Synthesis and aqueous solution properties of functionalized and thermoresponsive poly(D,L-lactide)/polyether block copolymers

Tri- and pentablock amphiphilic copolymers containing hydrophobic poly(D,L-lactide) block(s) and hydrophilic polyethers were synthesized in order to obtain new precursor architectures suitable for drug delivery systems. Polyglycidol-6-poly(ethylene oxide)-b-poly(D,L-lactide) possess high hydroxyl functionality provided by the linear polyglycidol block. Thus very stable hydroxyl functionalized micelles in aqueous media were obtained. On the other hand poly(D,L-lactide)-b-poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide)-b-poly(D,L-lactide) form temperature sensitive aggregates. The copolymers obtained were analyzed by SEC and NMR, and their aqueous solution properties were followed by cloud point measurements and determination of critical micellization temperature. TEM was used for particles visualization.     

Low temperature ATRP of POSS-MA and its amphiphilic pentablock copolymers

A low temperature ATRP of methacryloisobutyl POSS (POSS-MA) is carried out, using poly(propylene glycol) (PPG)-based macroinitiator, in toluene with CuCl/PMDETA as the catalyst system, generating well-defined P(POSS-MA)-b-PPG-b-P(POSS-MA) triblock copolymer with Р~ 1.1. The semilogarithmic kinetic plot reveals first-order kinetics and the dispersity is observed to decrease as the reaction progresses—an indication of the controlled behavior of the polymerization. To assess the chain-end fidelity of the produced block copolymer, chain extension is carried out with oligo(ethylene glycol methacrylate) (OEGMA) that afforded water-soluble P(OEGMA)-b-P(POSSMA)-b-PPG-b-P(POSSMA)-b-P(OEGMA) pentablock copolymers. The SEC profiles suggest a quantitative initiation by the macroinitiator. By varying the monomer to initiator molar ratio, block copolymers with various P(OEGMA) chain lengths, ranging from 19 to 58 units on each side have been achieved with relative lower dispersity (Р< 1.4). Kinetic analysis of the ATRP of OEGMA, with P(POSSMA)-b-PPG-b-P(POSSMA) as the macroinitiator, suggests first-order kinetics and controlled nature of the polymerization. The PPG and P(OEGMA) segments impart a thermosensitive character to the obtained water-soluble amphiphilic hybrid block copolymers; hence they display temperature-dependent self-assembly behavior in aqueous medium.     

Preparation and stabilization of silver nanoparticles by a thermo-responsive pentablock terpolymer

Thermo-reversible silver nanoparticles (Ag-NPs) were prepared by the sodium borohydride reduction of silver nitrate (AgNO₃) in the presence of a pentablock terpolymer, poly(N-isopropylacrylamide)-b-poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide)-b-poly(N-isopropylacrylamide) (PNIPAM₁₅₀-PEO₁₃₆-PPO₄₅-PEO₁₃₆-PNIPAM₁₅₀). The pentablock terpolymer-stabilized silver nanoparticles (Pentablock-S-Ag) were characterized by UV-VIS spectroscopy, X-ray diffraction (XRD), thermal gravimetric analysis (TGA) and transmission electron microscopy (TEM). At temperatures below lower critical solution temperature (LCST) of Pentablock-S-Ag solutions, the obtained Ag-NPs are well-dispersed with spherical shape, and their sizes mainly depend upon the molar ratios of pentablock terpolymer to AgNO₃; at temperatures above LCST, the size of Ag-NPs decreases and their aggregates are observed due to the collapse and shrinkage of the thermo-responsive PNIPAM and PPO segments. A reversible dispersion-aggregation process upon recyclically changing temperature is also observed.     

Novel supramolecular block copolymer containing organic–inorganic pentablock copolymer by ATRP of styrene and vinyl acetate using polydimethylsiloxane/cyclodextrin inclusion complexes as macroinitiator

Organic–inorganic pentablock copolymers have been synthesized via atom transfer radical polymerization (ATRP) of styrene (St) and vinyl acetate (VAc) monomers at 60 °C using CuCl/N,N,N′,N″,N″-pentamethyldiethylenetriamine as a catalyst system initiated from boromoalkyl-terminated poly(dimethylsiloxane) (PDMS)/cyclodextrins macroinitiator (Br-PDMS/γ-CD). Br-PDMS-Br was reacted with γ-CD in different conditions with inclusion complexes being characterized through hydrogen nuclear magnetic resonance (¹H NMR) and differential scanning calorimetry (DSC). Resulting Br-PDMS-Br/γ-CD inclusion complexes were taken as macroinitiators for ATRP of St and VAc. Well-defined poly(styrene)-b-poly(vinyl acetate)-b-poly(dimethylsiloxane/γ-cyclodextrin)-b-poly(vinyl acetate)-b-poly(styrene) (PSt-b-PVAc-b-PDMS/γ-CD-b-PVAc-b-PSt) pentablock copolymer was characterized by ¹H NMR, gel permeation chromatograph (GPC) and DSC. There was a good agreement between the number-average molecular weight calculated from ¹H NMR spectra and that of theoretically calculated. Pentablock copolymers consisting of Br-PDMS-Br/γ-CD inclusion complex as central blocks (inorganic block) and PVAc and PSt as terminal blocks were synthesized by this technique. PSt-b-PVAc-b-PDMS/γ-CD-b-PVAc-b-PSt pentablock copolymer can undergo a temperature-induced reversible transition upon heating of the copolymer complex from white complex at 22 °C to green complex in 55 °C which characterized with XRD and ¹H NMR. XRD showed a change in crystallinity percent of St peak with changing the temperature which calculated by Origin75 software.     

Synthesis of Amphiphilic ABCBA-Type Pentablock Copolymer from Consecutive ATRPs and Self-Assembly in Aqueous Solution

Summary: A novel amphiphilic ABCBA-type pentablock copolymer with properties that are sensitive to temperature and pH, poly(2-dimethylaminoethyl methacrylate)-block-poly(2,2,2-trifluoroethyl methacrylate)-block-poly(ε-caprolactone)-block-poly(2,2,2- trifluoroethyl methacrylate)-block-poly(2-dimethylaminoethyl methacrylate) (PDMAEMA- b-PTFEMA-b-PCL-b-PTFEMA-b-PDMAEMA), was synthesized via consecutive atom transfer radical polymerizations (ATRPs). The copolymers obtained were characterized by gel permeation chromatography (GPC) and ¹H nuclear magnetic resonance (NMR) spectroscopy, respectively. The aggregation behaviors of the pentablock copolymers in aqueous solution with different pH (pH = 4.0, 7.0 and 8.5) were studied. Transmission electron microscopic images revealed that spherical micelles from self-assembly of the pentablock copolymer were prevalent in all cases. The mean diameters of these micelles increased from 34, 46, to 119 nm when the pH of the aqueous solution decreased from 8.5, 7.0, to 4.0, respectively.     

New Segmented Copolymers by Combination of Atom Transfer Radical Polymerization and Ring Opening Polymerization

Atom transfer radical polymerization (ATRP) and ring opening polymerization (ROP) were combined to synthesize various polymers with various structures and composition. Poly(ε-caprolactone)-b-poly(n-octadecyl methacrylate), PCL-PODMA, was prepared using both sequential and simultaneous polymerization methods. Kinetic studies on the simultaneous process were performed to adjust the rate of both polymerizations. The influence of tin(II) 2-ethylhexanoate on ATRP was investigated, which led to development of new initiation methods for ATRP, i.e., activators (re)generated by electron transfer (AGET and ARGET). Additionally, block copolymers with two crystalizable blocks, poly(ε-caprolactone)-b-poly(n-butyl acrylate)-b-poly(n-octadecyl methacrylate), PCL-PBA-PODMA, block copolymers for potential surfactant applications poly(ε-caprolactone)-b-poly(n-octadecyl methacrylate-co-dimethylaminoethyl methacrylate), PCL-P(ODMA-co-DMAEMA), and a macromolecular brush, poly(hydroxyethyl methacrylate)-graft-poly(ε-caprolactone), PHEMA-graft-PCL, were prepared using combination of ATRP and ROP.     

Enhanced dispersion stability of supramolecular complexes of single-walled carbon nanotubes with fluorene-based conjugated polymers

Supramolecular complexes of single-walled carbon nanotubes (SWNTs) with poly(9,9-didodecylfluorene-2,7-diyl) (PF) derivatives were prepared using a solution dispersion process. A series of novel conjugated PF polymers with carboxyl or hydroxyl end groups at both ends were synthesized by the Yamamoto-type coupling of 2,7-dibromo-9,9-didodecylfluorene using Ni(COD)₂ as a catalyst, and further end-capped with either 4-bromobenzoic acid or 4-bromobenzyl alcohol to obtain the end-functionalized PF with different terminal groups. An α-monocarboxy-ω-mono-methoxy poly(ethylene glycol) was connected to both ends of the PF-containing hydroxyl end groups to produce triblock copolymers of poly(ethylene glycol)-b-polyfluorene-b-poly(ethylene glycol) (PEO-b-PF-b-PEO). These SWNTs were completely wrapped with the conjugated polymers through π–π interactions, which enhanced the solubility of the SWNT complexes in organic media, and prevented the aggregation of the polymer–SWNT complexes into large bundles. This indicates that the dispersion stability of SWNTs is enhanced by the addition of the conjugated polymers.     

Cisplatin-loaded polymer/magnetite composite nanoparticles as multifunctional therapeutic nanomedicine

Multifunctional nanocarriers with multilayer core-shell architecture were prepared by coating superparamagnetic Fe3O4 nanoparticles with diblock copolymer folate-poly（ethylene glycol）-b-poly（glycerol monomethacrylate） （FA-PEG-b- PGMA）, and triblock copolymer methoxy poly（ethylene glycol）-b-poly（2-（dimethylamino） ethyl methacrylate）-b- poly（glycerol monomethacrylate） （MPEG-b-PDMA-b-PGMA）. The PGMA segment was attached to the surfaces of Fe304 nanoparticles, and the outer PEG shell imparted biocompatibility. In addition, folate was conjugated onto the surfaces of the nanocarriers. Cisplatin was then loaded into the nanocarrier by coordination between the Pt atom in cisplatin and the amine groups in the inner shell of the multilayer architecture. The loaded cisplatin showed pH-responsive release： slower release at pH 7.4 （i.e. mimicking the blood environment） and faster release at more acidic pH （i.e. mimicking endosome/lysosome conditions）. All of the cisplatin-loaded nanoparticles showed concentration-dependent cytotoxicity in HeLa cells. However, the folate-conjugated cisplatin-loaded carriers exhibited higher cytotoxicity in HeLa cells than non-folate conjugated cisplatin-loaded carriers.     

三嵌段共聚物PAN-b-PEG-b-PAN的合成及其自组装行为的研究

利用原子转移自由基聚合(ATRP)制得了分子量可控、分子量分布窄的聚丙烯腈-b-聚乙二醇-b-聚丙烯腈P(AN-b-PEG-b-PAN)嵌段共聚物. 通过¹H NMR, FTIR, 凝胶渗透色谱(GPC)对所得产物的结构和分子量进行了表征并通过TG和DTA考察了该嵌段共聚物的热稳定性; 运用透射电子显微镜(TEM)、荧光探针技术和动态光散射(DLS)研究了P(AN)₂₇-b-P(EG)₄₅-b-P(AN)₂₇在溶剂水中胶束的形成、结构、形貌和胶束粒径. 结果表明, 三嵌段共聚物P(AN)₂₇-b-P(EG)₄₅-b-P(AN)₂₇的热稳定性较纯聚乙二醇P(EG)好, 且柔性链PEG的引入对嵌段共聚物的放热峰位置没有显著的影响. 当改变此嵌段共聚物溶液浓度时, 该嵌段共聚物会自组装成不同形状的胶束, DLS测量的胶束粒径大于TEM观察的结果, 其临界胶束浓度(cmc)约为4.46×10^－4 g•L^－1.     

Synthesis and micelle formation of triblock copolymers of poly(methyl methacrylate)-b-poly(ethylene oxide)-b-poly(methyl methacrylate) in aqueous solution

Amphiphilic triblock copolymers of poly(methyl methacrylate)-b-poly(ethylene oxide)-b-poly(methyl methacrylate) (PMMA-b-PEO-b-PMMA) with well-defined structure were synthesized via atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA) initiated by the PEO macroinitiator. The macroinitiator and triblock copolymer with different PMMA and/or PEO block lengths were characterized with ¹H and ¹³C NMR and gel permeation chromatography (GPC). The micelle formed by these triblock copolymers in aqueous solutions was detected by fluorescence excitation and emission spectra of pyrene probe. The critical micelle concentration (CMC) ranged from 0.0019 to 0.016 mg/mL and increased with increasing PMMA block length, while the PEO block length had less effect on the CMC. The partition constant K_v for pyrene in the micelle and in aqueous solution was about 10⁵. The triblock copolymer appeared to form the micelles with hydrophobic PMMA core and hydrophilic PEO loop chain corona. The hydrodynamic radius R_h,app of the micelle measured with dynamic light scattering (DLS) ranged from 17.3 to 24.0 nm and increased with increasing PEO block length to form thicker corona. The spherical shape of the micelle of the triblock copolymers was observed with an atomic force microscope (AFM). Increasing hydrophobic PMMA block length effectively promoted the micelle formation in aqueous solutions, but the micelles were stable even only with short PMMA blocks.     

Synthesis and self-assembly of pH-responsive amphiphilic dendritic star-block terpolymer by the combination of ROP, ATRP and click chemistry

Novel pH-responsive amphiphilic dendritic star-block poly(l-lactide)-b-poly(2-(N, N-diethylamino)ethyl methacrylate)-b-poly(ethylene oxide) (DPLLA-b-PDEAEMA-b-PEO) terpolymers were synthesized by the combination of ring-opening polymerization (ROP), atom transfer radical polymerization (ATRP), and click chemistry. DPLLAOH was synthesized by ROP of l-lactide (LLA) and then reacted with propargyl 3-carboxylic-propanoate to obtain alkynyl-DPLLA. PEO-b-PDEAEMA-Br was prepared by ATRP of DEAEMA and then reacted with NaN₃ to obtain PEO-b-PDEAEMA-N₃. DPLLA-b-PDEAEMA-b-PEO was easily prepared by click chemistry of alkynyl-DPLLA and PEO-b-PDEAEMA-N₃. DPLLA-b-PDEAEMA-b-PEO can assemble into micelles in water with PLLA segments as core and PEO segments as corona. The hydrophilicity/hydrophobicity of PDEAEMA can be adjusted with the alteration of pH values. Therefore, PDEAEMA segments form core or corona of micelles at pH ? 7 or pH < 7. Due to the pH-responsive property of PDEAEMA and unique structure of terpolymer, the size and conformation of the micelles can be changed to some extent by altering the pH values of solutions.     

ATRP of Silylated Glycerol Monomethacrylate in Organic Medium for Convenient Synthesis of Amphiphilic Copolymers

A synthetic method with broad spectrum of application in the preparation of self‐organizing amphiphilic copolymers having poly(glycerol monomethacrylate) (PG2MA) as a hydrophilic part is herein reported. The approach relies on the facile preparation of silylated glycerol monomethacrylate (G2MA‐TMS) monomer, and its controlled atom transfer radical polymerization (ATRP) in organic media, which produced well‐defined (co)polymers with predictable molar mass and low dispersity, followed by desilylation. The wide scope of such a strategy was demonstrated by the successful synthesis of original polycaprolactone‐b‐poly(glycerol monomethacrylate) (PCL‐b‐PG2MA) diblock copolymers with the ability to self‐assemble into ordered structures (micelles and vesicles) in an aqueous medium.

     

Interactions of amphiphilic block copolymers with lipid model membranes

Studies on interactions between amphiphilic block copolymers and lipid membranes have been focused traditionally on ABA triblock copolymers of poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide), widely due to their commercial availability. However, new architectures of amphiphilic block copolymer have been synthesized in recent years partially taking advantage of new polymerization techniques. This review focuses on amphiphilic block copolymers with potential biological activity and on model membrane systems used for studying interactions with such block copolymers. Experimental methods to study block copolymer–phospholipid interactions in Langmuir monolayers, liposomes, and planar bilayers are summarized. This work is intended to convey a better understanding of amphiphilic block copolymers used for in vitro and in vivo experiments in medicine and pharmacy. Recent developments and open questions are addressed.     

Sequential synthesis of multiblock copolymers by atom transfer radical and cationic polymerization

ABCBA‐type pentablock copolymers of methyl methacrylate (MMA), styrene (S), and isobutylene (IB) were prepared by a three‐step synthesis, which included atom transfer radical polymerization (ATRP) and cationic polymerization: (1) poly(methyl methacrylate) (PMMA) with terminal chlorine atoms was prepared by ATRP initiated with an aromatic difunctional initiator bearing two trichloromethyl groups under CuCl/2,2′‐bipyridine catalysis; (2) PMMA with the same catalyst was used for ATRP of styrene, which produced a poly(S‐b‐MMA‐b‐S) triblock copolymer; and (3) IB was polymerized cationically in the presence of the aforementioned triblock copolymer and BCl₃, and this produced a poly(IB‐b‐S‐b‐MMA‐b‐S‐b‐IB) pentablock copolymer. The reaction temperature, varied from ?78 to ?25 °C, significantly affected the IB content in the product; the highest was obtained at ?25 °C. The formation of a pentablock copolymer with a narrow molecular weight distribution provided direct evidence of the presence of active chlorine at the ends of the poly(S‐b‐MMA‐b‐S) triblock copolymer, capable of the initiation of the cationic polymerization of IB in the presence of BCl₃. A differential scanning calorimetry trace of the pentablock copolymer (20.1 mol % IB) showed the glass‐transition temperatures of three segregated domains, that is, polyisobutylene (?87.4 °C), polystyrene (95.6 °C), and PMMA (103.7 °C) blocks. One glass‐transition temperature (104.5 °C) was observed for the aforementioned triblock copolymer. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 6098–6108, 2004     

Self-assembled polypeptide-block-poly(vinylpyrrolidone) as prospective drug-delivery systems

Poly(β-benzyl-l-aspartate)-block-poly(vinylpyrrolidone) diblock copolymers (PAsp(OBzl)-b-PVP) having both hydrophobic and hydrophilic segments of various lengths were synthesized by a combination of ATRP and ROP. These amphiphilic diblock copolymers formed polymeric micelles consisting of a hydrophobic PAsp(OBzl) core and a hydrophilic PVP shell in aqueous solution. The block copolymer was characterized using ¹H NMR and gel permeation chromatography (GPC) analysis. Due to its core–shell structure, this block polymer forms unimolecular micelles in aqueous solutions. The micelle properties of PAsp(OBzl)-b-PVP diblock copolymer were extensively studied by dynamic light scattering (DLS), fluorescence spectroscopy, and transmission electron microscopy (TEM). PAsp(OBzl)-b-PVP copolymers displayed the lowest CMC and demonstrated little cytotoxicity when exposed to SW-1990 pancreatic cancer cells. In order to assess its application in biomedical area, the anti-inflammation drug prednisone acetate was loaded as the model drug in the polymeric nanoparticles. In vitro release behavior of prednisone acetate was investigated, which showed a dramatic responsive fast/slow switching behavior according to the pH-responsive structural changes of a micelle core structure. All of theses features are quite feasible for utilizing it as a novel intelligent drug-delivery system.     

Synthesis of Poly(methyl methacrylate)-poly(poly(ethylene glycol) methacrylate)-polyisobutylene ABCBA Pentablock Copolymers by Combining Quasiliving Carbocationic and Atom Transfer Radical Polymerizations and Characterization Thereof

Novel, unique amphiphilic pentablock terpolymers consisting of the highly hydrophobic polyisobutylene (PIB) mid-segment attached to the hydrophilic combshaped poly(poly(ethylene glycol) methacrylate) (PPEGMA) polymacromonomer chains, which are coupled to poly(methyl methacrylate) (PMMA) outer segments were synthesized by the combination of quasiliving carbocationic polymerization and atom transfer radical polymerization (ATRP). First, a bifunctional PIB macroinitiator was prepared by quasiliving carbocationic polymerization and subsequent quantitative chain end derivatizations. Quasiliving ATRP of PEGMAs with different molecular weights (M_n = 188, 300 and 475 g/mol) led to triblock copolymers which were further reacted with MMA under ATRP conditions to obtain PMMA-PPEGMA-PIB-PPEGMA-PMMA ABCBA-type pentablock copolymers. It was found that slow initiation takes place between the PIB macroinitiator and PEGMA macromonomers with higher molecular weights via ATRP. ATRP of MMA with the resulting block copolymers composed of PIB and PPEGMA chain segments led to the desired block copolymers with high initiating efficiency. Investigations of the resulting pentablock copolymers by DSC, SAXS and phase mode AFM revealed that nanophase separation occurs in these new macromolecular structures with average domain distances of 11-14 nm, and local lamellar self-assembly takes place in the pentablocks with PPEGMA polymacromonomer segments of PEGMAs with M_n of 118 g/mol and 300 g/mol, while disordered nanophases are observed in the block copolymer with PEGMA having molecular weight of 475 g/mol. These new amphiphilic block copolymers composed of biocompatible chain segments can find applications in a variety of advanced fields.     

Studies on the self-assembly behavior of the amphiphilic block copolymer of PSt-b-PAA in apolar solvents with polar fluorescent probe

The block copolymer of polystyrene-b-poly(butyl acrylate) (PSt-b-PBA) with a well-defined structure was synthesized by atom transfer radical polymerization (ATRP); its structure was characterized, and the living polymerization was also validated by gel permeation chromatography, Fourier transform infrared, and ¹H NMR measurements. Then, the amphiphilic block copolymer of polystyrene-b-poly(acrylic acid) (PSt-b-PAA) has been prepared by hydrolysis of PSt-b-PBA, and copolymers of PSt-b-PAA with longer PSt blocks and shorter PAA blocks were obtained by controlling the conditions of ATRP polymerization. The reversed micelle solution of PSt-b-PAA in toluene was prepared by using the single-solvent dissolving method, and the reverse micellization behavior of PSt-b-PAA in toluene was mainly investigated in this paper. The fluorescent probe technique was used by using polar fluorescence compound N-(1-Naphthyl)ethylenediamine dihydrochloride (NEAH) as a polar fluorescent probe to study the reverse micellization behavior of PSt-b-PAA. It was found that the reverse micellization behaviors of PSt-b-PAA in toluene can be clearly revealed by using NEAH as a polar fluorescence probe, and the critical micelle concentrations (cmcs) can be well displayed. The experimental results showed that the self-assembling behavior of PSt-b-PAA in toluene depends apparently on the microstructure of the macromolecules and is also influenced by the temperature. For the copolymers of PSt-b-PAA with the same length of hydrophobic PSt blocks, the copolymer with a longer hydrophilic block PAA has lower cmc, and at higher temperature, the copolymer has lower cmc.     

Novel Amphiphilic Poly(N-vinylpyrrolidone) Block Copolymer: Aggregative Behavior and Interaction with DNA

Summary: Novel block copolymers poly(N-vinylpyrrolidone)-block-poly[(tert-butoxy) carbonyl] tryptophanamido-N′-methacryl thiourea (PVP-b-PTAM-I, II and III) were synthesized by atom transfer radical polymerization (ATRP) in DMF using PVP-Cl as macroinitiator. The structures of the copolymers were characterized by UV-vis and GPC-MALLS. The results revealed that the copolymers with controlled molecular weight and relatively low polydispersity (PDI < 1.34) were obtained through ATRP. By means of dynamic light scattering (DLS) and transmission electron microscopy (TEM), we demonstrated that copolymer PVP-b-PTAM self-aggregated to form spherical micelles in aqueous solution and the size of the micelles increased with increasing hydrophobic contents. The interaction of PVP-b-PTAM with DNA was explored using ethidium bromide (EB) quenching experiments. The interaction between PVP-b-PTAM and DNA markedly depended on both the copolymer concentration and composition. The PVP-b-PTAM-II and III with higher hydrophobic contents exhibited highly complexed DNA ability at low copolymer concentration, such as 0.017 mg/mL, relative to PVP-b-PTAM-I. As the copolymer concentration further increased for PVP-b-PTAM-II and III, they first exhibited a sharply decreased affinity for DNA and then kept steady. The interaction mechanism between the amphiphilic copolymers and the EB-DNA complex was discussed in detail.     

Synthesis of stimulus-responsive block copolymer gelators by atom transfer radical polymerisation

The synthesis of new stimulus-responsive block copolymer gelators using atom transfer radical polymerisation (ATRP) in either methanol or 2-propanol/water mixtures at 20 °C is described. Bifunctional and trifunctional initiators were used to prepare ABA triblock and I(BA)₃ three-arm star diblock copolymers, respectively, using a ‘one-pot’ ATRP protocol, in which the central block comprised poly(glycerol monomethacrylate) and the outer blocks comprised pH-responsive poly[2-(diethylamino)ethyl methacrylate] or poly[2-(diisopropylamino)ethyl methacrylate]. These copolymers dissolve molecularly in acidic solution but formed free-standing gels at around neutral pH on addition of base. Gel strength was judged by both tube inversion experiments and shear rheometry measurements and a comparison between the linear and star architectures was made.     

Formation of genus vesicles in dilute aqueous solution by PtBAx-b-PS130-b-PEO90-b-PS130-b-PtBAx amphiphilic pentablock terpolymers

A series of linear symmetrical ABCBA pentablock terpolymers, poly(tert-butyl acrylate)-b-polystyrene-b-poly(ethylene oxide)-b-polystyrene-b-poly(tert-butyl acrylate) with constant lengths of PS and PEO blocks but different degree of polymerization x of PtBA block, namely PtBA_x-b-PS₁₃₀-b-PEO₉₀-b-PS₁₃₀-b-PtBA_x (x = 40, 75, 100, 165, and 200), were found to form various vesicular nanostructures in dilute aqueous solution as observed by conventional transition electron microscopy (TEM), cryogenic transmission electron microscopy (cryo-TEM) and scanning electron microscopy (SEM). Genus vesicles with nanometer sizes and various genus values (g), including individual spherical vesicles, tubular vesicles (g = 0), toroidal vesicles (g = 1) and the vesicles with even larger g values (g > 1) were observed, respectively. The g value of genus vesicles formed by PtBA_x-b-PS₁₃₀-b-PEO₉₀-b-PS₁₃₀-b-PtBA_x pentablock terpolymers decreased with the increasing length of PtBA block. The formation mechanism of genus vesicles was preliminarily discussed by the combination of membrane bending energy, the area-difference-elasticity and the edge effect.