Syntheses of amphiphilic block copolymers. Block copolymers of methacrylic acid and p-N,N-dimethylaminostyrene

Amphiphilic block copolymers consisting of methacrylic acid (MA) sequences and p-N,N-dimethylaminostyrene (DMS) sequences were prepared by living anionic polymerization. DMS was polymerized by lithium naphthalene in tetrahydrofuran to yield a living polymer solution, to which trimethylsilyl methacrylate (TMSM) was added to allow the block copolymerization. The conversion of TMSM was dependent on the countercation, i.e., with Na⁺ as counterion, no quantitative conversion was reached owing to premature termination, whereas with Li⁺ the conversion was quantitative. The role of the counterion was discussed in some detail in connection with self-termination by the backbiting mechanism. The trimethylsilyl ester groups in the block copolymer were quantitatively hydrolyzed by treatment with aqueous methanol at room temperature, yielding MA sequences. The block copolymer of MA and DMS exhibited micellar properties in an aqueous solution.     

Amphiphilic block copolymer of 9-vinylphenanthrene and methacrylic acid: Fluorescence quenching of phenanthrene residue in aqueous medium

Amphiphilic block copolymers of 9-vinylphenanthrene (VPh) and methacrylic acid (MA) were prepared by a two-step living anionic polymerization of VPh and trimethylsilyl methacrylate followed by hydrolysis of the trimethylsilyl ester groups. Bis(2-hydroxyethyl) terephthalate, an oxidative quenching agent with amphiphilic nature, strongly quenched the fluorescence of phenanthrene groups in the block copolymer in aquecus solution. Apparent second-order rate constants k_q for the quenching ranged in the magnitude of 10¹¹?10¹²M^?1 s^?1 in the borate (pH 9) and phosphate (pH 7) buffers, whereas those in DMF solution were found to be ～10⁹M^?1 s^?1. No such difference in k_q for the aqueous and DMF solutions was observed with the related random copolymer. The results suggest that a considerable increase in the effective concentration of the quencher around the VPh sequences in the block copolymer resulted from hydrophobic association. Fumaric acid (FA), an anionic quencher, did not quench the fluorescence of the copolymer at pH 9 and 7, presumably because of the lack of accessibility of the quencher to the copolymer due to electrostatic repulsion. However, in neat water in which only a part of the carboxyl groups of MA sequences are dissociated and therefore the charge effect is minimized, FA quenched the fluorescence, with the k_q value approximating the diffusion control limit.     

Synthesis of new amphiphilic block copolymers. Block copolymer of sulfonated glycidyl methacrylate and alkyl methacrylate

Water-soluble amphiphilic block copolymers consisting of a hydrophobic block of poly(alkyl methacrylate) and a hydrophilic anionic polyelectrolyte block have been synthesized by a living anionic polymerization of methyl methacrylate and glycidyl methacrylate and subsequent selective modification of the oxirane groups of the glycidyl methacrylate block into hydroxysulfonate groups by a phase transfer catalyzed sulfonation reaction. The block copolymers were characterized by a predictable motecular weight and a narrow molecular weight distribution while the yield was quantitative. These amphiphilic block copolymers display surfaceactive behavior in water and they are characterized by a critical micelle concentration.     

Synthesis of polystyrene-poly(methacrylic acid) amphiphilic block copolymers by free-radical polymerization through chain-transfer and hydrosilylation reactions

Amphiphilic polystyrene-poly(methacrylic acid) block copolymers of various compositions have been synthesized by free-radical polymerization via chain-transfer and hydrosilylation reactions, as established by viscometry, IR spectroscopy, and fractionation measurements. The compositional homogeneity of the block copolymers worsens with an increase in the content of a low-molecular-mass monomer in the starting mixture and is independent of the nature of the terminal unit of a macromonomer.     

Organoboronium amphiphilic block copolymers

A new class of amphiphilic organometallic block copolymers with cationic organoboron pendant groups was developed. Selective replacement of one of the bromine substitutents on each boryl group of the block copolymer PSBBr₂‐b‐PS with an organometallic reagent ArM (ArM = 2,4,6‐trimethylphenyl copper, 4‐t‐butylphenyltrimethyl tin) followed by treatment with 2,2′‐bipyridine gave the novel block copolymers [ 3Ar ](Br)_n as light yellow solid materials that show good stability in air and moisture and high solubility in most organic solvents. Their structure and composition were confirmed by multinuclear NMR, GPC, and elemental analysis. Highly regular micellar aggregates form in block‐selective solvents (e.g., MeOH, toluene) as demonstrated by ¹H NMR, dynamic light scattering, and transmission electron microscopy. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 6612–6618, 2009     

Block copolymers derived from azobiscyanopentanoic acid. IV. Synthesis of a polyamide–polystyrene block copolymer

Polyamides 6.10 and 6.6 (PA^* 6.10 and 6.6) containing small amounts of ? N?N? units in the main chains were prepared by interfacial polycondensation between hexamethylenediamine and sebacoyl chloride or adipoyl chloride with addition of azobiscyanopentanoyl chloride. Polyamide–polystyrene block copolymers (PA-b-PSt) were then prepared by decomposition of the ? N?N? units of PA^*, initiating radical polymerization of styrene in m-cresol. The average PA block length of PA-b-PSt thus formed was longer than that expected from the initially present PA segments between the ? N?N? units. This is probably due to recombination of PA radicals whose initiation efficiency is as low as 15%. The PSt blocks also had higher molecular weight (7000–79,000) in comparison with homopolystyrene produced from monomeric azobiscyanopentanoic acid used as an initiator due to higher viscosity of polymerization system. Variation of intrinsic viscosity and turbidimetric titration behavior along with the change in composition were also discussed.     

Block copolymers derived from azobiscyanopentanoic acid. VI. Synthesis of a polyethyleneglycol–polystyrene block copolymer

Polycondensations were carried out between azobiscyanopentanoly chloride (ACPC) and polyethyleneglycols (PEG) having average molecular weight of 600, 2000, 8400, and 21,500, resulting in the chain extended PEG of several times the original polymer chain length and containing scissile ? N?N? units of azobiscyanopentanoic acid (ACPA). The poly(polyethyleneglycol-azobiscyanopentanoate), designated as \documentclass{article}\pagestyle{empty}\begin{document}$\rlap{--} (PEG\rlap{--} )_n^*$\end{document} were thermally decomposed in the presence of styrene (St) to obtain PEG–PSt block copolymers. The amount of St consumed was proportional to [? N?N? ]^0.5 and [St]^1.2, whereas the chain length of the PSt segment was proportional to [? N? N? ]^?0.5 and [St]^0.8.     

功能性两亲嵌段共聚物的研究进展

功能性两亲嵌段共聚物因自身独特的性质而在靶向输送、控制释放、分子识别等领域得到广泛的应用.本文对这类嵌段共聚物的合成方法、其胶束的形成机理、制备形式、表征手段以及一些常见的具有光学活性的两亲嵌段共聚物及其应用进行了综述.     

Hydrophobic energy estimation for giant vesicle formation by amphiphilic poly(methacrylic acid)-block-poly(alkyl methacrylate-random-mathacrylic acid) random block copolymers

The self-assembly induced by the photocontrolled/living radical polymerization mediated by 4-methoxy-2,2,6,6-tetramethylpiperidine-1-oxyl was performed for amphiphilic poly(methacrylic acid)-block-poly(alkyl methacrylate-random-methacrylic acid) containing ethyl, n-propyl, and n-butyl methacrylates in order to control the morphology based on the hydrophobic-hydrophilic balance. The morphology transformation from films to spherical vesicles via the transition was well-controlled by adjusting the ratio of the alkyl methacrylate unit to the methacrylic acid in the hydrophobic random copolymer block. The copolymers formed the respective morphologies at different ratios dependent on the alkyl chain length of the methacrylates; the ratio for the formation of the respective morphologies decreased as the alkyl chain length increased. The hydrophobic energy estimation of these copolymers demonstrated that the respective morphologies had definite hydrophobic energies independent of the alkyl chain length, indicating that the morphologies were determined only by the hydrophobic magnitude of the random copolymer block.     

Composition-tunable properties of amphiphilic comb copolymers containing protected methacrylic acid groups for multicomponent protein patterning

Methods to micropattern multiple protein components on surfaces under mild conditions are of interest for biosensing, proteomics, and fundamental studies in cell biology. Here, we report on the composition-dependent thin-film solubility behavior of o-nitrobenzyl methacrylate (oNBMA, a protected form of methacrylic acid)/methyl methacrylate (MMA)/poly(ethylene glycol) methacrylate (PEGMA) random terpolymers, materials which are promising as aqueous-processible photoresists. Over a broad range of terpolymer compositions, these materials formed initially water-insoluble films, which, upon UV irradiation, rapidly dissolved in aqueous solutions above a critical pH. This threshold pH ranged from approximately 5-7 depending upon the copolymer composition and decreased as the relative ratio of MMA to PEGMA in the copolymers decreased. In addition, in a narrow window of compositions near 35:0:65 oNBMA/MMA/PEGMA (wt ratio), an inverse behavior was observed: thin films that were initially water soluble became kinetically stable in aqueous solutions after UV exposure. The time for these films to completely dissolve was hours rather than seconds, and the rate of dissolution was both temperature- and pH-dependent. This behavior is consistent with a transient stability imparted by inter- and intramolecular hydrogen bonding in the film. Using copolymers of this composition as negative tone photoresists, we demonstrated patterning of two proteins into two discrete regions of a surface. The selective solubility of the resist copolymer allows the entire patterning process to be completed using only biological buffers as solvents and across a temperature range between 4 and 37 degrees C without subjecting either protein to ultraviolet irradiation or dehydration. These materials are thus of interest for complex surface photopatterning under mild aqueous conditions.     

新型线状-树枝状两亲嵌段共聚物的合成

本文设计合成了一系列由不同链长的聚丙烯酸(PAA)为亲水嵌段和不同代数聚苄醚树枝体(Dendr.PBE)为疏水嵌段的杂化共聚物(PAA-Dendr.PBE)。     

Synthesis of anionic amphiphilic carbosilane block copolymer: Poly(1,1‐diethylsilacyclobutane‐block‐methacrylic acid)

An amphiphilic block copolymer of silacyclobutane and methacrylic acid (MAA) was synthesized via a living anionic polymerization of 1,1‐diethylsilacylcobutane (EtSB). Sequential addition of 1,1‐diphenylethylene and t‐butyl methacrylate (tBMA) to living poly(EtSB) in the presence of lithium chloride gave poly(EtSB‐block‐tBMA) with narrow molecular weight distributions. The t‐butyl ester groups in the obtained polymer were readily hydrolyzed via heating in 1,4‐dioxane in the presence of concentrated aqueous hydrochloric acid. The block copolymer with a short MAA segment was soluble in chloroform and insoluble in methanol and basic water, whereas the block copolymer with a long MAA segment was soluble in methanol and basic water and insoluble in chloroform. The block polymer (EtSB/tBMA = 45/60) formed a monolayer film on the water surface; this was confirmed by surface pressure measurement. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 86–92, 2001     

Interaction of amphiphilic block copolymer micelles with surfactants

An out line and summary of literature studies on interactions between different types of amphiphilic copolymer micelles with surfactants has been given. This field of research is still emerging and it is difficult presently to make generalisations on the effects of surfactants on the copolymer association. The effects are found to be varied depending upon the nature and type of hydrophobic (hp) core and molecular architecture of the copolymers and the hydrocarbon chain length and head group of surfactants. The information available on limited studies shows that both anionic and cationic surfactants (in micellar or molecular form) equally interact strongly with the associated and unassociated forms of copolymers. The beginning of the interaction is typically displayed as critical aggregation concentration (CAC), which lies always below the critical micelle concentration of the respective surfactant. The surfactants first bind to the hydrophobic core of the copolymer micelles followed by their interaction with the hydrophilic (hl) corona parts. The extent of binding highly depends upon the nature, hydropobicity of the copolymer molecules, length of the hydrocarbon tail and nature of the head group of the surfactant. The micellization of poly(ethylene oxide) (PEO)–poly(propylene oxide) (PPO)–poly(ethylene oxide) was found to be suppressed by the added surfactants and at higher surfactant concentrations, the block copolymer micelles get completely demicellized. This effect was manifested itself in the melting of liquid crystalline phases in the high copolymer concentrations. However, no such destabilization was found for the micelles of polystyrene (PS)–poly(ethylene oxide) copolymers in water. On the contrary, the presence of micellar bound surfactant associates resulted in to large super micellar aggregates through induced intra micellar interactions. But with the change in the hydrophobic part from polystyrene to poly(butadiene) (PB) in the copolymer, the added surfactants not only reduced the micellar size but also transformed cylindrical micelles to spherical ones. The mixtures in general exhibited synergistic effects. So varied association responses were noted in the mixed solutions of surfactants and copolymers.     

Synthesis and surface properties of amphiphilic block copolymers polyvinylpyrrolidone-block-polystyrene

Amphiphilic block copolymers of N-pyrrolidone and styrene were prepared by chain transfer to organogermanium compounds bis(pentafluorophenyl)germane and tris(pentafluorophenyl)germane. The relative chain-transfer constants were determined. The surface properties of the isolated block copolymers with various numbers of units in the hydrophilic block were studied. The polar and dispersive components of the surface tension of films of the amphiphilic block copolymers were calculated by the Zisman method.     

Polymerization of cyclic acetals. II. Synthesis of amphiphilic block copolymers

The sequential copolymerization of 1,3,6-trioxacyclooctane (TOC) and 1,3-dioxolane (DOL) (B) with various vinyl monomers (A) was investigated. Under appropriate conditions amphiphilic block copolymers of the type AB and ABA were formed. The reaction mixtures and the isolated polymers were analyzed by GPC (double detection—IR and UV at 254 nm), IR, ¹H-, and ¹³C-NMR spectroscopy. Block copolymers with chosen molecular weights and low polydispersity could be obtained only by sequential copolymerization of p-methoxystyrene on “living” TOC. In the polymerization of DOL with α-methylstyrene and i-butyl vinyl ether (IBVE) transfer reactions take place to a larger degree.     

Synthesis and aggregation behaviour of amphiphilic block copolymers with random middle block

The effect of microstructure on the aggregation behaviour of symmetrical di- and triblock copolymers P(BMA)-b-P(MAA) and P(BMA)-b-P(BMA-co-MAA)-b-P(MAA) with a molecular weight of 40,000 g/mol was studied. The critical micelle concentration, hydrodynamic radius and morphology of the micelles were determined by fluorescence spectroscopy, dynamic light scattering and scanning force microscopy (SFM). Whereas no effect of the microstructure on the critical micelle concentration could be detected, the hydrodynamic radius decreased from di- to triblock copolymer from 53 to 36 nm. The decrease of about 32% corresponds to the length of the random middle block within the triblock copolymer so that the reduction in hydrodynamic radius was caused by a complete orientation of the random middle block at the core corona interface. Finally, the SFM investigation showed that dehydration of micelles on a substrate is accompanied by formation of a physisorbed monolayer with a thickness of 2 nm on which the micelles are deposited.     

Non-ionic amphiphilic block copolymers by RAFT-polymerization and their self-organization

Water-soluble, amphiphilic diblock copolymers were synthesized by reversible addition fragmentation chain transfer polymerization. They consist of poly(butyl acrylate) as hydrophobic block with a low glass transition temperature and three different nonionic water-soluble blocks, namely, the classical hydrophilic block poly(dimethylacrylamide), the strongly hydrophilic poly(acryloyloxyethyl methylsulfoxide), and the thermally sensitive poly(N-acryloylpyrrolidine). Aqueous micellar solutions of the block copolymers were prepared and characterized by static and dynamic light scattering analysis (DLS and SLS). No critical micelle concentration could be detected. The micellization was thermodynamically favored, although kinetically slow, exhibiting a marked dependence on the preparation conditions. The polymers formed micelles with a hydrodynamic diameter from 20 to 100 nm, which were stable upon dilution. The micellar size was correlated with the composition of the block copolymers and their overall molar mass. The micelles formed with the two most hydrophilic blocks were particularly stable upon temperature cycles, whereas the thermally sensitive poly(N-acryloylpyrrolidine) block showed a temperature-induced precipitation. According to combined SLS and DLS analysis, the micelles exhibited an elongated shape such as rods or worms. It should be noted that the block copolymers with the most hydrophilic poly(sulfoxide) block formed inverse micelles in certain organic solvents.     

Synthesizing amphiphilic block copolymers through macromolecular azo-coupling reaction

This communication reports a new approach to synthesize amphiphilic block copolymers. The copolymers with well-defined structures were synthesized by macromolecular azo-coupling reaction between the diazonium salt of aniline-functionalized PEG and the polymeric blocks with a terminal suitable for the azo-coupling reaction.