BAB Type Research Articles

On the boundedness of globally F-split varieties

This paper proposes the use of F-split and globally F-regular conditions in the pursuit of BAB type results in positive characteristic. The main technical work comes in the form of a detailed study of threefold Mori fibre spaces over positive dimensional bases. As a consequence we prove the main theorem, which reduces birational boundedness for a large class of varieties to the study of prime Fano varieties.

Cyclization of PEG and Pluronic Surfactants and the Effects of the Topology on Their Interfacial Activity.

A series of cyclic surfactants were synthesized from a poly(ethylene glycol) (PEG) homopolymer and Pluronic surfactants L35, L64, P123, F68, 10R5, and 17R4, and their interfacial activity depending on the topology, chain ends, and block sequence was investigated. The cyclization was performed in a single step through etherification of the PEG homopolymer and the hydrophilic-hydrophobic-hydrophilic (ABA type) poly(ethylene glycol)-poly(propylene glycol)-poly(ethylene glycol) (PEG-PPG-PEG), while the hydrophobic-hydrophilic-hydrophobic (BAB type) PPG-PEG-PPG was cyclized via acetalization. The cyclized surfactants were rigorously characterized by nuclear magnetic resonance spectroscopy and size exclusion chromatography. Cyclization of the surfactants induced a significant decrease in the hydrodynamic volume, which was more pronounced than that of the PEG homopolymer. Surface tension (γ) measurements indicated that the interfacial activity of the cyclized surfactants is stronger than their corresponding linear precursors, due to the increase in the surfactant density at the air-water interface as a consequence of the decreased molecular occupational area (A) upon cyclization. In the case of the PEG homopolymer, A considerably decreased from 410 Å2 for the linear PEG prepolymer to 100 Å2 for the cyclized PEG product. While the effects of chain-end groups were found to be limited to surfactants of relatively small molecular weights, the influence of cyclization depended strongly on the hydrophilic/hydrophobic ratio; the higher the PEG composition the surfactants had, the larger the decrease in γ and A; in other words, stronger enhancement in the interfacial activity was observed.

Synthesis and properties of amphiphilic thermo-sensitive block copolymers

Octadecyl acrylate (ODA) as hydrophobic monomer and N-isopropylacryamide (NIPAAm) as hydrophilic monomer were chosen to synthetize the thermo-sensitive block copolymers PODAx-PNIPAAmy-PODAx (BAB-type) via reversible-addition-fragmentation chain transfer (RAFT) polymerization, the block copolymers could self-assemble to flower-like micelles in aqueous solution with hydrophobic PODA as the inner core and stabilized by hydrophilic PNIPAAm as the outer shell. The characterizations of the micelles such as surfactivity, thermo-sensitivity, micelle hydrodynamic radius (Rh) and polydispersity index (PdI) were demonstrated by surface tension technique, UV-Vis, and dynamic light scattering (DLS) measurements, respectively. The longer the hydrophilic chain was, the higher the critical micellization concentration (CMC) would be, and the higher content of the PODA was, the lower the lower critical solution temperature (LCST) would be. The average Rh remained at about 100 nm below LCST, but decreased sharply to about 42 nm and kept constant when reaching and above LCST, which meant the non-aggregation of BAB type block copolymers. The micelle was homogeneous with the small PdI within the range of research. B0.5mA24mB0.5m had the largest capacity to encapsulate lipophilic Sudan Red IV model drugs and the drug loading efficiency was 9.76%.

Computer simulation of self-assembly of cone-shaped nanoparticles

Two kinds of cone-shaped particles are designed: one with a Janus structure and the other with a sandwich structure. The effects of the cone angle and particle structure (i.e. AB type and BAB type) on the kinetic pathway and assembled structures are discussed.

Synthesis of gradient copolysiloxanes by simultaneous copolymerization of cyclotrisiloxanes and mechanism for kinetics inverse between anionic and cationic ring‐opening polymerization

ABSTRACTTrifluoropropylmethylsiloxane–phenylmethylsiloxane gradient copolysiloxanes were synthesized by anionic and cationic ring‐opening polymerization (ROP) of 1,3,5‐tris(trifluoropropylmethyl)cyclotrisiloxane ( ) and phenylmethylcyclotrisiloxane ( ). The analysis of reactivity ratios revealed that the reactivity of toward anionic ROP was higher than that of ; however, exhibited lower reactivity compared with during the cationic ROP. AB and BAB type gradient copolymers were obtained because of a difference in the reactivity of the monomers. The microstructure of copolymers was characterized by 29Si NMR spectroscopy, gel permeation chromatography, and differential scanning calorimetry. Furthermore, the mechanism for kinetics inverse of copolymerization was proposed based on the results of the optimized molecular configuration. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 835–843

Molecular Dynamics Modelling of Block-Copolymer Electrolytes with High t+ Values

Molecular Dynamics simulations of the BAB type triblock copolymer lithium poly[(4-styrenesulfonyl) (trifluoromethylenesulfonyl) imide)]-block-poly(ethylene oxide)-block-lithium poly[(4-stryrenesylfonyl) (trifluoromethanesulfonyl) imide] (P(STFSILi)-b-PEO-b-P(STFSILi)) were carried out for different simulation temperatures and B-block lengths. By covalently binding the anion to the polymer backbone, it is immobilised and the cation transference number thereby raised significantly. It was found that the Li-ion diffusion decreases exponentially with growth of the B-block length. The poly(ethylene oxide) matrix dissolves Li-ions already during the equilibration stage of the simulation, and no Li-ion diffusion pathways were identified along the STFSI branches, which significantly influence the transport properties of the material.

Charge Dependent Dynamics of Transient Networks and Hydrogels Formed by Self-Assembled pH-Sensitive Triblock Copolyelectrolytes

Triblock copolymers of BAB type were synthesized by ATRP with a poly(acrylic acid) central block and random copolymer end blocks containing both acrylic acid (AA) and hydrophobic n-butyl acrylate (nBA) units with varied composition of the B-blocks. Visco-elastic properties of these amphiphilic polymers were investigated by oscillatory shear measurements as a function of composition, concentration, temperature and pH. Whatever the composition for each polymer the terminal relaxation time and thus the viscosity increased sharply with decreasing degree of ionization of the AA units (α) and at low values self-supporting hydrogels were formed. However, the α- (respectively pH-) dependence of the terminal relaxation time as well as the critical range of α (respectively pH) where a transition between visco-elastic solutions and self-supporting hydrogels occurs strongly depend on the composition of the B-block.

The synthesis and solution behaviors of novel amphiphilic block copolymers based on d-galactopyranose and 2-(dimethylamino)ethyl methacrylate

A series of novel stimuli-responsive AB, ABA, and BAB type block copolymers based on 6-O-methacryloyl-1,2:3,4-di-O-isopropylidene-d-galactopyranose (MAIpGP:A block) and 2-(N,N-dimethylamino)ethyl methacrylate (DMAEMA: B block) were synthesized via ATRP techniques using ethyl 2-bromoisobutyrate (EBiB) as monofunctional ATRP initiator in the case of diblock copolymer and diethyl meso-2,5-dibromoadipate (DEDBA) as bifunctional ATRP initiator in the case of triblock copolymers. The PMAIpGP blocks of the AB, ABA, and BAB type linear block copolymers were converted to water soluble PMAGP blocks via deprotection process under mild acidic conditions. Both proton NMR and DLS studies demonstrated that block copolymers were temperature-sensitive, whereby the lower critical solution temperature (LCST) of polymers varied with the polymerization degrees of comonomers in the block copolymers. LCST was determined to be between ∼35°C and 55°C depending on the type and the comonomer compositions of the block copolymers. It was observed that an increase on the percentage of hydrophilic PMAGP block in block copolymer caused an increase on the LCST value as expected.

Controllable preparation and characterization of the thermosensitive block polymers

Two kinds of triblock copolymers based on N-isopropylacrylamide (NIPAAm) and ethyl acrylate(EA), PEAn-PNIPAAmm-PEAn (BAB type) and PNIPAAmm-PEAn-PNIPAAmm (ABA type) were prepared via reversible addition-fragmentation chain transfer (RAFT) polymerization. Thermosensitive block polymer of PEAn-PNIPAAmm-PEAn (BAB type) and PNIPAAmm-PEAn-PNIPAAmm (ABA type) self-assembly form flower coronal and dendritic micelles in water solution with hydrophobic PEA as the core and hydrophilic PNIPAAm as the shell, respectively. Critical micelle concentration (CMC) can be obtained by measuring the surface tension of the copolymer. The study reveals that CMC of micelles are significantly affected by the monomer weight ratios of EA/NIPAAM in block copolymer and block in the order. The higher the content of the hydrophilic block, the smaller the copolymer CMC, and ABA-type with respect to the BAB-type has a smaller CMC value. Particle size of self-assembled micelles decreased first and then rapidly increased with the temperature increasing, surfactant SDS significantly affects the particle size of the polymer. By measuring the light transmission ratio of the copolymer solution, the effect of the lower critical solution temperature (LCST) in the salt solution was investigated, and it was also found that the higher content of the hydrophilic block, the higher LCST of copolymer.

Direct synthesis of mesoporous silica presenting large and tunable pores using BAB triblock copolymers: Influence of each copolymer block on the porous structure

Mesoporous silicas with large and tunable (from 4 to 40 nm) accessible pores have been successfully synthesized using laboratory-made BAB (A: hydrophilic block, B: hydrophobic block) type triblock copolymers as templates. A direct synthesis is carried out in the absence of swelling agent and without any further treatment. The polystyrene- b–poly(ethylene oxide)- b–polystyrene (PS- b–PEO- b–PS) copolymers were synthesized using living/controlled radical polymerization. The porous structure (mesopore size, size distribution and microporous volume) was characterized using electron transmission microscopy and nitrogen sorption measurements. This study is focused on the control of the porous structure as a function of the hydrophobic PS block length and the hydrophilic block length (whilst keeping the other block length constant). It was found that when the PS block length increases: (i) the mesopore size increases linearly with PS block length which thus proffers a fine tuning of the pore diameter from 4 to 40 nm, (ii) the micropore volume decreases. When the PEO block length increases, (i) the mesopore size decreases (ii) the micropore volume increases. All these results were explained considering (i) that both PS and PEO block lengths have an influence on the degree of stretching of the PS chains, thus on the micellar core radius (ii) that the mesopore size is directly connected to the micellar core radius, i.e. that PEO chains do not directly participate to mesoporosity (due to its particular loop configuration) but only to microporosity.

日本海竹島海山 (仮称) のかんらん岩捕獲岩の成因とその意義

The Sea of Japan is one of the back-arc basins distributed around the western rim of the Pacific. Nature of the plume for back-arc basin (= BAB) opening is unknown partly because petrological characteristics of the BAB mantle are not well known compared with mid-ocean ridge (= MOR) mantle. Peridotite xenoliths in an alkali basalt dredged from the Takeshima seamount (tentative name), ca. 230 km to the north of Oki islands, are examined to clarify the petrological feature of the Japan-Sea mantle. They are spinel-bearing lherzolite to harzburgite with equigranular to porphyroclastic textures. They can be classified into two types (Type 1 and Type 2 peridotites) in terms of REE (= rare earth elements) patterns of clinopyroxene (= cpx). Type 1 peridotites (Cr# of spinels, 0.4-0.5) are similar to abyssal peridotites in terms of major element chemistry and middle- to heavy-REE concentrations of cpx. The cpx in the former shows slight enrichment of LREE (= light REE), which is apparently due to metasomatism by slab-derived fluids/melts. Type 2 peridotites have high-REE cpx with flat to slightly LREE-enriched patterns, and are quite similar to subcontinental peridotites obtained as xenoliths from China. The southern part of the Sea of Japan was formed by mainly thinning and rifting of the continental lithosphere. Type 2 peridotites are a remnant of the continental lithospheric mantle. Chemical characteristics of BAB basalts and Type 1 peridotites indicate that open-system melting of peridotite affected by a flux from the downgoing slab was involved in the Japan-Sea opening.

ABA and BAB type triblock copolymers of PEG and PLA: A comparative study of drug release properties and “stealth” particle characteristics

We synthesized two types of triblock copolymers containing PEG and PLA as controlled release carriers of hydrophobic drugs: these are the ABA type (PLA–PEG–PLA) and the BAB type (PEG–PLA–PEG). These polymers are amphiphilic and can form nanomicelles (40–200 nm) in aqueous medium. On the surface of PLA–PEG–PLA (ABA) type nanomicelles, the PEG content was enhanced somewhat over the bulk amount; whereas in the PEG–PLA–PEG (BAB type), surface segregation was much higher. The copolymers tested can entrap 35% of paclitaxel by weight on the average. In general, the diffusion-controlled release of paclitaxel is slower for the BAB polymers; furthermore, the actual release rates are influenced by the PLLA lengths in the BAB copolymers. Surface PEG contents influence the “stealth” characteristics of the nanomicelles. Compared with PLA particles, all nanomicellar particles tested, of both BAB and ABA types, showed a four-fold reduction in monocyte cell uptake, with the BAB type copolymer exhibiting a lesser uptake.

On the conformation of the hydrophilic (B) chains in ABA and BAB type triblock copolymers

SANS [Sz. Vass, K. Haimer, G. Meier, M. Klapper, S. Borbély, Colloid Polym. Sci. 280 (2002) 245] and SAXS studies of poly(methyl methacrylate)- block-poly(sodium acrylate)- block-poly(methyl methacrylate), pMMA/pNaA/pMMA (ABA), and pNaA/pMMA/pNaA (BAB) triblock copolymer micelles resulted in essentially different types of scattering patterns. Due to the difficulties in fitting the Pedersen–Gerstenberg model [J.S. Pedersen, M.C. Gerstenberg, Macromolecules 29 (1996) 1363], the question arose whether the conformation of the hydrophilic chains is the same for the two block-sequences. From the analysis of the tails of SAXS patterns from ABA and BAB polymer solutions we concluded that the hydrophilic chains are Gaussian with nearly the same Kuhn length, without regard to the block sequence.

Synthesis and in vitro drug release behavior of amphiphilic triblock copolymer nanoparticles based on poly (ethylene glycol) and polycaprolactone

Novel BAB type amphiphilic triblock copolymers consisting of poly (ethylene glycol) (PEG) (B) as hydrophilic segment and poly ( ε-caprolactone) (PCL) (A) as hydrophobic block were prepared by coupling reaction using l-lysine methyl ester diisocyanate (LDI) as the chain extender. The triblock copolymers obtained were characterized by FT-IR, 1H NMR, GPC, and DSC. Core-shell type nanoparticles were prepared by nanoprecipitation method and below 100 nm nanoparticles were obtained due to their specific structure. Transmission electron microscopy image demonstrated that these nanoparticles were spherical in shape. Stability of the nanoparticles in biological media was evaluated. Poorly water-soluble anticancer drug 4′-demethyl-epipodophyllotoxin (DMEP) was chosen for controlled drug release because it was easily encapsulated into polymeric nanoparticles via hydrophobic interaction. In vitro release behavior of DMEP from polymeric nanoparticles was investigated, the results showed that the drug release rate can be modulated by the variation of the copolymer composition.

Preparation and Reconstitution of Core-shell Type Nanoparticles of Poly(ε -caprolactone)/Poly(ethyleneglycol)/Poly(ε -caprolactone) Triblock Copolymers

One of the improtant characteristics of core-shell type nanoparticles is the long-term storage and reuse as an aqueous injection solution when required. For this reason, reconstruction of lyophilized core-shell type nanoparticles is considered to be essential . BAB type triblock copolymers differ from AB type diblock copolymers, which contain the A block as a hydrophilic part and the B block as a hydrophobic part. by not being easily redistributed into phosphate-buffered saline (PBS, pH 7.4, 0.1 M). Therefore, lyophilized core-shell type nanoparticles of CEC triblock copolymer were reconstituted using a somication process with a bar-type sonicator in combination with a freezing-thawing process. Soncation for 30s only resuspended CEC nanoparticles in PBS; their particle size distribution showed a monomodal pattern with narrow size distribution. The bimodal size distribution pattern and the aggregates were reduced by further sonication for 120 s but these nanoparticles showed a wide size distribution. The initial burst of drug release was increased by reconstitution process. The reconstitution of CEC core-shell type nanoparticles by freezing-thawing resulted in trimodal distribution pattern and formed aggregates, although freezing-thawing process was easier than sonication . Drug release form CEC nanoparticles prepared by freezing-thawing was slower than from the original dialysis solution. Although core-shell typenanoparticles of CEC triblock copolymers were not easily performed. Cytotoxicity testing of core-shell type nanoparticles of CEC-2 triblock copolymers containing clonazepam (CNZ) was performed using L929 cells. Cytotoxicity of CNZ was decreased by incorporation into nanoparticles.

Flower type microgels: 1. Synthesis of the microgels

Poly(2-vinyl pyridine-b-styrene-b-2-vinyl pyridine) BAB type block copolymers were synthesized by anionic living polymerization. The micelle formation of these BAB type triblock copolymers was carried out in toluene and toluene/cyclohexane mixture, and estimated with dynamic light scattering for the polymer solutions. Poly(2-vinyl pyridine) sequences in core part of the polymer micelles of the BAB type block copolymers were crosslinked with 1,4-diiodobutane. Upon crosslinking, no macrogelation was observed and the poly(2-vinyl pyridine) core-polystyrene shell type spherical microgels were synthesized.

Synthesis and characterization of poly(dimethylsiloxane)-poly(ethylene oxide)-heparin CBABC type block copolymers

Heparin and poly(ethylene oxide) were coupled to a central anchoring block of poly(dimethylsiloxane) in order to investigate its blood compatible properties. Diamino telechelic poly(dimethylsiloxane) (PDMS-(NH2)2, Mw = 20,000) was first modified to isocyanate functionalities using toluene 2,4-diisocyanate. This modified PDMS was then coupled to diamino-telechelic poly(ethylene oxide) (PEO-(NH2)2, Mw = 2000, 4000, 6000) to create BAB type copolymers having terminal free amino groups. These amino groups were covalently coupled to heparin containing terminal aldehyde groups using sodium cyanoborohydride to yield a bioactive, CBABC type block copolymer. The physical characterization of these copolymers was performed with IR, NMR, sulphur elemental analysis, Wilhelmy plate contact angle, and differential scanning calorimetry (DSC). CBABC block copolymer surfaces demonstrated heparin bioactivity in in vitro evaluation, and improved nonthrombogenic properties during ex vivo A-A shunt experiments.

Block and graft copolymers of 2-oxazolines

This paper describes our recent developments of block and graft copolymers prepared by the cationic ringopening polymerization of 2-oxazolines. First, the mechanistic aspects of polymerization are mentioned, in which terms of “electrophilic and nucleophilic polymerizations” are proposed. Then, preparations and properties of poly(N-acylethylenimine) chains from 2-oxazoline monomers are described. They are (i) AB and BAB type block copolymers of 2-oxazolines for nonionic polymer surfactants, (ii) poly[(N-acetylethylenimine)-b-(oxyethylene)] for anti-electrostatic agents, (iii) cellulose diacetate having poly(N-acylethylenimine) graft chain for “compatibilizer” with commodity polymers, and (iv) polyethylene/vinyl acetate copolymer having poly(N-acylethylenimine) graft chain for blood-compatible polymeric materials.

Charge mosaic membrane with a microstructure of poly(styrene‐b‐4‐vinylpyridine)

AbstractWell defined AB and BAB type poly[styrene(ST)‐b‐4‐vinylpyridine(4VP)]s were prepared by anionic living polymerization in tetrahydrofuran (THF) at −78°C. Casting AB and BAB type poly(ST‐b‐4VP)s with a composition of about 50 mol% PST from 1,1,2‐trichloroethane (TCE) produced specimens with lamellar microdomain structures. Quaternization of P4VP and sulfonation of PST domains (lamellar and spherical structures), accompanied by each domain fixing, were carried out under various reaction conditions. The piezodialysis of the prepared charge mosaic membrane with its lamellar microdomain structure was measured from a sodium chloride (NaCl) aqueous solution. The results are discussed in some detail.

Synthesis and morphology of BAB type poly(styrene‐b‐2‐methyl‐2‐oxazoline) block copolymers

AbstractWell defined BAB‐type poly[styrene(ST)‐b‐2‐methyl‐2‐oxazoline(MeOz)] was prepared by the cationic polymerization of α,ω‐p‐toluenesulfonic acid ester‐terminated PST (PST‐BTs) as an initiator. Alkaline hydrolysis of this block copolymer was carried out under various reaction conditions to obtain BAB‐type poly[ST‐b‐ethylene imine(EI)]. Morphologies of these block copolymer specimens cast from several solvents were observed by electron microscope. The results are discussed in some detail.