Triblock Copolymer Research Articles

Co-assembly of Amphiphilic Triblock Copolymers with Nanodrugs and Drug Release Kinetics in Solution.

Polymeric vesicles present great potential in disease treatment as they can be featured as a structurally stable and easily functionalized drug carrier that can simultaneously encapsulate multiple drugs and release them on-demand. Based on the dissipative particle dynamics (DPD) simulation, the drug-loaded vesicles were designed by the co-assembly process of linear amphiphilic triblock copolymers and hydrophobic nanodrugs in solvents, and most importantly, the drug release behavior of drug-loaded vesicles were intensively investigated. The drug-loaded aggregates, such as vesicles, spherical micelles, and disk-like micelles, were observed by varying the size and concentration of nanodrugs and the length of the hydrophobic block. The distribution of nanodrugs in the vesicles was intensively analyzed. As the size of the nanodrugs increases, the localization of nanodrugs change from being unable to fully wrap in the vesicle wall to the uniform distribution and finally to the aggregation in the vesicles at the fixed concentration of nanodrugs. The membrane thickness of the drug-loaded polymeric vesicle can be increased, and the nanodrugs localized closer to the center of the vesicle by increasing the length of the hydrophobic block. The nanodrugs will be released from vesicles by varying the interactions between the nanodrug and the solvent or the hydrophobic block and the solvent, respectively. We found that the release kinetics conforms to the first-order kinetic model, which can be used to fit the cumulative release rate of nanodrugs over time. The results showed that increasing the size of nanodrugs, the length of hydrophobic block, and the interaction parameters between the hydrophobic block and the solvent will slow down the release rate of the nanodrug and change the drug release process from monophasic to biphasic release model.

Efficient green Cr(VI) adsorbent from sorghum waste: Eco-designed functionalized mesoporous silica FDU-12

This paper presents an eco-design approach to the synthesis of a highly efficient Cr(VI) adsorbent, utilizing a positively charged surface mesoporous FDU-12 material (designated as MI-Cl-FDU-12) for the first time. The MI-Cl-FDU-12 anion-exchange adsorbent was synthesized via a facile one-pot synthesis approach using sodium silicate extracted from sorghum waste as a green silica source, 1-methyl-3-(triethoxysilylpropyl) imidazolium chloride as a functionalization agent, triblock copolymer F127 as a templating or pore-directing agent, trimethyl benzene as a swelling agent, KCl as an additive, and water as a solvent. The synthesis method offers a sustainable and environmentally friendly approach to the production of a so-called “green” adsorbent with a bimodal micro-/mesoporous structure and a high surface area comparable with the previous reports regarding FDU-12 synthesis. MI-Cl-FDU-12 was applied as an anion exchanger for the adsorption of toxic Cr(VI) oxyanions from aqueous media and various kinetic and isotherm models were fitted to experimental data to propose the adsorption behavior of Cr(VI) on the adsorbent. Langmuir model revealed the best fit to the experimental data at four different temperatures, indicating a homogeneous surface site affinity. The theoretical maximum adsorption capacities of the adsorbent were found to be 363.5, 385.5, 409.0, and 416.9 mg g−1 at 298, 303, 308, and 313 K, respectively; at optimal conditions (pH=2, adsorbent dose=3.0 mg, and contact time of 30 min), surpassing that of most previously reported Cr(VI) adsorbents in the literature. A regeneration study revealed that this adsorbent possesses outstanding performance even after six consecutive recycling.

Morphology and confinement effects on crystallization kinetics in polyethylene containing block copolymers

This paper investigates the morphology and crystallization kinetics of polyethylene (PE) containing block copolymers, differing in block number (di- vs. triblock copolymers) and composition (ABA triblock co- vs. ABC triblock terpolymers). In these block copolymers, the crystallizable PE block is linked to amorphous poly(methyl methacrylate) (PMMA) and/or polystyrene (PS) blocks, and for one triblock terpolymer, poly(ethylene oxide) (PEO) was introduced as an additional crystallizable block. The topological confinement exerted by the covalent linkage of PE to the other blocks (glassy PMMA and PS, PEO) in combination with the morphological confinement into different PE microdomains (cylinders, lamella) significantly influence the crystallization behavior, resulting in slower crystallization kinetics compared to pure PE. The strongest effects were observed for triblock terpolymers, where the lamellar PE domains are disrupted by PS cylinders or distorted PS domains. This research enhances our understanding of block copolymers with confined crystallizable segments, aiding in tailored material design.

Reversing Sunitinib Resistance Facilitated by ITGA1 Through the PI3K/Akt/Bcl-2 Pathway Using Nano Co-Delivery System in Renal Cell Carcinoma

For genitourinary cancers, renal cell carcinoma (RCC) is the third leading cause of death, while target drug resistance has always been a difficult problem. Integrin alpha 1 (ITGA1) is a member of the integrin family, which is significant for the pathogenesis, development, and drug resistance of various malignant tumors. However, it remains unclear for the ITGA1 functions in renal cell carcinoma sunitinib resistance. In this study, we found that the ITGA1 gene facilitates renal cell carcinoma sunitinib resistance through the PI3K/Akt/Bcl-2 signaling pathway. Based on this, we developed a co-delivery system designated as Su/Si-PEAL NPs for the synergistic delivery of ITGA1 small interfering RNA (siRNA) and sunitinib using monomethoxy polyethylene glycol-polylactic acid/glycolic acid-poly-L-lysine triblock copolymer (mPEG-PLGA-PLL, PEAL) as the backbone material. Furthermore, the results of a series of functional experiments confirmed that this codelivery system was capable of downregulating the expression of ITGA1 and enhancing the sensitivity of 786-O-R cells to sunitinib. This co-delivery system could be an efficient approach for reversing sunitinib resistance in renal cell carcinoma.

Ionic Strength Effect in the Equilibrium and Rheological Behavior of an Amphiphilic Triblock Copolymer at the Air/Solution Interface

This study investigates the effect of an inert salt (NaCl) on the equilibrium interfacial tension and dilatational modulus of Pluronic F-68 copolymer, a triblock copolymer consisting of two terminal blocks of poly(ethylene oxide) and a less hydrophilic central block of poly(propylene oxide). Interfacial tension measurements were carried out using a surface force balance and a drop shape tensiometer, while rheological measurements were carried out in two different frequency ranges. This involved the use of the oscillatory barrier/droplet method and electrocapillary wave measurements, complemented by an appropriate theoretical framework. This work aimed to elucidate the influence of NaCl on the interfacial behavior of Gibbs monolayers of Pluronic F-68. In addition, this study highlights some of the technical and theoretical limitations associated with obtaining reliable dilatational rheological data at high frequencies (<1 kHz) using electrocapillary wave measurements. The results provide valuable insights into the interplay between salt presence and interfacial properties of Pluronic F-68 and highlight the challenges of obtaining accurate dilatational rheological data under specific measurement conditions.

A mathematical model of thermoplastic elastomers for analysing the topology of microstructures and mechanical properties during elongation

In this study, a mathematical model based on graph theory is developed to analyse the deformed structures and mechanical properties of thermoplastic elastomers (TPEs) using ABA-type triblock copolymers. TPEs exhibit a network structure formed by bridge chains; deformation of this network structure causes stress. During the deformation of TPEs, domain breakage and coalescence occur, accompanied by topological changes in the chains, such as conformational transitions between the bridge and loop chains. By employing the mathematical concepts of harmonic realization of graphs in the physical space and the tension tensor to quantify the stress in the bridge-chain network structure, an effective method for analysing topologicalchanges in microstructures caused by elongation is proposed. As an application of this method, optimal geometric structures of block copolymers with desired functionalities can be determined.

Thiol‐ene click chemistry for constructing transition layer to enhance the interface interaction between polyacrylonitrile fiber and styrene‐butadiene‐styrene modified asphalt

AbstractBased on the high chemical stability and excellent end‐group functionalization capability of polyhedral oligomeric silsesquioxane (POSS), this study utilized thiol‐functionalized POSS (POSS‐SH) in a click chemistry reaction with styrene‐butadiene‐styrene triblock copolymer (SBS). The objective was to design a functional group forming a chemical bond with the polymer matrix, resulting in the preparation of thiol‐functionalized polyacrylonitrile (PAN) fibers chemically cross‐linked with POSS‐SH/PAN/SBS hybrid material. This hybrid material not only enhanced the compatibility between the components but also facilitated a connection between the fiber and SBS, thereby improving the mechanical properties of the modified asphalt. Fourier transform infrared spectroscopy, field emission scanning electron microscopy (FESEM), and atomic force microscopy analyses confirmed the successful modification of POSS‐SH/PAN fibers. FESEM analysis of the modified asphalt verified that POSS‐SH/PAN fibers contributed to strengthening the interfacial performance between the fiber and asphalt. Cone penetration and dynamic shear rheometer tests indicated that, compared to SBS‐modified asphalt, PAN/SBS and POSS‐SH/PAN/SBS‐modified asphalt exhibited enhanced shear strength, deformation resistance, and viscoelastic properties. Additionally, at 46°C, the storage modulus (G′) of 1.5% POSS‐SH/PAN/SBS‐modified asphalt increased by 11% compared to 1.5% PAN/SBS asphalt, with increases of 13.75% and 10.8% in loss modulus (G″) and complex modulus (G*), respectively.

Polymer-Drug Conjugates Codeliver a Temozolomide Intermediate and Nitric Oxide for Enhanced Chemotherapy against Glioblastoma Multiforme.

Polymer-drug conjugates (PDCs) provide possibilities for the development of multiresponsive drug delivery and release platforms utilized in cancer therapy. The delivery of Temozolomide (TMZ, a DNA methylation agent) by PDCs has been developed to improve TMZ stability under physiological conditions for the treatment of glioblastoma multiforme (GBM); however, with inefficient chemotherapeutic efficacy. In this work, we synthesized an amphiphilic triblock copolymer (P1-SNO) with four pendant functionalities, including (1) a TMZ intermediate (named MTIC) as a prodrug moiety, (2) a disulfide bond as a redox-responsive trigger to cage MTIC, (3) S-nitrosothiol as a light/heat-responsive donor of nitric oxide (NO), and (4) a poly(ethylene glycol) chain to enable self-assembly in aqueous media. P1-SNO was demonstrated to liberate MTIC in the presence of reduced glutathione and release gaseous NO upon exposure to light or heat. The in vitro results revealed a synergistic effect of released MTIC and NO on both TMZ-sensitive and TMZ-resistant GBM cells. The environment-responsive PDC system for codelivery of MTIC and NO is promising to overcome the efficacy issue in TMZ-based cancer therapy.

Investigating the stability of vitamin D3 and Bifidobacterium lactis nanoparticles coated with polycaprolactone-polyethylene glycol-polycaprolactone triblock copolymer in Iranian white cheese and determining its physicochemical and sensory properties

ObjectiveTo investigate the stability and efficacy of vitamin D3 and Bifidobacterium lactis nanoparticles coated with polycaprolactone-polyethylene glycol-polycaprolactone (PCL-PEG-PCL) in enhancing the nutritional value of Iranian white cheese and to assess their impact on the cheese's physicochemical and sensory properties. MethodsBifidobacterium lactis and vitamin D3 were encapsulated using PCL-PEG-PCL. The particle size was analyzed using Dynamic Light Scattering (DLS). Five different cheese groups were produced and analyzed over two months. This included assessing microbial viability in simulated gastric and intestinal environments, quantifying vitamin D3 content, and evaluating physicochemical and sensory characteristics using a 9-point hedonic scale. ResultsThe Cheese with Bifidobacterium lactis coated with PCL-PEG-PCL and vitamin D3 nanoparticles (BCND3), showed a marked improvement in the stability of both Bifidobacterium lactis and vitamin D3. Specifically, the coated bacteria maintained a concentration of 106 cfu/g until day 45 in the intestinal model, demonstrating effective protection against the acidic gastric environment. The vitamin D3 nanoparticles displayed enhanced stability within the cheese matrix, contributing to the nutritional value and potentially extending the shelf life. Physicochemically, initial pH reduction due to lactic acid production stabilized by day 60, aligning with other groups. Sensory evaluation revealed a preference for the softer texture of cheese with vitamin D3 nanoparticles, suggesting a positive impact on consumer acceptability. ConclusionThe application of PCL-PEG-PCL coating significantly improved the stability of probiotics and vitamin D3 in cheese. This method proved effective in protecting Bifidobacterium lactis from harsh gastrointestinal conditions and in sustaining vitamin D3 content, with a notable impact on the cheese's sensory qualities. These findings highlight the potential of this coating technique in food fortification strategies.

Controlling the function of bioactive worm micelles by enzyme-cleavable non-covalent inter-assembly cross-linking

Drugs that form self-assembled supramolecular structures to be most-active is a promising way of creating new highly specific and active pharmaceuticals. Controlling the activity of bioactive supramolecular structures such as drug-loaded micelles is possible by both core/shell and inter-assembly cross-linking. However, if the flexibility of the assembly is mandatory for the activity cross-linking is not feasible. Thus, such structures cannot be manipulated in their activity.The present study demonstrates a novel concept to control the activity of not drug-releasing, non-cross-linked bioactive superstructures. This is achieved by formation of nanostructured nanoparticles derived by non-covalent inter-assembly cross-linking of the superstructures. This is shown on the example of amphiphilic diblock-copolymers conjugated with the antibiotic ciprofloxacin (CIP). These polymer-antibiotic conjugates form worm micelles, which greatly activate the conjugated antibiotic without releasing it. Non-covalent inter-assembly cross-linking of these CIP-worm-micelles with amphiphilic triblock copolymers terminated with lipase-cleavable esters leads to nanostructured nanoparticles that resemble cross-linked worm micelles and show an up to 135-fold lower activity than the free worm micelles. The activity of the worm-micelles can be fully recovered by cleaving the end groups of the polymeric cross-linker with lipase.

The effects of additive agents on zinc and zinc–nickel alloys electrodeposited on steel substrates in acidic electrolytes

The influence of glycine, as a chelating agent, and triblock copolymer mixture of PPG-PEG-PPG and PEG1000, as a suppressor agent, on the deposition mechanisms of zinc and zinc-nickel alloys were studied by cyclic voltammetry (CV) and potentiometric electrochemical impedance spectroscopy (PEIS), using electrolyte solutions of chlorinated acid. Cyclic voltammetry measurements show that the composition of the electrolytic solution affects the voltammogram profiles. Complementary PEIS investigations allowed the electrodeposition mechanisms to be highlighted depending on the composition of the electrolytic solution. The electrodeposition of zinc, in the absence of additives, occurs in a single cathodic wave from the ZnCl3− species, whereas in the presence of glycine, a second more cathodic reduction wave is relative to the Zn(Gly)22+ species. The presence of the PPG-PEG-PPG and PEG1000 triblock copolymer induces a clear inhibition of the zinc reduction. Nevertheless, the zinc electrodeposition follows a three-dimensional instantaneous nucleation. The zinc electroplating mechanism involves a capacitive semi-circle at high frequency and two inductive loops at medium and low frequencies assigned to two adsorbed intermediates onto the substrate whatever the electrolyte composition. The presence of the polymer mixture affects the zinc reduction by increasing the charge-transfer resistance and the adsorption phenomena on the substrate. The electrodeposition of zinc-nickel alloys reveals a single reduction wave, from ZnCl3− and Ni(Gly)2+ species, and multiple anodic signals depending on the electrolytic composition, according to the presence of glycine to chelate the nickel species. The zinc-nickel electroplating was evidenced to be a multiple-step process with a three-dimensional instantaneous nucleation, including intermediate species adsorbed onto the substrate. The equivalent circuit proposed consists of two capacitive half-circles separated by an inductive loop for any electrolytic solution. However, the impedance spectra were affected by the presence of glycine by modifying the inductive loop reflecting the first adsorbed intermediate (Ni(I)ads). The morphology of zinc and zinc-nickel, with a nickel content between 14 and 19 wt%, is affected by the electrolyte composition, however with the same crystal lattice. The preferential orientation of the lattice was shown to depend on the additives present in the solution.

An Adaptable Drug Delivery System Facilitates Peripheral Nerve Repair by Remodeling the Microenvironment.

The multifaceted process of nerve regeneration following damage remains a significant clinical issue, due to the lack of a favorable regenerative microenvironment and insufficient endogenous biochemical signaling. However, the current nerve grafts have limitations in functionality, as they require a greater capacity to effectively regulate the intricate microenvironment associated with nerve regeneration. In this regard, we proposed the construction of a functional artificial scaffold based on a "two-pronged" approach. The whole system was developed by encapsulating Tazarotene within nanomicelles formed through self-assembly of reactive oxygen species (ROS)-responsive amphiphilic triblock copolymer, all of which were further loaded into a thermosensitive injectable hydrogel. Notably, the hydrogel exhibits obvious temperature sensitivity at a concentration of 6 wt %, and the nanoparticles possess concentration-dependent H2O2-response capability with a controlled release profile in 48 h. The combined strategy promoted the repair of injured peripheral nerves, attributed to the dual role of the materials, which mainly involved providing structural support, modulating the immune microenvironment, and enhancing angiogenesis. Overall, this study opens up intriguing prospects in tissue engineering.

Influence of volume expansion in NaCl crystallization on the physical properties and molecular structure of asphalt: A MD simulation study

The pavement damage caused by salt-induced volume expansion is becoming increasingly noticeable. Molecular dynamics (MD) method was applied to evaluate the effects of varied volumes of NaCl crystals on physical properties and structure of asphalt. The effects of NaCl crystals on the compatibility between styrene–butadiene–styrene triblock copolymer (SBS) and asphalt, as well as the influence of SBS on the diffusion coefficient of NaCl crystals in the asphalt system, were investigated alongside their effects on the physical modulus and molecular structure of asphalt. The results show that the solubility parameter of the asphalt blends decreases as the volume of NaCl crystals increases. Specifically, the solubility parameter decreases by 52.5 % for the biaxial crystalline growth of NaCl and asphalt blends compared to the matrix asphalt. The analysis of the ion diffusion coefficient reveals that the primary disruption of NaCl crystals in asphalt blends is due to early Cl- and late Na+ diffusion. Furthermore, the rise in shear modulus of the asphalt blends suggests that the salt erosion process of SBS-modified asphalt is advantageous for its high temperature and shear resistance. The changes in peak radial distribution function and radius of gyration indicate that the inclusion of NaCl and SBS into asphalt is a physical aging process. In this case, SBS incorporation acts as a reinforcement to the asphalt to retard the erosion of NaCl.

Thermo-sensitive PLGA-PEG-PLGA hydrogel for sustained release of EGF to inhibit cervical cancer recurrence

Overexpression of epidermal growth factor receptor (EGFR) in cancer is a key cause of recurrence of cervical cancer (CC). Although the EGF-EGFR pathway has been studied for decades, preventing tumor growth and recurrence caused by peripheral EGF remains a great challenge. In this work, a strategy is proposed to reduce the stimulation of high concentration EGF on tumor growth by using a thermo-sensitive hydrogel. The hydrogel is a triblock copolymer composed of polyethylene glycol (PEG) and poly (lactide glycolide) (PLGA). Based on the excellent temperature sensitivity, carrier capacity, swelling property and biocompatibility, the hydrogel can absorb the liquid around the tumor by injection and release EGF continuously at low concentration. The inhibitory effect of hydrogel on tumor growth is fully confirmed by an implanted tumor mouse model with human cervical cancer cell lines (HeLa) using triple-immunodeficient NCG mice. Compared with free EGF, the EGF-loaded hydrogel can hardly induce surface plasmon resonance (SPR) response, which proves that hydrogel can effectively weaken cytoskeleton rearrangement and inhibit cell migration by continuously releasing low concentration EGF. In addition, the EGF-loaded hydrogel can reduce cell proliferation by delaying the progress of cell cycle progression. Taken together, the hydrogel can effectively protect tumor microenvironment from the stimulation of high concentration EGF, delay cancer cellular processes and tumor growth, and thus providing an approach for inhibiting tumor recurrence of CC.

Amphiphilic pH-responsive ABC triblock copolymers via RAFT-mediated aqueous PISA and comparison with their A-b-(B-co-C) diblock copolymer counterparts

The influence of the macroRAFT agent architecture on the morphology of the self-assemblies obtained by aqueous RAFT dispersion polymerization in PISA is studied by comparing amphiphilic AC, A(B-co-C) diblocks and ABC triblock copolymers, constituted of N,N-dimethylacrylamide (DMAm = A), acrylic acid (AA = B) and N-cyanomethylacrylamide (CMAm = C) monomer units. The aim of this study is to better understand the impact of the presence of pH-sensitive acrylic acid units and their spatial distribution in block copolymers. Generally, the presence of a fully protonated intermediate block of PAA between the two blocks (based on PDMAm and PCMAm) favors the formation of higher-order morphologies. These ABC triblock copolymers assemblies are pH-responsive and can undergo morphological transitions through the controlled deprotonation or protonation of the PAA segment, but do not completely dissociate at high pH (i.e. when AA units are fully ionized) unlike their A(B-co-C) diblock counterparts, where the pH-responsive monomer unit is homogeneously distributed within the solvophobic block.

Synthesis of Polyesters Containing Long Aliphatic Methylene Units by ADMET Polymerization and Synthesis of ABA-Triblock Copolymers by One-Pot End Modification and Subsequent Living Ring-Opening Polymerization.

The synthesis of high-molecular-weight (Mn up to 62,000 g/mol) polyesters has been achieved by acyclic diene metathesis (ADMET) polymerization of α,ω-dienes prepared from biobased bis(undec-10-enoate) and diols [ethylene glycol (M1), propylene glycol (M2), 1,9-nonanediol (M3), 1,4-benzenedimethanol (M4), and hydroquinone (M5)] using ruthenium-carbene catalysts. Replacement of the solvent during the ADMET polymerization was effective for obtainment of the high-molecular-weight polymers (expressed as P1-P5). The melting temperatures (Tm) in the resultant polyesters were dependent upon the diol (middle) segment employed, and the polymer prepared from M5 exceeded 100 °C (a Tm value of 122.5 °C). The polymerization of M3 and M4 in the presence of 1,4-cis-diacetoxy-2-butene (DAB, as the chain transfer agent) afforded the telechelic polyesters [P3(OAc)2 and P4(OAc)2, respectively] containing acetoxy end groups exclusively. The resultant polymers containing hydroxy group termini [P3(OH)2 and P4(OH)2], prepared by the selective deprotection of the acetoxy end groups, were treated with AlEt3 followed by addition of ε-caprolactone to afford the ABA-type triblock copolymers exclusively, through a living ring-opening polymerization. The depolymerization (hydrolysis) under basic conditions (NaOH aqueous solution) of P3 was explored.

Micelles regulated thin film nanocomposite membrane with enhanced nanofiltration performance

The desalination performance of thin film nanocomposite (TFN) membranes is significantly influenced by the nature of nanofillers and the structure of the polyamide (PA) layer. Herein, a micelles regulated interfacial polymerization (MRIP) strategy is reported for the preparation of TFN membranes with enhanced nanofiltration (NF) performance. Specially, stable and ultrafine micelles, synthesized from the poly(ethylene oxide)-b-poly(4-vinyl pyridine)-b-polystyrene (PEO-PVP-PS) triblock copolymers, were utilized as regulators in the aqueous phase during the interfacial polymerization (IP) process. TFN membranes were fabricated with varying concentrations of micelles to improve their properties and performances. The structure of the PA layer was further regulated by modulating the content of trimesoyl chloride (TMC), which significantly enhances the performance of the TFN membrane with micelles. Attributable to the homogeneously dispersed micelles and the modified PA layer, the optimized membrane denoted as TFN-2–0.3 exhibits an improved separation performance of 20.7 L m-2h−1 bar−1 and 99.3 % Na2SO4 rejection, demonstrating nearly twice the permeance and 2.7 % higher rejection than that of the original control membrane, respectively. The mechanism of this MRIP strategy was investigated through the diffusion experiments of piperazine (PIP) and interfacial tension tests. The incorporated micelles effectively lower the interfacial tension, promote the diffusion of PIP and accelerate the IP reaction, resulting in a denser and thinner PA layer. Collectively, these findings demonstrate that TFN membranes with micelles exhibit increased roughness, enhanced hydrophilicity, superior rejection to divalent salts, and better acid-base resistance, highlighting their potential applications in the design of TFN membranes.

Adsorption of triblock copolymers confined between two plates: An analytical approach.

We present an approximate analytical approach to the adsorption problem of ABA triblock copolymers confined between two parallel plates in a θ solvent and give the expression of the propagator q(x, t) as a piece-wise function by solving the modified diffusion equation. In this way, the role of separation between the two plates, adsorption energy and block lengths on segment concentration profile, chain conformations, and interaction potential is then investigated, which agrees well with the numerical results. It is demonstrated that there are parallels between lengthening adsorbing A blocks and increasing surface affinity: strong adsorption and long adsorbing blocks favor the formation of loops and bridges, whereas more tails and free chains exist in the case of weak adsorption and short A blocks at large separations. For moderate and strong adsorptions, the bridging fraction begins to plummet at a separation larger than the end-to-end distance of non-adsorbing B block RB and becomes negligible at above 2RB owing to the entropy effect. The depth of the potential well in the interaction potential profile depends on the adsorption energy and A block length, while the location of the potential minimum corresponds to the onset of the sharp decrease in bridges.

Tailoring pore size of mesoporous silica and organosilica using biodegradable pentablock copolymer templates via EISA process

In this work, we have designed unique poly(lactic acid-co-glycolic acid)-b-poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide)-b-poly(lactic acid-co-glycolic acid) pentablock copolymers using Pluronic F68 and F108 triblock copolymers as macroinitiators. The poly(lactic acid-co-glycolic acid) (PLGA) blocks were attached as glycolide and lactide monomers at the both ends of each F68 and F108 triblock copolymer. The molecular weights and the block fractions were confirmed by gel permeation chromatography (GPC) and proton nuclear magnetic resonance (1H NMR) for the four kinds of pentablock copolymers. Using these pentablock copolymers as templates, we synthesized mesoporous ethane-silicas as well as silicas by the evaporation-induced self-assembly (EISA) method. 1,2-bis(triethoxysily)ethane (BTEE) were used as an organosilica precursor. The mesoporous ethane-silica samples were characterized using synchrotron small angle X-ray scattering (SAXS), nitrogen sorption experiments, transmission electron microscopy (TEM), and solid-state 29Si CP-MAS NMR. Based on the experimental results, it was confirmed that the porosity and pore diameter can be varied with the PLGA weight fraction of the pentablock copolymer. It is due to the PLGA block in polymer forming the hydrophobic domain in micelles, which leads to the formation of increased pore size over 20 nm without any additive pore expander. In addition, it seems that as the organosilica precursor increases, the association number of block copolymers forming one micelle decreases, resulting in a decrease in pore size. In summary, the polymer template plays a vital part in tuning the structure of the mesoporous ethane-silica samples. Thus, the development of synthetic method of mesoporous organosilica materials using polymer templates with different topology is still challenging and can endow the unique structure and property for mesoporous organosilica for future applications.

Gelation upon the Mixing of Amphiphilic Graft and Triblock Copolymers Containing Enantiomeric Polylactide Segments through Stereocomplex Formation.

Biodegradable injectable polymer (IP) systems that form hydrogels in situ when injected into the body have considerable potential as medical materials. In this paper, we report a new two-solution mixed biodegradable IP system that utilizes the stereocomplex (SC) formation of poly(l-lactide) (PLLA) and poly(d-lactide) (PDLA). We synthesized triblock copolymers of PLLA and poly(ethylene glycol), PLLA-b-PEG-b-PLLA (tri-L), and a graft copolymer of dextran (Dex) attached to a PDLA-b-PEG diblock copolymer, Dex-g-(PDLA-b-PEG) (gb-D). We found that a hydrogel can be obtained by mixing gb-D solution and tri-L solution via SC formation. Although it is already known that graft copolymers attached to enantiomeric PLLA and PDLA chains can form an SC hydrogel upon mixing, we revealed that hydrogels can also be formed by a combination of graft and triblock copolymers. In this system (graft vs. triblock), the gelation time was shorter, within 1 min, and the physical strength of the resulting hydrogel (G' > 100 Pa) was higher than when graft copolymers were mixed. Triblock copolymers form micelles (16 nm in diameter) in aqueous solutions and hydrophobic drugs can be easily encapsulated in micelles. In contrast, graft copolymers have the advantage that their molecular weight can be set high, contributing to improved mechanical strength of the obtained hydrogel. Various biologically active polymers can be used as the main chains of graft copolymers, and chemical modification using the remaining functional side chain groups is also easy. Therefore, the developed mixing system with a graft vs. triblock combination can be applied to medical materials as a highly convenient, physically cross-linked IP system.