both polymers.

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.

Thermo-reversible sol–gel transition of aqueous solutions of patchy polymers

Aqueous solutions of an amphiphilic thermoreversible patchy polymer show abrupt gelation upon cooling by the combined effect of percolation and transition from intra to intermolecular hydrophobic associations.

Grafting of multi-sensitive PDMAEMA brushes onto carbon nanotubes by ATNRC: tunable thickening/thinning and self-assembly behaviors in aqueous solutions

Shear-induced thickening/thinning response of synthesized MWNTs-g-PDMAEMA suspensions was facially adjusted by altering the hydrophobic interaction, amount of f-PDMAEMA and grafted-chain length.

Multi-tunable self-assembled morphologies of stimuli-responsive diblock polyampholyte films on solid substrates

Intelligent polymers, due to their sensitive stimuli response to changes in the environment, have gained increasing amounts of attention over recent years and have become a popular topic in polymer materials science. In this study, the aggregation behaviors and stimuli responses of the stimuli-responsive diblock polyampholyte poly(2-(dimethylamino)ethyl methacrylate)-b-poly(acrylic acid) (PDMAEMA-b-PAA) are conveniently tunable by introducing pH changes, temperature changes, salt addition and surfactant neutralization. Under different pH values, either globular or fractal self-assemblies can be observed in which the latter have crystal properties. Salts and alkalis can promote the fractal aggregation growth because their deposited crystals can act as nucleation sites for the polyampholyte chains. A combination of fluorescence spectroscopy, atom force microscopy and transmission electron microscopy revealed that the presence of anionic surfactants in the PDMAEMA-b-PAA solutions promoted the solubility of the polyampholyte, consequently leading to a more homogeneous distribution of the polymer chains on the solid substrate upon drying the mixtures. The fractal formation was suppressed for the studied Gemini surfactants, and a higher surfactant hydrophobicity results in an earlier start of the formation of the fractal pattern.

Liquid marbles prepared from pH-responsive self-assembled micelles

In this study, we report the assembly of amphiphilic polymeric micelles at the liquid/air interface to prepare liquid marbles for the first time. The polymeric micelles were synthesized from the self-assembly of a fluoropolymer, poly(styrene-co-acrylic acid-co-2,2,3,4,4,4-hexafluorobutyl methacrylate), in a selective solvent. The particle size, morphology and chemical composition of the micelles were determined by dynamic light scattering (DLS), transmission electron microscopy, scanning electron microscopy and X-ray photoelectron spectroscopy. DLS and aqueous electrophoresis revealed the pH-responsiveness of the micelles in aqueous dispersion. Liquid marbles with water volumes varying from 10 μL to 1 mL were formed by rolling water droplets on the micelle powder bed. The increase in water volume led to the shape transition of the liquid marbles from quasi-spherical to a puddle-like shape because of gravity. Fluorescence microscopy was used to observe the morphology of the formed liquid marbles, which confirmed that the micelles were adsorbed at the interface of water and air. The effective surface tension of the liquid marbles decreased with the increasing concentration of NaOH, which was added to the interior water phase. This agreed with the results of droplet roller experiments: the mechanical integrity of the liquid marbles prepared from alkaline solution (pH 10) was relatively poorer than those prepared from acidic solution (pH 2). Moreover, these liquid marbles coated with micelles showed pH-responsiveness when transferred onto the surfaces of aqueous solutions with different pH values. The liquid marbles were relatively stable on the acidic solution, whereas they burst immediately on the alkaline solution with a pH of 10. In addition, apart from water, Gellan gum solution and glycerol could be also successfully encapsulated by the fluorinated micelles to form stable liquid marbles.

UCST behavior of polyampholytes based on stoichiometric RAFT copolymerization of cationic and anionic monomers

Polyampholytes with controlled equimolar ratio of charges were synthesized by reversible addition–fragmentation chain transfer (RAFT) copolymerization of cationic and anionic monomers and their UCST behavior is reported.

Thermo and pH dual-controlled charge reversal amphiphilic graft copolymer micelles for overcoming drug resistance in cancer cells

A novel thermo and pH dual-controlled charge reversal PSMA₈₉-g-P(DMA₁₆-co-SD₅₆) graft copolymer micelle was developed with effectively enhanced cellular uptake for overcoming multi-drug resistance in cancer cells.

Nanohybrids from direct chemical self-assembly of poly(styrene-alt-maleic anhydride) as pH-responsive particulate emulsifiers

The nanohybrid particulate emulsifiers based on poly(styrene-alt-maleic anhydride) (SMA) were facilely prepared via the direct chemical self-assembly triggered by the aminolysis of SMA with 3-aminopropyltriethoxysilane (APTES) and the in situ polycondensation of APTES under refluxing in acetone. Transmission electron microscopy and scanning electron microscopy confirmed the spherical-like morphology of the nanohybrids. Dynamic light scattering and electrophoresis revealed the structure transition of the nanohybrids in response to pH change. The emulsification study showed that the nanohybrids were effective particulate emulsifiers when homogenized with various oils including toluene, paraffin oil, silicone oil, isooctyl palmitate, dicaprylyl carbonate, and propylheptyl caprylate. The nanohybrid particulate emulsifiers exhibited pH-sensitivity, and the diameter of paraffin oil droplets remarkably increased with pH of the nanohybrid aqueous dispersion decrease. Also, the reduced dynamic interfacial tension predicted the thermodynamically unstable state of the emulsions prepared at high pH values. Most interesting, the paraffin oil-in-water high internal phase emulsions (HIPEs) with a high oil volume fraction of 83.3% were formed when the nanohybrids were heavily flocculated by adding HCl. The HIPEs were pH-responsive and capable of demulsification with the addition of an alkaline solution showing a potential application in the oil industry.

Effect of composition of PDMAEMA-b-PAA block copolymers on their pH- and temperature-responsive behaviors

A series of poly(2-(dimethylamino) ethyl methacrylate) (PDMAEMA) homopolymers and poly(2-(dimethylamino)ethyl methacrylate)-b-poly(acrylic acid) (PDMAEMA-b-PAA) diblock copolymers were synthesized by atomic transfer radical polymerization. Thanks to a fine-tuning of the hydrophobic-hydrophilic balance by varying the molecular weight of the polymers and the pH of the aqueous solutions, as well as the composition for the block copolymers, the lower critical solution temperature (LCST) and the aggregation-dissolution kinetics of PDMAEMA homopolymers and PDMAEMA-b-PAA block copolymers can be adjusted. For the block copolymers, the results show that larger relative size of the PDMAEMA blocks leads to an increasing tendency to form micellar aggregates and a decrease of the LCST of the aqueous solution, which is consistent with the increasing copolymer hydrophobicity. A significant difference of the stimuli-responsive behavior between PDMAEMA-rich and PAA-rich copolymers is observed, because the former exhibit thermo-responsive behavior in a broad temperature range of 40-60 °C in basic media, while the pH-responsive behavior is dominant, and only a weak thermo-responsive behavior is exhibited around the specific isoelectric point (IEP) in the latter case. The aggregation rate is strongly influenced by temperature, molecular weight, structure, and composition of the polymer. Specifically, temperature has a stronger effect than the molar ratio of the PDMAEMA segment in the copolymer (related to its hydrophobicity) and the chain molecular weight, although the PDMAEMA-b-PAA copolymers show faster aggregation rate than do the PDMAEMA homopolymers.

Tailoring polymeric micelles to optimize delivery to solid tumors

Block copolymer micelles have shown great potential in drug delivery systems, not only for overcoming the drawbacks of small agents such as water insolubility and wide distribution in normal tissues, but also for avoiding traditional nanoparticle formulation shortcomings, including in vivo instability and fast clearance from the blood. However, for translating micellar formulations to clinical practice, it is essential to overcome the many in vivo obstacles. Surmounting these barriers strongly depends on micellar physicochemical properties, which can be further optimized by the unique physiological aspects of solid tumors such as low pH, high temperature and the presence of abnormal vessels. Herein, based on the Flory parameter and scaling theory, the fundamental mechanisms and correlations in vitro/in vivo between self assembly, drug loading and release, stability, intracellular delivery and in vivo distribution, as well as micellar composition, size and microstructural tailoring are systematically revisited. The methods for enhancing micellar performance in solid tumors were consequently proposed through well-defined core-corona structure tailoring.