Novel fluorescent amphiphilic block copolymers: Controllable morphologies and size by self-assembly

New fluorescent amphiphilic copolymers polyacrylamide-b-poly(p-methacrylamido)acetophenone thiosemicarbazone (PAM-b-PMATC) were synthesized by atom transfer radical polymerization (ATRP) method. The structures of polymers were confirmed by ¹H NMR and gel permeation chromatography-multi-angle laser light scatting (GPC-MALLS). PAM-b-PMATC showed a broad emission peak about 388 nm excited at 318 nm in aqueous solution. The self-assembly behavior of PAM-b-PMATC in the binary mixture formamide/water was observed by transmission electron microscope (TEM). It indicated that PAM-b-PMATC-I and -II with the same PAM block self-assembled to vesicles and sunflower-like micelles. The water fraction in the mixture could control the size and thickness of vesicles. Vesicle size increased from 50 to 420 nm and vesicle thickness changed from 5 to 50 nm with water content ranging from 33 to 90 vol.%. In addition, the cytotoxicity in vitro of PAM-b-PMATC-I and its nanoparticles loaded with methotrexate (MTX) were evaluated by MTT assay.     

The amphiphilic multiarm copolymers based on hyperbranched polyester and lysine: Synthesis and self-assembly

The amphiphilic multiarm copolymers were synthesized through the modification of commercially available hyperbranched polyesters(Boltorn H40) with N-ε-carbobenzoxy-L-Lysine N-carboxyanhydride(ZLys-NCA).After being condensed with N-Boc-phenylalanine(Boc-~NPhe) and deprotected the Boc-groups in trifluoroacetic acid(TFA),the original terminal hydroxyl groups were transformed into the amino groups and then initiated the ring-opening polymerization of ZLys-NCA.The hydrophilic poly(L-lysine) was grafted to the surface of Boltorn H40 successfully after the protecting benzyl groups were removed by the HBr solution in glacial acetic acid(33 wt%).The resulting multiarm copolymers were characterized by the ~1H-NMR,GPC and FTIR.The arm length calculated by NMR and GPC analysis was about 3 and 13 lysine-units for H40-Phe-PLysl and H40-Phe-PLys2 respectively.Due to the amphiphilic molecular structure,they displayed ability to self-assemble into spherical micelles in aqueous solution with the average diameter in the range from 70 nm to 250 nm.The CMC of H40-Phe-PLysl and H40-Phe-PLys2 was 0.013 mg/mL and 0.028 mg/mL,respectively, indicating that H40-Phe-PLysl with shorter arm length is easier to self-assemble than H40-Phe-PLys2 with longer arm length.     

Synthesis, characterization and self-assembly of ion-bonded amphiphilic A2B miktoarm star copolymers containing an azobenzene unit at the core

An azobenzene-containing supramolecular copolymers, consisted of two polystyrene (PSt) arms and one poly(ethylene oxide) (PEO) arm linked via ionic bond, has been designed and successfully synthesized. Monomethoxy PEO with phenylazobenzenesulfonic acid as the terminus (PEO-NN-SO₃H) was utilized to react with polystyrene carrying tertiary amino group at the middle of the polymer chain (PSt₂-N(CH₃)₂) to form ion-bonded supramolecular star copolymers (PSt₂-NN-PEO) with an azobenzene group at the core based on the interaction between sulfonic acid group and amino group. The obtained copolymers were characterized by ¹H nuclear magnetic resonance (¹H NMR) and gel permeation chromatography (GPC) techniques. The self-assembly behavior of the copolymers with different molecular weight of PSt was investigated, which shows solid spherical aggregates in water. The aggregation leads to the lower isomerization degree (54%) at the photostationary state in water compared with that in 1,4-dioxane (82%).     

侧基带有L-苯丙氨酸的手性两亲嵌段共聚物的合成及其自组装行为

N3-苯丙氨酸与嵌段共聚物聚乙二醇-b-聚炔丙基缩水甘油(MPEO-b-PGPE)发生click反应,合成了具有光学活性的两亲嵌段共聚物聚乙二醇-B-聚L-苯丙氨酸三唑基缩水甘油(MPEO-b-PGTP),用1H-NMR和元素分析对其结构和组成进行表征.并对其自组装行为进行研究,滴体积法测定MPEO-b-PGTP溶...     

Amphiphilic block copolymers by a combination of anionic polymerization and selective post-polymerization functionalization

Anionic polymerization is the oldest known living/controlled polymerization methodology that leads to well defined macromolecules. It has been also used, with considerable success, for the synthesis of amphiphilic block copolymers (AmBC), a class of functional copolymers having interesting self-assembling properties and high potential for applications in various technological fields. The use of mild and effective post-polymerization functionalization/chemical modification reactions on block copolymers has substantially increased the synthetic capabilities of anionic polymerization methodologies, toward the creation of a variety of AmBC. In this feature article we review work done on these directions in the last ten years. Some perspectives and future work on this particular field of polymer science are also discussed.     

An amphiphilic supramolecular polymer: Construction,self-assembly and pH-responsive behavior in water

A novel amphiphilic supramolecular polymer (ASP) with rigid linear main chain has been constructed by the co-assembly of a rigid amphiphilic monomer and cucurbit[8]uril (CB[8]) in water, driven by CB[8]-based host-guest interactions. The ASP could further self-assemble into well-defined architectures including nanotubes and 2D films, depending on its concentration. Moreover, pH-responsive behavior of the ASP was also observed.     

Zinc ion induced polymorphism in macromolecular self-assembly of diblock copolymers

A novel interconnected cylindrical micellar network was prepared from a diblock copolymer, poly(maleic anhydride-alt-styrene)-b-polystyrene, in ethanol under a self-assembly directing agent: Zn²⁺ ions. The solution containing interconnected cylindrical network is bluish and transparent, which is stable for more than 6 months at room conditions without any observable macroscopic phase separation. In aqueous solution, however, hydrolysis of the anhydride yields hydrophilic carboxyl groups, which result in formation of uniform positive spherical micelles from the same diblock polymer. The nanostructures of both the spherical micelles and cylindrical assemblies are characterized with light scattering and transmission electron microscopy (TEM).     

The directed self-assembly of amphiphilic diblock copolymers in selective solvents

The directed self-assembly of diblock copolymers in solvents is studied systematically using a simulated annealing method. Effects of the shape, scale, and adsorption capacity of the induced surface on the morphology of the aggregates are examined. A variety of morphologies are predicted. By increasing the scale of induced surface, the micellar shape transforms from cylinder to sheet with a tail and finally to thin sheet without tail. The shape of induced surface determines the sheet’s shape, such as rounded and square. Configurations of hydrophobic blocks and interfacial energies are investigated by calculating the mean square end-to-end distances and the contact numbers between hydrophobic monomer and other species, respectively.     

Synthesis and surface characterization of an amphiphilic fluorinated copolymer via emulsifier-free emulsion polymerization of RAFT

The hydrophobic monomer dodecafluoroheptyl methacrylate has been copolymerized with hydrophilic monomer methacrylic acid in aqueous solution without any additional emulsifier used via a two-step polymerization process of RAFT. The FTIR and GPC results indicated that amphiphilic copolymers with a narrow molecular weight distribution and well-defined blocks have been synthesized successfully. And the copolymers are likely to form steady micelles in the emulsion. Indicated by TEM, it is clear that micelles with a diameter of 70-120 nm have been formed. Despite a content of 22 wt% of hydrophilic carboxyl, films formed by casting the emulsion onto the baseplate can be hydrophobic after heating treatment.     

Synthesis and characterization of amphiphilic triblock polymers by copper mediated living radical polymerization

2-Dimethylaminoethyl methacrylate (DMAEMA) and 2-diethylaminoethyl methacrylate (DEAEMA) block copolymers have been synthesized by using poly(ethylene glycol), poly(tetrahydrofuran) (PTHF) and poly(ethylene butylenes) macroinitiators with copper mediated living radical polymerization. The use of difunctional macroinitiator gave ABA block copolymers with narrow polydispersities (PDI) and controlled number average molecular weights (M_n’s). By using DMAEMA, polymerizations proceed with excellent first order kinetics indicative of well-controlled living polymerization. Online ¹H NMR monitoring has been used to investigate the polymerization of DEAEMA. The first order kinetic plots for the polymerization of DEAMA showed two different rate regimes ascribed to an induction period which is not observed for DMAEMA. ABA triblock copolymers with DMAEMA as the A blocks and PTHF or PBD as B blocks leads to amphiphilic block copolymers with M_n’s between 22 and 24 K (PDI 1.24-1.32) which form aggregates/micelles in solution. The critical aggregation concentrations, as determined by pyrene fluorimetry, are 0.07 and 0.03 g dm⁻¹ for PTHF- and PBD-containing triblocks respectively.     

Organized polymerization of functional diblock copolymers possessing central isoprene groups

Functional diblock copolymers possessing central isoprene groups were synthesized by anionic addition in a three-stage process using styrene, isoprene, and 2-vinylpyridine monomers. These diblock copolymers formed microphase-separated structure in the solid state. Where the central isoprene groups are organized regularly at the domain interface of the microphase-separated structure, this is due to the functional groups being located at the block junction position. Addition-condensation of diblock copolymer film with sulfur monochloride formed A_nB_n star block copolymers by organization effects. © 1993 John Wiley & Sons, Inc.     

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.     

Synthesis of azobenzene‐containing polymers via RAFT polymerization and investigation on intense fluorescence from aggregates of azobenzene‐containing amphiphilic diblock copolymers

The well‐defined azobenzene‐containing homopolymers, poly{6‐(4‐phenylazophenoxy)hexyl methacrylate (AHMA)} (PAHMA), were synthesized via reversible addition fragmentation chain transfer polymerization (RAFT) in anisole solution using 2‐cyanoprop‐2‐yl 1‐dithionaphthalate (CPDN) as the RAFT agent and 2,2′‐azobisisobutyronitrile (AIBN) as the initiator. The first‐order kinetic plot of the polymerization and the linear dependence of molecular weights of the homopolymers with the relatively low polydispersity index values (PDIs ≤ 1.25) on the monomer conversions were observed. Furthermore, the amphiphilic diblock copolymer, poly{6‐(4‐phenylazophenoxy)hexyl methacrylate (AHMA)}‐b‐poly{2‐(dimethylamino)ethyl methacrylate (DMAEMA)} (PAHMA‐b‐PDMAEMA), was prepared with the obtained PAHMA as the macro‐RAFT agent. The structures and properties of the polymers were characterized by ¹H NMR and GPC, respectively. Interestingly, the amphiphilic diblock copolymers in chloroform (CHCl₃) solution (PAHMA₂₃‐b‐PDMAEMA₉₇ (4 × 10^?5 M, M_n(GPC) = 18,400 g/mol, PDI = 1.48) and PAHMA₂₈‐b‐PDMAEMA₁₁₇ (6 × 10^?5 M, M_n(GPC) = 19,300 g/mol, PDI = 1.51) exhibited the intense fluorescence emission at ambient temperature. Moreover, the fluorescent intensity of PAHMA‐b‐PDMAEMA in CHCl₃ was sensitive to the ultraviolet irradiation at 365 nm, which increased within the first 10 min and later decreased when irradiation time was prolonged to 30 min or longer. The well distributed, self‐assembled micelles composed of azobenzene‐containing amphiphilic diblock copolymers, (PAHMA‐b‐QPDMAEMA)s (QPDMAEMA is quaternized PDMAEMA), in the mixed N,N‐dimethyl formamide (DMF)/H₂O solutions were prepared. Their fluorescent intensities decreased with the increasing amount of water. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5652–5662, 2008     

Synthesis and characterization of H-type amphiphilic liquid crystalline block copolymers by ATRP

H-type amphiphilic liquid crystalline block copolymers containing azobenzene were synthesized by atom transfer radical polymerization （ATRP）. Macroinitiators prepared by the esterification between poly（ethylene oxide） （PEG） and 2,2-dichloroacetyl chloride were utilized to initiate the polymerization of 6-[4-（4-ethoxyphenylazo）phenoxy]hexyl rnethacrylate （M6C）. The resulting macroinitiators and block copolymers were characterized by ^1H NMR, gel permeation chromatography （GPC）. Polarizing optical microscopy （POM） and differential scanning calorimetry （DSC） preliminarily revealed the liquid crystalline property of these block copolymers. This series of liquid crystalline block copolymers are promising in some areas, such as optical data storage, optical switch, and molecular devices.     

Synthesis and characterization of random or gradient butadiene-p-methylstyrene copolymers via anionic polymerization

Copolymers of 1,3-butadiene and p-methylstyrene （p-MS） were synthesized via anionic polymerization. A benzophenone-potassium complex was added to tune the reactivity ratio of the two monomers, leading to random and gradient composition alonglthe copolymer chain. The overall composition and microstructure could be controlled and well characterized by GPC and H-NMR. The p-MS was distributed from gradient to random with increasing the content of the benzophenone-potassium complex, and the 1,2-microstrucmre in the polybutadiene sequence increased at the same time. The hydrogenation of the copolymer of 1,3-butadiene and p-MS resulted in the corresponding saturated copolymer with well- defined structure and narrow molecular weight distribution.     

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.     

Miniemulsion polymerization of styrene using well-defined cationic amphiphilic comblike copolymers as the sole stabilizer

Well-defined, positively charged, amphiphilic copolymers containing long alkyl side chains were used as stabilizers in the miniemulsion polymerization of styrene. The copolymers were prepared by controlled free-radical copolymerization of styrene and vinyl benzyl chloride using either the reversible addition-fragmentation chain transfer method or TEMPO-mediated polymerization. The benzyl chloride moities were modified by two different long alkyl chain tertiary amines (N,N-dimethyldodecyl amine and N,N-dimethylhexadecyl amine) to yield the amphiphilic copolymers with vinylbenzyl dimethyl alkyl ammonium chloride units. Owing to their high structural quality, only a small amount of these copolymers was required to stabilize the latex particles (0.5–2 wt% vs styrene). Moreover, in the absence of any hydrophobic agent, the amphiphilic comblike copolymer preserved the colloidal stability of both the initial liquid miniemulsion and the final latex. Ill-defined, analogous copolymers were synthesized by conventional free-radical polymerization and in comparison, exhibited poor stabilization properties.     

Synthesis of amphiphilic block copolymers via ring opening polymerization and reversible addition-fragmentation chain transfer polymerization

Amphiphilic block copolymers were synthesized via a dual initiator chain transfer agent (inifer) that successfully initiated the ring opening polymerization (ROP) of l -lactide (LLA) and subsequently mediated the reversible addition-fragmentation chain transfer (RAFT) polymerization of poly(ethylene glycol) ethyl ether methacrylate (PEGEEMA). The formation of each polymer block was confirmed using ¹H nuclear magnetic resonance spectroscopy, as well as gel permeation chromatography, and comprehensive kinetics studies provide valuable insights into the factors influencing the synthesis of well-defined block copolymers. The effect of monomer concentration, reaction time, and molar ratios of inifer to catalyst on the ROP of LLA are discussed, as well as the ability to produce poly(lactide) blocks of different molecular weights. The synthesis of hydrophilic PPEGEEMA blocks was also monitored via kinetics to provide a better understanding of the role the chain transfer agent plays in facilitating the complex and sterically demanding RAFT polymerization of PEGEEMA.     

Synthesis and properties of polydimethylsiloxane-containing block copolymers via living radical polymerization

Polydimethylsiloxane (PDMS) block copolymers were synthesized by using PDMS macroinitiators with copper-mediated living radical polymerization. Diamino PDMS led to initiators that gave ABA block copolymers, but there was low initiator efficiency and molecular weights are somewhat uncontrolled. The use of mono- and difunctional carbinol–hydroxyl functional initiators led to AB and ABA block copolymers with narrow polydispersity indices (PDIs) and controlled number-average molecular weights (M_n's). Polymerization with methyl methacrylate (MMA) and 2-dimethylaminoethyl methacrylate (DMAEMA) was discovered with a range of molecular weights produced. Polymerizations proceeded with excellent first-order kinetics indicative of living polymerization. ABA block copolymers with MMA were prepared with between 28 and 84 wt % poly(methyl methacrylate) with M_n's between 7.6 and 35 K (PDI <1.30), which show thermal transitions characteristic of block copolymers. ABA block copolymers with DMAEMA led to amphiphilic block copolymers with M_n's between 9.5 and 45.7 K (PDIs of 1.25–1.70), which formed aggregates in solution with a critical micelle concentration of 0.1 g dm⁻³ as determined by pyrene fluorimetry experiments. Monocarbinol functional PDMS gave AB block copolymers with both MMA and DMAEMA. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 1833–1842, 2001