Controlled self-assembly into diverse stimuli-responsive microstructures: from microspheres to branched cylindrical micelles and vesicles

A series of amphiphilic PDMAEMA–SS–PCL chains with variable ratios of hydrophilic poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) to hydrophobic poly(ε-caprolactone) (PCL) were prepared via ring-opening polymerization, in which the two different moieties were linked via a disulfide bond with reduction responsiveness. After cross-linking by the photodegradable o-nitrobenzyl linkage, the amphiphilic chains could self-assemble into microspheres, branched cylindrical micelles and vesicles, which were responsive to the reduction agent dl-dithiothreitol and UV light irradiation through different mechanisms.

A series of cross-linked amphiphilic PDMAEMA–SS–PCL were prepared, which could self-assemble into diverse microstructures with reduction and light responsiveness.     

Optical stretching of giant unilamellar vesicles with an integrated dual-beam optical trap

We have integrated a dual-beam optical trap into a microfluidic platform and used it to study membrane mechanics in giant unilamellar vesicles (GUVs). We demonstrate the trapping and stretching of GUVs and characterize the membrane response to a step stress. We then measure area strain as a function of applied stress to extract the bending modulus of the lipid bilayer in the low-tension regime.OCIS codes: (000.1430) Biology and medicine, (350.4855) Optical tweezers or optical manipulation     

Fabrication and characterization of structurally stable pH-responsive polymeric vesicles by polymerization-induced self-assembly

Smart polymeric vesicles with both tertiary amine and epoxy functional groups were fabricated for the first time via a reversible addition–fragmentation chain transfer dispersion polymerization approach, using (2-(diisopropylamino)ethyl methacrylate (DIPEMA) and glycidyl methacrylate (GlyMA) in an ethanol–water mixture. Monitoring of the in situ polymerization revealed the low molecular weight distributions and the intermediate structures of spheres and worms, indicating an evolution in particle morphology. A phase diagram was constructed for reproducible fabrication of the vesicles, and copolymer composition was found to be more related to particle morphology. The vesicles exhibited superior structural stability for the cross-linking of the core through epoxydiamine chemistry, and intelligent pH responsibility due to the presence of the tertiary amine groups. The cross-linked vesicles showed good stability and reversibility during the swelling and shrinking cycles by switching the pH values, which endowed them with potential cell-like transmission functions. This research thus provides a method for producing structurally stable pH-responsive polymeric vesicles, and the reported vesicles are based on commercially available starting materials for possible industrial scale-up.

Smart polymeric vesicles with both tertiary amine and epoxy functional groups were fabricated for the first time via a reversible addition–fragmentation chain transfer dispersion polymerization approach.     

Translocation of silica nanospheres through giant unilamellar vesicles (GUVs) induced by a high frequency electromagnetic field

Membrane model systems capable of mimicking live cell membranes were used for the first time in studying the effects arising from electromagnetic fields (EMFs) of 18 GHz where membrane permeability was observed following exposure. A present lack of understanding of the mechanisms that drive such a rapid change in membrane permeabilization as well as any structural or dynamic changes imparted on biomolecules affected by high-frequency electromagnetic irradiation limits the use of 18 GHz EMFs in biomedical applications. A phospholipid, 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) labelled with a fluorescent marker 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine-N-(lissamine rhodamine B sulfonyl) (rhodamine-DOPE) was used in constructing the giant unilamellar vesicles (GUVs). After three cycles of exposure, enhanced membrane permeability was observed by the internalisation of hydrophilic silica nanospheres of 23.5 nm and their clusters. All-atom molecular dynamics simulations of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) membranes exposed to high frequency electric fields of different field strengths showed that within the simulation timeframe only extremely high strength fields were able to cause an increase in the interfacial water dynamics characterized by water dipole realignments. However, a lower strength, high frequency EMF induced changes of the water hydrogen bond network, which may contribute to the mechanisms that facilitate membrane permeabilization in a longer timeframe.

Membrane model systems capable of mimicking live cell membranes were used for the first time in studying the effects arising from electromagnetic fields (EMFs) of 18 GHz where membrane permeability was observed following exposure.     

An experimental and theoretical investigation into the self-assembly of a chemically modified high-χ coil–rod diblock copolymer

A precursor diblock copolymer with a silicon backbone, polystyrene-block-poly(methylvinylsiloxane), was synthesized, and 1H,1H,2H,2H-perfluorodecanethiol was quantitatively introduced into the backbone via a thiol-ene reaction to yield a novel coil–rod diblock copolymer, poly(styrene-block-poly(2-((3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-heptadecafluorodecyl)thio)ethyl)methylsiloxane). The ultra-hydrophobicity of the introduced perfluoroalkyl side chain enhanced the segregation between counter-blocks and significantly increased the χ value, which is essential for minimizing the size of self-assembled domains for lithographic applications. Thus, self-assembled domains with a minimal spacing of approximately 10 nm were formed. A hexagonally packed array with significant anisotropy was observed in the self-assembled morphology by small-angle X-ray scattering and transmission electron microscopy. Such an array was precisely reproduced by modified self-consistent field theory (SCFT) calculation developed for the coil–rod structure. Furthermore, the phase diagram was estimated, and the morphological dependence on the relative scale of the rod unit was investigated by SCFT prediction.

A high-χ coil-rod diblock copolymer capable of forming unique anisotropic hexagonally packed cylindrical domains evidenced by experimental and theoretical study.     

Emu model of full-range femoral head osteonecrosis induced focally by an alternating freezing and heating insult

The emu, a large bipedal bird with hip joint biomechanics similar to humans, was used to establish an experimental model of femoral head osteonecrosis and subsequent femoral head collapse. Focal lesions were induced in 20 adult male emus using an alternating liquid nitrogen freezing and radiofrequency heating insult. At 2, 4, 8, 12 and 16 weeks post-surgery, hip magnetic resonance imaging (MRI) was performed. Before the emus were sacrificed, barium sulphate was infused to the lower extremity to study blood vessel distribution patterns. Femoral samples were scanned by micro-computed tomography (micro-CT) and evaluated histologically. Hip MRI showed changes from broad oedema to femoral head collapse. Emus developed a crippled gait from post-operative week 6. Micro-CT scans and histology showed human-like osteonecrotic changes with an impaired local blood supply. The protocol resulted in consistent full-range osteonecrosis of the femoral head that may serve as a model for testing potential treatments.     

Amphiphilic diblock copolymer of hydrophilic-functionalized lactone and lactide via switchable organocatalytic polymerization

Main-chain degradable amphiphilic diblock copolymers composed of a hydrophilic-functionalized polyester and PLA were facilely prepared by one-pot ring-opening polymerization (ROP) via actively manipulating the catalytic states of an acid–base catalytic system. The resultant block copolymers showed low critical micelle concentration (CMC) in water and were capable of forming stable micelles with optimal hydrodynamic particle size (average diameter 83 nm) and narrow particle distribution.

Main-chain degradable amphiphilic diblock copolymers prepared by one-pot ring-opening polymerization via actively manipulating catalytic states of an acid–base catalytic system were capable of forming stable micelle with optimal particle size.

Amphiphilic block copolymers have many important applications in the life sciences, especially in drug delivery. They are able to self-assemble into micelles or polymersomes which are extensively exploited as vehicles for encapsulation and delivery of bioactive reagents. Hydrophobic blocks provided lipophilic compartments or cores for encapsulation of highly hydrophobic therapeutics. Polyesters, especially polylactide (PLA), are widely used as the hydrophobic segments of the copolymers for drug delivery due to their good biodegradability, biocompatibility and renewability.¹ Hydrophilic blocks form a fully hydrated outer shell for dispersion and reducing bio-molecule attachment. So far, water soluble poly(ethylene glycol) (PEG) is probably the mostly used hydrophilic segment in constructing copolymers for medical applications,² due to its good water solubility and resistance to the adsorption of bio-molecules in plasma. Many PEG-b-polyester amphiphilic block copolymers have been synthesized and extensively studied as delivery platforms.³ However the inherent non-biodegradable issue of PEGs has caused increasing concerns.^4,5 Though, high molecular weight PEGs (over 40 kDa) are considered to be metabolically inert, their excretion rates are significantly reduced with increase of molecular weight.⁶ Evidences have emerged showing that high molecular weight PEGs can accumulate and cause vacuolation in the liver, kidney, spleen and tissues after administration.^7,8 Growing concerns on bioaccumulation and cytoplasmic vacuolization issues of PEG prompted efforts of searching alternatives of PEG. We have recently reported facile preparation of well-defined functional poly(δ-valerolactone) (PFVL) with oligo(ethylene glycol) methyl ether (OEGME) pendant groups and demonstrated that this functional PVL was highly hydrophilic and fully comparable with PEGs in terms of bio-compatibility and capabilities of resistance to non-specific protein adsorption, which made it a promising biomaterial as fully degradable version of PEG for applications in life science.⁹ The excellent protein resistant properties of this hydrophilic polyester led to our further investigation into the feasibility of using PFVL as an alternative of PEG to construct polymeric nano-carriers for drug delivery. As proof of concept, we set out to synthesize well defined amphiphilic diblock copolymers, PFVL-b-PLA, with our functional PFVL as the hydrophilic segments and PLA as the hydrophobic blocks, and investigate the self-assembly behaviors of these diblock copolymers.Conventionally, PEG/polyester copolymers are prepared in a multi-step process which involves isolation and purification of one block before other blocks are installed to the end(s) of the first block by polymerization or by covalent conjugation. This multi-step process is time consuming and more importantly often results in loss of polymer yield and broad polydispersity.¹⁰ On the other hand, one-pot polymerization methods such as sequential monomer feeding are more efficient and can provide better control over the polymerization processes, which is highly desirable in preparation of copolymers. Though many organometallic catalysts have been successfully used to prepare copolymers by ROP of lactones and lactide,^11,12 metal-free organocatalysts are generally preferred in preparation of copolymers intended for biomedical applications due to concerns of the possible residual metallic catalyst in polymer product though not all organocatalysts are fully biocompatible.^13,14 In our previous study, it was found that diphenyl phosphate (DPP) was the most efficient catalyst among other organocatalysts screened for polymerization of δ-valerolactone with oligo(ethylene glycol) functional group under ambient conditions.⁹ Traditional one-pot synthesis of copolymers usually requires a common catalyst that works with high efficiency for all monomers of individual blocks. Unfortunately, in our case, DPP, a weak organic Brønsted acid, works efficient for our functional lactone monomers by electrophilic activation but are almost inactive for lactide which requires basic or nucleophilic activation.^15,16 Then, we noticed that Hedrick group recently reported a rather surprising discovery that a equimolar mixture of 1,8-diazabicyclo[5.4.0]-undec-7-ene (DBU) and benzoic acid (BA) which was usually used in excess to quench activity of DBU at the end of ROP of lactide turned out to be a better catalyst than DBU itself in terms of promoting well controlled ROP of lactide under mild condition.¹⁷ It was proposed that an ion pair catalyst system was formed from the mixture of BA and DBU (1 : 1, molar ratio) and a dual-activation mechanism might be involved.^18,19 Specifically, the protonated DBU cation was believed to be able to activate the initiating/propagating hydroxyl groups and benzoate anion concurrently activate the monomer carbonyl in ROP of LA.¹⁷ More intriguingly, it was found that the addition of 2 or more equivalents of BA could lead to complete deactivation of this BA/DBU ion pair catalyst system.¹⁷ Inspired by this discovery, we envisioned that the equimolar BA/DBU ion pair catalyst could be employed to efficiently prepare well defined PLA as the first block then, subsequently, two equivalents of DPP could be added to the reaction mixture to deactivated the BA/DBU ion pair and switch catalytic mode of the catalyst from being “lactide-active” to “lactide-inactive” and “lactone-active”. Thus, the newly added DPP would play double roles: (1) 1 equivalent of DPP would fully deactivate the BA/DBU ion pair (pK_a of benzoic acid, 4.204, is similar to pK_a of DPP, 3.88); (2) the other equivalent of DPP would function as catalyst for ROP of functional δ-valerolactones. Herein, we report one-pot preparation of amphiphilic PFVL-b-PLA diblock copolymers via active switch of activating states of a ROP catalyst complex. The self-assembly of the resultant amphiphilic copolymers in water was then investigated and found them readily form stable micelle structures with ideal particle size in water.As depicted in Scheme 1, PLA, the hydrophobic segment of the amphiphilic copolymers, can be facilely prepared by well controlled ROP of lactide with BA/DBU (1 : 1) as a bi-functional catalyst. And switching of catalyst states from being lactide active to lactone active is realized by introducing DPP into the reaction mixture. The performance of the catalyst complex in different active states was evaluated by homo-polymerization before employing this catalytic switching strategy in block copolymer preparation. As summarized in Scheme 1. Briefly, the ROP of lactide was carried out with benzyl alcohol as initiator and BA/DBU (1 : 1) complex as catalyst and with a [BnOH]₀/[catalyst]₀ ratio of 100 : 1 at 36 °C. While lactide conversion reaching 90%, DPP (3 equivalents with regard to BnOH) was introduced to the reaction solution to “turn-off” lactide-active mode of the catalyst complex and switch to lactone-active mode for the ROP of the incoming function lactone monomers. When the conversion of the functional lactone reached 85%, the reaction was quenched by addition of an excess amount of triethyl amine. Following this protocol, block copolymers with various block length were successfully obtained (entry 5–8) with M_n values close to theoretical ones and fairly narrow molecular weight distribution (PDI, 1.1–1.3, Fig. S2^†), which proved that this sequential addition protocol based on facile catalytic mode switching was an efficient strategy for one-pot preparation of block copolymer of lactide and the functional lactone.Open in a separate windowScheme 1One-pot synthesis of functional lactone-b-PLA diblock copolymer through catalytic activity switching.Experimental conditions and characterization of the homopolymers and copolymers^a

Effect of hydrophilic block end groups and block junction on block copolymer self-assembly in solution

Recent research suggests that the end groups of polymers can affect their self-assembly. However, the effect of end groups on the self-assembly of block copolymers in solution remains unclear, and thus far, only micelle–vesicle transformations have been achieved via end-group modification. Herein, we report that hydrophilic block end groups and the junction between two blocks can affect the solution self-assembly of block copolymers, leading to the formation of different morphologies, including vesicles, cubosomes, and hexosomes. Poly(ethylene glycol)-b-polystyrene (PEG-b-PS) with hydroxyl, methoxy, azido, or amino groups at the PEG chain ends was synthesized and self-assembled in solution via the cosolvent method. As a result, the morphology of the block copolymers transformed from vesicles to hexosomes upon increasing the end-group hydrophobicity. In addition, a morphological transition from cubosomes to vesicles was observed upon changing the junction from a triazole to an amide, and the interaction between the solvent and end groups significantly affected the self-assembly behavior.

Recent research suggests that the end groups of polymers can affect their self-assembly.     

pH-Tolerant giant vesicles composed of cationic lipids with imine linkages and oleic acids

Giant vesicles (GVs) have attracted attention as functional materials because they can encapsulate both hydrophilic and hydrophobic compounds. For next generation functional GVs, both tolerance and stimuli-sensitivity are needed. So far, vesicles tolerant to acidic or basic conditions were generated using a mixture of cationic lipids and fatty acids. Here, to create functional GVs that are tolerant to a wide pH range but sensitively respond at below a specific pH, the behaviour of GVs composed of a cationic lipid with an imine bond and oleic acid was investigated. Even though the GVs prepared by the film swelling method were tolerant to strongly acidic conditions, GVs without oleic acid gradually shrank, accompanied by the generation of oil droplets at the same pH. ¹H NMR analysis revealed that during hydration of the film, the imine bond hydrolysed to provide a cationic surfactant and an oil component in the presence of oleic acid due to its own Lewis basicity, suggesting the dissociation of oleic acid. The results of fluorescence spectroscopy using an environment-responsive probe and IR spectroscopy indicated that the GV tolerance originated from the intermolecular interactions of cationic lipids and anionic oleate.

Giant vesicles composed of cationic lipids having an imine linkage and oleic acid were stable at strong acidic conditions.     

Perfluoroalkylated alternating copolymer possessing solubility in fluorous liquids and imaging capabilities under high energy radiation

A highly fluorinated alternating polymer, P(R_FMi-St), possessing improved thermal properties and patterning capabilities over perfluoroalkyl polymethacrylates under high energy radiation was achieved with semi-perfluorododecyl maleimide (R_FMi) and styrene (St). R_FMi could be synthesised efficiently via a Mitsunobu reaction condition and copolymerised with St by free radical and reversible-deactivation radical polymerisation protocols. P(R_FMi-St) showed a satisfactory glass-transition temperature (108 °C) and intermolecular cross-linking behaviour under electron-beam and commercially more important extreme UV (λ = 13.5 nm) irradiation. The exposed regions lost their solubility, resulting in the successful formation of mechanically non-deteriorated negative-tone images down to 50 nm. In addition, P(R_FMi-St) could be solution-processed with chemically non-damaging fluorous liquids, which enabled the polymer to be applied effectively on top of an organic semiconductor layer as a dielectric material (dielectric constant 2.7) for the organic field-effect transistor fabrication.

A highly fluorinated alternating copolymer, P(R_FMi-St), possessing patterning capabilities under high energy radiation was achieved with semi-perfluorodecyl maleimide and styrene.     

Oriented self-assembly of metal–organic frameworks driven by photoinitiated monomer polymerization

The self-assembly of metal–organic frameworks (MOFs) is crucial for the functional design of materials, including energy storage materials, catalysts, selective separation materials and optical crystals. However, oriented self-assembly of MOFs is still a challenge. Herein, we propose a novel strategy to drive oriented self-assembly of MOF polyhedral particles at the water–liquid interface by photoinitiated monomer polymerization. The MOF polyhedral particles self-assemble into ordered close-packed structures with obvious orientation in the polymer film, and the orientation is determined by the casting solvent on the water surface. The prepared large-area MOF polymer films show a Janus structure, containing a MOF monolayer and a polymer layer, and can be easily transferred to a variety of substrates. In addition, mixed MOF particles with different sizes and morphologies can also be assembled by this method. This novel method can be foreseen to provide a powerful driving force for the development of MOF self-assembly and to create more possibilities for utilizing the anisotropic properties of MOFs.

The self-assembly of metal–organic frameworks (MOFs) is crucial for the functional design of materials, including energy storage materials, catalysts, selective separation materials and optical crystals.     

Novel amphiphilic graft block azobenzene-containing copolymer with polypeptide block: synthesis,self-assembly and photo-responsive behavior

Well-defined amphiphilic graft block azobenzene-containing copolymer with polypeptide block was synthesized via a combination of copper-mediated atom transfer radical polymerization (ATRP), ring-opening polymerization and click reaction. The alkyne-terminated poly[6-(4-methoxy-azobenzene-4′-oxy)hexyl methacrylate] (PAzoMA) was synthesized by ATRP with a bromine-containing alkyne bifunctional initiator, and the azido-terminated poly(γ-2-chloroethyl-l-glutamate) (PCELG) was synthesized by ROP of γ-2-chloroethyl-l-glutamate-N-carboxyanhydride (CELG-NCA), then the two homopolymers were conjugated by click reaction to afford block azobenzene-containing copolymer PAzoMA-b-PCELG. The chloro groups in PCELG block were transformed into azido groups via azide reactions, and the alkyne-terminated MPEG was grafted to the polypeptide block to afford the final product PAzoMA-b-poly((l-glutamate)-graft-methoxy poly(ethylene glycol)) (PAzoMA-b-(PELG-g-MPEG)) by click reaction. Giant vesicles (micrometer size) were obtained from the amphiphilic graft block copolymer PAzoMA-b-(PELG-g-MPEG) through a solution self-assembly due to the rigid PAzoMA chains and polypeptide chains with the α-helical structure. The investigation of the photo-isomerization behavior of PAzoMA-b-(PELG-g-MPEG) in solution and in vesicular solution showed trans–cis isomerization in solution was quicker than that in vesicular solution and azobenzene J-aggregates in the vesicle solution were only observed. The formation mechanisms of the vesicles were also explored. The research results may provide guidelines for the study of complex copolymers containing different types of rigid chains.

Giant vesicles (micrometer size) were prepared from novel amphiphilic graft block azobenzene-containing copolymer with polypeptide block synthesized via a combination of ATRP, ROP and click reaction.     

Synthesis of polynorbornadienes by ring-opening metathesis polymerization and their saturated derivatives bearing various ester groups and carboxyl groups

Various symmetric and non-symmetric polynorbornadienes having a variety of ester groups and carboxyl groups were synthesized by ring-opening metathesis polymerization (ROMP) with Grubbs'' third generation catalyst (G3 or [Ru]-III catalyst) in a controlled living manner from half-esters prepared by the selective monohydrolysis of symmetric diesters that we previously reported. The half-esters thus obtained can be directly submitted to ROMP with the G3 catalyst, leading to mostly the trans structure and narrow polydispersity indexes. The subsequent hydrogenation yielded saturated polymers, improving the thermostabilities according to the T⁵_d results. Our selective monohydrolysis reactions combined with ROMP initiated by the G3 catalyst have proven to be an efficient tool for the production of a variety of homopolymers with well-controlled structures in a living manner.

Polymer libraries were synthesized in a controlled living manner from half-esters efficiently prepared by the selective monohydrolysis of symmetric diesters.     

Effects of cholesterol on the anionic magnetite nanoparticle-induced deformation and poration of giant lipid vesicles

We have investigated the effects of cholesterol on the deformation and poration of giant unilamellar vesicles (GUVs) induced by anionic magnetite nanoparticles (NPs). Negatively charged lipid, neutral lipid, and cholesterol were used to prepare the charged GUVs (surface charge density of membranes – 0.16 C m⁻²), while only neutral lipid and cholesterol were used to prepare the neutral GUVs. Cholesterol content varied from 0 to 40 mole% for preparing the biologically relevant membranes. The degree of deformation has been characterized by compactness, the value of which remains at 1.0 for spherical GUVs. The value of compactness increases with time for both membranes, but this increase depends on cholesterol content. The average compactness decreases with cholesterol content, and at 60 min, the values are 1.280 ± 0.002 and 1.131 ± 0.010 for 0 and 40 mole% cholesterol containing charged GUVs. The average compactness is relatively lower for neutral GUVs for the corresponding cholesterol. Membrane poration has been investigated by the leakage of calcein, which indicates a two-state transition model. The fraction of deformation is higher for charged GUVs than for neutral ones, while the fraction of poration shows the opposite result. Both the fractions decrease with cholesterol content.

Cholesterol inhibits the anionic magnetite nanoparticles-induced deformation of charged and neutral giant lipid vesicles and lipid membrane poration of these vesicles.     

Amphiphilic copolymer self-assembly of magnetic nanoparticles for construction of magnetically responsive photonic crystals based on steric hindrance

Herein, a facile, simple and rapid self-assembly of magnetic colloidal nanoparticles (MCNPs) to build magnetically responsive photonic crystals (MRPCs) was devolved. A nonionic amphiphilic random copolymer poly(styrene-co-vinylpyrrolidone) P(St-co-VP) with the monomer molar ratio of 1 : 9 was used not only as an emulsifier for miniemulsion self-assembly of Fe₃O₄ magnetic nanoclusters, but also as the coating material on the magnetic nanoclusters through itself assembly. The self-assembly of the magnetic nanocluster and the polymer coating were completed simultaneously without another polymerization process. The characterization of the MCNPs and the optical properties of the MRPCs were investigated in details. TEM showed that the MCNPs had regular spherical structures with an average diameter of 104.6 nm (RSD = 13.9%, n = 100). P(St-co-VP) self-assembly coating was confirmed by IR and XPS, and thermogravimetric analysis showed that the magnetite content was 76.15%. The large content of magnetite and the thin coating of the copolymer gave MCNPs the high saturated magnetization (M_s) of 52.60 emu g⁻¹. Under an external magnetic field, the MCNPs could assemble MRPCs instantaneously and reversibly. The structural color covered entire visible spectrum by tuning the strength of the external magnetic field. On basis of the steric hindrance from neighboring PVP stretching chains, rather than electrostatic repulsion or solvation layer to counterbalance magnetic attraction, the MRPCs could tolerate the electrolyte as high as 0.10 mol L⁻¹ and the variance of pH from 2.0–12.0. The stability of P(St-co-VP) self-assembly coating was testified through the invariability of the structural color of MRPCs after repeated washing, as well as the recovery of structural color after removing the electrolytes.

One-step self-assembly of magnetic nanoparticles with amphiphilic copolymer for construction of magnetically responsive photonic crystals based on steric hindrance.     

Synthesis and self-assembly of a novel amphiphilic diblock copolymer consisting of isotactic polystyrene and 1,4-trans-polybutadiene-graft-poly(ethylene oxide)

Herein, a novel amphiphilic diblock copolymer consisting of isotactic polystyrene (iPS) and 1,4-trans-polybutadiene-graft-poly(ethylene oxide) (1,4-trans-PBD-g-PEO), iPS-b-(1,4-trans-PBD-g-PEO), was synthesized by the combination of living coordination copolymerization and graft copolymerization. iPS-b-1,4-trans-PBD was firstly synthesized via sequential monomer addition in the presence of 1,4-dithiabutandiyl-2,2′-bis(6-cumenyl-4-methylphenoxy) titanium dichloride (complex 1) activated by triisobutyl aluminum modified methylaluminoxane (MMAO). Moreover, hydroboration of double bonds in the 1,4-trans-PBD blocks were performed with 9-borabicyclo[3.3.1]nonane (9-BBN) and subsequent oxidation by NaOH/H₂O₂ to form hydroxyls. Consequently, PEO was grafted into the hydroxylated 1,4-trans-PBD block in terms of ring-opening polymerization of ethylene oxide with potassium/naphthalide as initiatior. We also described solvent-evaporation-induced self-assembly of iPS-b-1,4-trans-PBD in n-dodecane and iPS-b-1,4-trans-PBD-g-PEO in aqueous solution, which were selective solvent for 1,4-trans-PBD and for 1,4-trans-PBD-g-PEO blocks, respectively. In these cases, tetrahydrofuran (THF) was used as good and volatile solvent. These resultant iPS-containing diblock copolymers could self-assemble into spherical nano-micelles with an iPS core as amorphous agglomeration or a very low degree of crystallinity resulting from slow crystallization rate and nanoconfinement. In addition, after isothermal crystallization of iPS in the micellar cores self-assembled in n-dodecane at 120 °C for 3 hours, the micellar morphology changed from sphere-like to platelet-like. It was believed that isothermal crystallization of iPS induced the deformation of the micelles.

Herein, a novel amphiphilic diblock copolymer consisting of isotactic polystyrene and 1,4-trans-polybutadiene-graft-poly(ethylene oxide) was synthesized and its self-assembly behavior was investigated.     

Epinephrine and norepinephrine enhance p-aminohippurate transport into basolateral membrane vesicles

The effect of exogenous l-norepinephrine (NE) and l-epinephrine (EP) on transmembrane transport of p-aminohippurate (PAH) was studied in rat proximal tubular basolateral membrane vesicles. A gradient of 50 mM Na+ (out greater than in) and preloading of vesicles with unlabeled PAH were utilized to promote the influx of [3H]PAH into the vesicles. At final concentrations of 1 microM, NE and EP each produced significant elevations in vesicle uptake of [3H]PAH. The enhancement of PAH transport by NE or EP was inhibited by either phentolamine (100 microM) or yohimbine (100 microM). Prazosin (100 microM) or atenolol (100 microM) were unable to inhibit the response to NE. Similarly, prazosin or propranolol (100 microM) were unable to inhibit the response to EP. Clonidine (1 microM) also produced a significant elevation of PAH uptake, an effect inhibited by both phentolamine and yohimbine. Basolateral Na+-K+-adenosine triphosphatase activity also was increased significantly by either NE or EP (1 microM). Both agonists produced significant elevations of PAH uptake into vesicles preloaded with ATP. However, in the absence of NE or EP, PAH uptake into ATP-loaded vesicles was not significantly greater than into control vesicles. It was concluded that NE and EP enhance Na+-coupled PAH transport and that this effect may be mediated by alpha-2 adrenergic receptors. Activation of Na+-K+-adenosine triphosphatase is a possible mechanism whereby adrenergic agonists may exert effects on Na+-coupled transport across the basolateral membrane.     

Conversion of fatty acid methyl esters into dibasic esters by metathesis and their lubricant properties

Biodiesel plants are struggling to find value added applications for fatty acid methyl esters (FAME). One option for FAME valorization would be dibasic esters, which can be transesterified with 2-ethylhexyl (2EH) or other alcohols to produce lubricant basestocks and achieve the most widespread viscosity grades VG46 and VG32. Biocatalytic, metathesis and other synthetic pathways are available to produce dibasic esters. Using a ruthenium-based catalyst, methyl oleate was converted into monounsaturated dibasic ester by metathesis and reached VG22 after transesterification with 2EH in this investigation. Synthesized 2EH esters of other dibasic acids showed distinct viscometric trends. Their correlation implied that FAME from gondoic and erucic acids should result in VG32 and VG46 respectively, if converted into 2EH dibasic esters. Pour points demonstrated excellent low temperature fluidity and resistance to heat thinning when monounsaturation was retained. Oxidative stability properties remained acceptable, volatility was lower than that of VG46 mineral oils. Mixed alcohols, acids and esters can also be used for meeting VG specifications or achieving higher biobased contents. Currently petrochemical ester basestocks dominate in high performance hydraulic fluids (HF). However, fractionation of FAME into high-erucic/gondoic esters in biodiesel plants can produce a valuable biobased feedstock for large volume manufacture of HF and other lubricants.

Monounsaturated dibasic esters were obtained by FAME metathesis and tested for viscosity, extreme temperature and other lubricant properties. Their 2EH derivatives can produce 100% bio-derived basestocks for widespread heavy duty hydraulic fluids.