Block Copolymers In Aqueous Solution Research Articles

Exploring the impact of cresols on aggregation characteristics of non-linear PEO-PPO-PEO block copolymers in aqueous solution

The present research investigates the intricate interplay between some industrially essential compounds, viz. 2-methylphenol (o-cresol, OC), 4-methylphenol (p-cresol, PC), 4-n-Butylphenol (BP) and non-linear ethylene oxide-propylene oxide (EO-PO) type block copolymers (Tetronics®) in aqueous solutions by employing an array of physico-chemical techniques. Each examined Tetronic® possesses 40% EO segments in its molecular structure. The study delves into the interaction and structural modifications that occur when cresols are doped into the copolymer solutions. The added cresols disrupt the hydrophilic-hydrophobic balance of Tetronics® depending on their hydrophobicities. The lowering of the cloud point (CP) is accompanied by a corresponding increase in solution viscosity. Doping of OC and PC has a dissimilar effect on viscosity compared to BP. The intermicellar interactions are adjudged to be probable cause of the unusual viscosity trend. Scattering techniques (DLS and SANS) confirm the morphology of aggregates. The results are interpreted in terms of H-bonding.

Molecular Simulation Study of the Kinetics and Mechanism of Micellization of Charged and Uncharged Block Copolymer in Aqueous Solution: Polystyrene-Block-Poly(acrylic acid) PS-b-PAA

The micellization kinetics, dynamics, and diffusional properties of poly(styrene)-block-poly(acrylic acid) copolymer chains in salt-free aqueous solution have been investigated as a function of the copolymer composition (XPS ) for the cases of un-ionized (charge density f = 0) and ionized PAA blocks (charge density f = 1), for the first time to our knowledge via atomistic molecular dynamic simulations. The micelle formation mechanism was inspected by tracking the population of unimers and clusters across the simulation trajectory; it confirmed that the asymmetric copolymer micelle formation followed a combined approach of unimer insertion and cluster fusion mechanisms, while symmetric micelle formation followed the unimer insertion method exclusively. Micelle formation took a longer time for copolymers having charged (ionized) PAA blocks (f > 0) and relatively short PS blocks (number fraction of PS repeat units in copolymer XPS < 0.5) due to the presence of a greater number of hydrophobic groups, in agreement with the micellization kinetics observed for model copolymer micelles via DPD (Dissipative Particle Dynamics) simulation studies in literature. The conformational dynamics were studied using the relaxation of backbone dihedral angles and radius of gyration, for the core and corona blocks, respectively, showed that the PS blocks relaxed slower as compared to the soluble PAA blocks in solution due to their hydrophobic nature. The conformational relaxation time increased linearly for the PS blocks and was invariant for the PAA blocks with respect to XPS. The interaction dynamics of the PS-b-PAA copolymer micelles studied via the relaxation times of the PAA-PAA inter-chain (τHB,PP) and PAA-water inter-molecular hydrogen bonds (τHB,PW) showed the increase of τHB,PP, and the decrease of τHB,PW in solution with the increase in XPS. The PAA-water H-bond relaxes slower at f = 1 than that at f = 0 due to the stronger affinity of ionized PAA units with water molecules. The diffusivity of the copolymer chains decreased exponentially with an increase in XPS value, which is in agreement with the theoretical and experimental observations described in the literature.

Current paradigms in employing self-assembled structures: Drug delivery implications with improved therapeutic potential

Recent efforts have focused on developing improved drug delivery systems with enhanced therapeutic efficacy and minimal side effects. Micelles, self-assembled from amphiphilic block copolymers in aqueous solutions, have gained considerable attention for drug delivery. However, there is a need to further enhance their efficiency. These micelles offer benefits like biodegradability, biocompatibility, sustained drug release, and improved patient compliance. Yet, researchers must address stability issues and reduce toxicity. Nanoscale self-assembled structures have shown promise as efficient drug carriers, offering an alternative to conventional methods. Fine-tuning at the monomeric and molecular levels, along with structural modifications, is crucial for optimal drug release profiles. Various strategies, such as entrapping hydrophobic drugs and using polyethylene oxide diblock copolymer micelles to resist protein adsorption and cellular adhesion, protect the hydrophobic core from degradation. The polyethylene oxide corona also provides stealth properties, prolonging blood circulation for extended drug administration. Amphiphilic copolymers are attractive for drug delivery due to their adjustable properties, allowing control over micelle size and morphology. Emerging tools promise complex and multifunctional platforms. This article summarizes about the challenges as far as the use of micelles is concerned, including optimizing performance, rigorous pre-clinical and clinical research, and suggests further improvement for drug delivery efficacy.

Double Stimuli-Responsive di- and Triblock Copolymers of Poly(N-isopropylacrylamide) and Poly(1-vinylimidazole): Synthesis and Self-Assembly.

For the first time, double stimuli-responsive properties of poly(N-isopropylacrylamide) (PNIPA) and poly(1-vinylimidazole) (PVIM) block copolymers in aqueous solutions were studied. The synthesis of PNIPA60-b-PVIM90 and PNIPA28-b-PVIM62-b-PNIPA29 was performed using reversible addition-fragmentation chain transfer (RAFT) polymerization. The polymers were characterized by size exclusion chromatography and 1H NMR spectroscopy. The conformational behavior of the polymers was studied using dynamic light scattering (DLS) and fluorescence spectroscopy (FS). It was found that PNIPA and block copolymers conformation and ability for self-assembly in aqueous medium below and above cloud point temperature depend on the locus of hydrophobic groups derived from the RAFT agent within the chain. Additionally, the length of PVIM block, its locus in the chain and charge perform an important role in the stabilization of macromolecular micelles and aggregates below and above cloud point temperature. At 25 °C the average hydrodynamic radius (Rh) of the block copolymer particles at pH 3 is lower than at pH 9 implying the self-assembling of macromolecules in the latter case. Cloud points of PNIPA60-b-PVIM90 are ~43 °C and ~37 °C at a pH of 3 and 9 and of PNIPA28-b-PVIM62-b-PNIPA29 they are ~35 °C and 31 °C at a pH of 3 and 9. Around cloud point independently of pH, the Rh value for triblock copolymer rises sharply, achieves the maximum value, then falls and reaches the constant value, while for diblock copolymer, it steadily grows after reaching cloud point. The information about polarity of microenvironment around polymer obtained by FS accords with DLS data.

Aggregation Behavior of Nonsymmetrically End-Capped Thermoresponsive Block Copolymers in Aqueous Solutions: Between Polymer Coils and Micellar States

Aggregation Behavior of Nonsymmetrically End-Capped Thermoresponsive Block Copolymers in Aqueous Solutions: Between Polymer Coils and Micellar States

Effect of the macromolecular architecture on the thermoresponsive behavior of poly(N-isopropylacrylamide) in copolymers with poly(N,N-dimethylacrylamide) in aqueous solutions: Block vs random copolymers

Three samples from each type of poly(N-isopropylacrylamide)-block-poly(N,N-dimethylacrylamide) (PNIPAM-b-PDMA) block copolymers and poly(N-isopropylacrylamide-co-N,N-dimethylacrylamide) (P(NIPAM-co-DMA)) random copolymers with similar chemical composition were synthesized by RAFT polymerization. The effects of DMA on the thermoresponse of its two kinds of copolymers with NIPAM were comparatively investigated by turbidity analysis, variable-temperature 1H NMR and dynamic light scattering with PNIPAM homopolymer as a control. It was discovered that the phase transition temperature, the temperature response window and the hysteresis values of the PNIPAM-b-PDMA and P(NIPAM-co-DMA) counterpart were significantly different. In particular, the temperature response window, which represents the sensitivity of response, is smaller for random copolymers than that of block copolymers in aqueous solution, indicating that the temperature response of random copolymers is more sensitive than that of block copolymers. The possible reasons leading to different thermo-responsive phase transition characteristics between block copolymers and random copolymers are discussed, and the formation of different hydrophobic structures with the temperature increasing is ascribed.

Thermoresponsive Self-Assembly of Twofold Fluorescently Labeled Block Copolymers in Aqueous Solution and Microemulsions.

A nonionic double hydrophilic block copolymer with a long permanently hydrophilic and a small thermoresponsive block is synthesized by reversible addition-fragmentation chain-transfer polymerization (RAFT). By employing a specifically designed chain-transfer agent, the polymer is functionalized with complementary end groups which are suited for Förster resonance energy transfer (FRET). The end group attached to the permanently hydrophilic block of poly(N,N-dimethylacrylamide) pDMAm is designed as a permanently hydrophobic segment ("sticker") comprising a long alkyl chain and the 4-aminonaphthalimide fluorophore. The other end attached to the thermoresponsive block of poly(N-isopropylacrylamide) pNiPAm incorporates a coumarin fluorophore. The temperature-dependent self-assembly of the twofold fluorescently labeled copolymer is studied in pure aqueous solution as well as in an o/w microemulsion by several techniques including turbidimetry, dynamic light scattering (DLS), and fluorescence spectroscopy. It is compared to the behaviors of the analogous twofold-labeled pDMAm and pNiPAm homopolymer references. The findings indicate that the block copolymer behaves as a polymeric surfactant at low temperatures, with one relatively small hydrophobic end block and an extended hydrophilic chain forming "hairy micelles". At elevated temperatures above the LCST phase transition of the pNiPAm block, however, the copolymer behaves as an associative telechelic polymer with two nonsymmetrical hydrophobic end blocks, which do not mix. Thus, instead of a network of bridged "flower micelles", large dynamic aggregates are formed. These are connected alternatingly by the original micellar cores as well as by clusters of the collapsed pNiPAm blocks. This type of structure is even more favored in the o/w microemulsion than in pure aqueous solution, as the microemulsion droplets constitute an attractive anchoring point for the hydrophobic dodecyl sticker but not for the collapsed pNiPAm chains.

Effects of Polymer Block Length Asymmetry and Temperature on the Nanoscale Morphology of Thermoresponsive Double Hydrophilic Block Copolymers in Aqueous Solutions

By complementing small-angle neutron scattering (SANS) with Fourier transform infrared (FTIR) spectroscopy measurements, the influence of temperature as an external stimulus and block length asymmetry is studied on nanoscale assemblies of thermoresponsive double hydrophilic block copolymers in aqueous solutions. Morphologies and molecular hydration characteristics of two poly(N-isopropylacrylamide)-block-poly(oligo ethylene glycol methyl ether acrylate) (PNIPAM-b-POEGA) diblock copolymers, which differ in the length of the PNIPAM block, are compared. SANS provides insights into the nanostructure of the assemblies and FTIR probes vibrations of selected functional groups at the molecular level. Upon temperature increase, the solutions undergo transformations from hierarchical assemblies to more well-defined spherical morphologies. Variations in the block lengths lead to distinct morphological transformations. The variable morphological transformations originate from differences in the strength and/or amount of hydrogen bonding and hydrophobic interactions, as well as the chain density in the clusters formed and hydration. We identify transformations from hierarchical structures to fractal core–shell morphologies in the asymmetric block copolymer with the long PNIPAM block, while spherical and core–shell spherical morphologies are formed for the symmetric diblock copolymer with the short PNIPAM block. In these assemblies of PNIPAM-b-POEGA with the short PNIPAM block, the methyl side group hydration sensitively depends on the temperature increase at temperatures even beyond the nominal volume phase transition temperature. For both blocks, the evolution of the amide I band reflects that solvent–polymer interactions are still favorable even at the highest temperatures. Morphological variations after cooling to ambient temperature are reflected in both SANS and FTIR, pointing to remnant hydrogen bond interactions.

Dendritic Macromolecular Architectures: Dendrimer-Based Polyion Complex Micelles.

Polymeric micelles are nanoassemblies that are formed by spontaneous arrangement of amphiphilic block copolymers in aqueous solutions at critical micelle concentration (CMC). They represent an effective system for drug delivery of, for instance, poorly water-soluble anticancer drugs. Then, the development of polyion complexes (PICs) were emphasized. The morphology of these complexes depends on the topology of the polyelectrolytes used and the way they are assembled. For instance, ionic-hydrophilic block copolymers have been used for the preparation of PIC micelles. The main limitation in the use of PIC micelles is their potential instability during the self-assembly/disassembly processes, influenced by several parameters, such as polyelectrolyte concentration, deionization associated with pH, ionic strength due to salt medium effects, mixing ratio, and PIC particle cross-linking. To overcome these issues, the preparation of stable PIC micelles by increasing the rigidity of their dendritic architecture by the introduction of dendrimers and controlling their number within micelle scaffold was highlighted. In this original concise Review, we will describe the preparation, molecular characteristics, and pharmacological profile of these stable nanoassemblies.

Polymer directed synthesis of NiO nanoflowers to remove pollutant from wastewater

Nickel oxide (NiO) nanoflowers are synthesized via a one-pot method using an amphiphilic block copolymer in aqueous solution. Pluronics F-127 block copolymer works as a structure-directing agent in the formation of the NiO nanoflowers. The controlled hydrolysis of the precipitating agent slowly releases ammonia that can form Ni(OH)2, which is stabilized in the polymer solution. The calcination removes the polymeric part of the nanocomposite and converts Ni(OH)2 into NiO with a face-centered cubic (FCC) phase. The synthesized NiO nanoflowers possess a mesoporous structure with an average surface area of 154 m2/g. Physisorption and electrostatic interactions between negatively charged congo red (CR) and positively charged NiO nanoflowers allow the adsorption of CR dye at ambient conditions. The adsorption of dyes follows pseudo-second-order kinetics, and the adsorbents are regenerated by calcination and recycled three times at similar efficiencies.

Thermoinduced Crystallization-Driven Self-Assembly of Bioinspired Block Copolymers in Aqueous Solution.

Delicate control over architectures via crystallization-driven self-assembly (CDSA) in aqueous solution, particularly combined with external stimuli, is rare and challenging. Here, we report a stepwise CDSA process thermally initiated from amphiphilic poly(N-allylglycine)-b-poly(N-octylglycine) (PNAG-b-PNOG) conjugated with thiol-terminated triethylene glycol monomethyl ethers ((PNAG-g-EG3)-b-PNOG) in aqueous solution. The diblock copolymers show a reversible thermoresponsive behavior with nearly identical cloud points in both heating and cooling runs. In contrast, the morphology transition of the assemblies is irreversible upon a heating-cooling cycle because of the presence of a confined domain arising from crystalline PNOG, which allows for the achievement of different nanostructured assemblies by the same polymer. We demonstrated that the thermoresponsive property of PNAG-g-EG3 initiates assembly kinetically that is subsequently promoted by crystallization of PNOG thermodynamically. The irreversible morphology transition behavior provides a convenient platform for comparing the cellular uptake efficiency of nanostructured assemblies with various morphologies that are otherwise similar.

Sequential Self-Assembly Using Tannic Acid and Phenylboronic Acid-Modified Copolymers for Potential Protein Delivery.

Tannic acid (TA) can form stable complexes with proteins, attracting significant attention as protein delivery systems. However, its systemic application has been limited due to nonspecific interaction. Here, we report a simple technique to prepare systemically applicable protein delivery systems using sequential self-assembly of a protein, TA, and phenylboronic acid-conjugated PEG-poly(amino acid) block copolymers in aqueous solution. Mixing the protein and TA in aqueous solution led to covering of the protein with TA, and subsequent addition of the copolymer resulted in the formation of boronate esters between TA and copolymers, constructing the core-shell-type ternary complex. The ternary complex covered with PEG exhibited a small hydrodynamic diameter of ∼10-20 nm and prevented an unfavorable interaction with serum components, thereby accomplishing significantly prolonged blood circulation and enhanced tumor accumulation in a subcutaneous tumor model. The technique utilizing supramolecular self-assembly may serve as a novel approach for designing protein delivery systems.

Synthesis and Self-Assembly of Poly(N-Vinylcaprolactam)-b-Poly(ε-Caprolactone) Block Copolymers via the Combination of RAFT/MADIX and Ring-Opening Polymerizations.

Well-defined amphiphilic, biocompatible and partially biodegradable, thermo-responsive poly(N-vinylcaprolactam)-b-poly(ε-caprolactone) (PNVCL-b-PCL) block copolymers were synthesized by combining reversible addition-fragmentation chain transfer (RAFT) and ring-opening polymerizations (ROP). Poly(N-vinylcaprolactam) containing xanthate and hydroxyl end groups (X–PNVCL–OH) was first synthesized by RAFT/macromolecular design by the interchange of xanthates (RAFT/MADIX) polymerization of NVCL mediated by a chain transfer agent containing a hydroxyl function. The xanthate-end group was then removed from PNVCL by a radical-induced process. Finally, the hydroxyl end-capped PNVCL homopolymer was used as a macroinitiator in the ROP of ε-caprolactone (ε-CL) to obtain PNVCL-b-PCL block copolymers. These (co)polymers were characterized by Size Exclusion Chromatography (SEC), Fourier-Transform Infrared spectroscopy (FTIR), Proton Nuclear Magnetic Resonance spectroscopy (1H NMR), UV–vis and Differential Scanning Calorimetry (DSC) measurements. The critical micelle concentration (CMC) of the block copolymers in aqueous solution measured by the fluorescence probe technique decreased with increasing the length of the hydrophobic block. However, dynamic light scattering (DLS) demonstrated that the size of the micelles increased with increasing the proportion of hydrophobic segments. The morphology observed by cryo-TEM demonstrated that the micelles have a pointed-oval-shape. UV–vis and DLS analyses showed that these block copolymers have a temperature-responsive behavior with a lower critical solution temperature (LCST) that could be tuned by varying the block copolymer composition.

Modification of cellulose nanocrystal with dual temperature- and CO2-responsive block copolymers for ion adsorption applications

Cellulose nanocrystal (CNC)-grafted smart polymers have potential applications as adsorbents by providing simple regeneration process. In this study, carbon dioxide (CO2)- and temperature-responsive free block copolymers of N-isopropylacrylamide and (2-dimethylaminoethyl) methacrylate with different block lengths were synthesized using reversible addition-fragmentation chain transfer (RAFT) polymerization. In addition, CNC was modified with the similar block copolymers by surface-initiated RAFT method. The synthesized block copolymers were used in nitrate ion removal from aqueous solutions. The synthesis process was confirmed by Fourier-transform infrared spectroscopy, proton nuclear magnetic resonance (1H NMR) analysis, thermal gravimetric analysis, scanning electron microscopy, and transmission electron microscopy. Stimuli-responsivity of the free polymers was studied by pH measurement, turbidity investigation, and dynamic light scattering analysis. CO2-responsivity of the block copolymers in aqueous solution was confirmed by reduction of pH in the presence of CO2 by protonation of the PDMAEMA blocks. The copolymers with higher length of PDMAEMA showed highly intense CO2-responsivity. Deprotonation of the PDMAEMA units by purging N2 represents reversible responsivity of the copolymers. Turbidity analysis showed different critical solution temperatures (CST) for the block copolymers with various block lengths. Two different micellar and vesicular morphologies were observed for the self-assembled copolymers at temperatures above and below CST of the copolymers, which is related to the hydrophobic/hydrophilic block ratio. CO2-switched nitrate ion adsorption from aqueous solution at two temperatures (37 and 60 °C) was studied by UV–vis spectroscopy using the synthesized products as adsorbent. Adsorption of nitrate ions from aqueous solutions was increased by protonation of the PDMAEMA segments upon CO2 purging. Presence of CNC, morphology of the self-assembled copolymers, temperature, and time of CO2 purging affect the nitrite ion adsorption capacity. The maximum adsorption capacity (420 mg/g) is related to the sample with vesicular assemblies in aqueous solution and higher PDMAEMA block length at temperatures below CST of the block copolymer. N2 purging resulted in deprotonation of the PDMAEMA blocks and regeneration of the samples. Finally, the CNC substrate can be used in regeneration of the samples with simple filtration process in addition to the stimuli-regeneration process.

Synthesis and behaviour of PEG-b-PDEAm block copolymers in aqueous solution

Well-defined double hydrophilic block copolymers (DHBCs) of poly(ethylene glycol)-block-poly(N,N-diethylacrylamide) (PEG-b-PDEAm) were synthesized via a reversible addition-fragmentation chain-transfer (RAFT) polymerization of N,N-diethylacrylamide (DEAm) using dithioester terminated PEG of different chain lengths as macro-chain transfer agents. Controlled molecular weight and narrow molecular weight distribution were achieved as proven by size exclusion chromatography (SEC). Cloud points (CP) were determined via turbidity measurements with ultraviolet-visible spectroscopy (UV–vis) and LCST by differential scanning micro-calorimetry (micro-DSC). They range from 32 to 40 °C depending on the PDEAm length block and its concentration. Above the LCST, fluorescence spectroscopy and dynamic light scattering (DLS) demonstrated that the PEG-b-PDEAm copolymers self-organized into large aggregates. More interestingly, copolymers pre-aggregated at relatively high concentrations below the LCST.

Small molecule-mediated self-assembly behaviors of Pluronic block copolymers in aqueous solution: impact of hydrogen bonding on the morphological transition of Pluronic micelles.

The influence of hydrogen bonding on the self-assembly behaviors of Pluronic P123 micelles is experimentally and theoretically investigated by introducing three small molecules, i.e. propyl benzoate (PB), propyl paraben (PP) and propyl gallate (PG) into the aqueous solution. It is discovered that the number of phenolic hydroxyl groups and concentration of the tested small molecules exhibit a profound impact on the micellar morphology. Although all the small molecules increase the size and polydispersity of Pluronic micelles in a concentration-dependent manner, the micellar morphologies induced by them vary considerably as demonstrated by DLS and cryo-TEM measurement. PB, without phenolic hydroxyl, cannot bring about the morphological change of P123 micelles, while PP induces a series of morphological transitions from spheres to long worm-like micelles and then to unilamellar vesicles by increasing the PP content. Upon increasing the number of phenolic hydroxyls in small molecules, i.e. PG, the fusion of the intermicellar core takes place, resulting in the formation of large micelles and micellar clusters. A qualitative study by NMR reveals that the different locations of small molecules within the micelles are attributed to the balance of hydrogen bonding and hydrophobic interaction between small molecules and copolymers. In addition, molecular dynamics simulations (MDS) are performed to further confirm the experimental results and provide quantitative information on intermolecular interaction strength. It is supposed that the mechanism of micellar morphological transition mediated by small molecules is ascribed to the hydrogen bonding interactions with varying strengths between the PEO blocks and their phenolic hydroxyls, which governs their locations in micelles, affecting the free energies from different regions of micelles, and consequently leads to the varying micellar morphologies. This study deepens our understanding of the role of hydrgen bonding in the self-assembly behaviors of Pluronic micelles and provides an alternative strategy for manipulating the nanostructure of Pluronic micelles.

Self-assembly of stimuli-responsive block copolymers in aqueous solutions: an overview

The review reports an aqueous solution behavior of commercially available and easy-to-use polymers, i.e., Pluronics®- and PNIPAM-based block copolymers. Both the polymers are stimuli responsive in nature. The present review covers the different aspects of aggregation behavior of Pluronics®- and PNIPAM-based block copolymeric micelles. Here, a comparison of physical properties such as EO–PO block, CP, CMC and CMT is made. Such physical parameters can be modulated with ease by the presence of external stimuli, viz. electrolytes, organic additives such as alcohols, phenols, amides and acids, different types of surfactants and water-soluble polymers, and also by modification of end groups of Pluronics®. But in this review, our main focus is to study the addition of salts and non-electrolytes on the aggregation behavior of Pluronics®. With the help of above parameters, users can get idea about the stability, partition coefficient, solubilization capacity, etc. In analogy with Pluronics®, PNIPAM is also a thermo-responsive polymer with ~ 32 °C lower critical solution temperature (LCST). However, the LCST is independent of the degree of polymerization, i.e., molecular weight of homopolymer. However, the LCST can be tuned in the presence of external stimulus. PNIPAM-based di-block copolymers form various morphologies in different environments. An inverted morphology by double-hydrophilic-block copolymers is also possible. According to US and British Pharmacopoeia, some of the Pluronics® and PNIPAM are recognized as pharmaceutical excipients. Therefore, they have been extensively used for various pharmaceutical formulations. The other applications of these polymers are tissue engineering, bioseparation devices, active membranes, biosensors, rheological modifier, lithium batteries, etc.

Narrow molecular weight margins for the thermogelling property of polyester–polyether block copolymers in aqueous solutions

ABSTRACTPolyester–polyether block copolymers with thermogelling properties have been widely used in pharmaceutical and biomedical applications for their biocompatibility and degradation to nontoxic components. The biodegradable polymers, such as poly(lactide‐co‐glycolide) and poly(lactide‐co‐caprolactone) (PLCL), have been used as the polyester block. The most commonly used polyether has been poly(ethylene glycol) (PEG). The thermogelling polymers dissolve in cold water, but become a semisolid gel at higher temperatures, for example, body temperature. This thermogelling property, however, occurs only within very narrow molecular weight ranges of the polyester at given polyether blocks. Only a few hundred Dalton differences in the polyester block can turn a thermogelling polymer into a water‐insoluble polymer. This study describes the hydrophilic and hydrophobic block sizes for endowing the thermogelling property and a simple, water‐free, synthesis of new thermogelling PLCL–PEG–PLCL triblock polymers. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 48673.

The preparation and property of photo- and thermo-responsive hydrogels with a blending system

Hydrogels are the attractive biomaterials for biomedical applications. The dual-stimuli-responsive system, which is sensitive to both temperature and UV irradiation, was achieved through the self-assembly of amphiphilic block copolymers in aqueous solution and the cleavage of ο-nitrobenzyl (NB) ester groups under UV irradiation. The copolymer of poly(e-caprolactone)-b-ο-nitrobenzyl-poly(ethylene glycol)-ο-nitrobenzyl-b-poly(e-caprolactone) (PCL-NB-PEG-NB-PCL) was prepared by ring-opening polymerization (ROP) and nucleophilic substitution reaction of e-caprolactone (e-CL) using photo-sensitized polyethylene glycol as an initiator. After blending with poly(e-caprolactone)-b-poly(ethylene glycol)-b-poly(e-caprolactone) (PCL-PEG-PCL), the system exhibited the promising dual sensitivity with wide gel-phase window and controllable sensitive properties. The structures and dual-responsive behaviors were characterized by 1H-NMR, GPC, DMA, UV–Vis, DLS and SEM. The results demonstrated the temperature and photo-sensitivity of the synthesized hydrogel and indicated that the blending of these two copolymers can easily adjust the phase transition temperature and broaden the gel-phase window through the content of NB groups in PCL-NB-PEG-NB-PCL and the hydrophilic/hydrophobic balance of system.

Tannic Acid-Mediated Aggregate Stabilization of Poly(N-vinylpyrrolidone)-b-poly(oligo (ethylene glycol) methyl ether methacrylate) Double Hydrophilic Block Copolymers.

The self-assembly of block copolymers in aqueous solution is an important field in modern polymer science that has been extended to double hydrophilic block copolymers (DHBC) in recent years. In here, a significant improvement of the self-assembly process of DHBC in aqueous solution by utilizing a linear-brush macromolecular architecture is presented. The improved self-assembly behavior of poly(N-vinylpyrrolidone)-b-poly(oligo(ethylene glycol) methyl ether methacrylate) (PVP-b-P(OEGMA)) and its concentration dependency is investigated via dynamic light scattering (DLS) (apparent hydrodynamic radii ≈ 100–120 nm). Moreover, the DHBC assemblies can be non-covalently crosslinked with tannic acid via hydrogen bonding, which leads to the formation of small aggregates as well (apparent hydrodynamic radius ≈ 15 nm). Non-covalent crosslinking improves the self-assembly and stabilizes the aggregates upon dilution, reducing the concentration dependency of aggregate self-assembly. Additionally, the non-covalent aggregates can be disassembled in basic media. The presence of aggregates was studied via cryogenic scanning electron microscopy (cryo-SEM) and DLS before and after non-covalent crosslinking. Furthermore, analytical ultracentrifugation of the formed aggregate structures was performed, clearly showing the existence of polymer assemblies, particularly after non-covalent crosslinking. In summary, we report on the completely hydrophilic self-assembled structures in solution formed from fully biocompatible building entities in water.