Thermal expansion of liquid crystalline amphiphilic di-block copolymer observed by simultaneous DSC-XRD

Phase transition process of PEO_m-b-PMA(Az)_n was investigated by the simultaneous DSC-XRD measurement using the synchrotron radiation facility. Four endothermic DSC peaks were observed during heating process. These DSC peaks were assigned to the melting of PEO, the transition from SmX, which is a mixture of super-cooled SmC and crystal, to SmC, from SmC to SmA, and from SmA to isotropic liquid state as determined by XRD profiles. In SmC phase, the liner expansion coefficient calculated from the spacing variation of the smectic layer distance was larger than that of the other phases. This result reflected the fact azobenzene moieties in the long-side chains of PMA(Az)_n forming the smectic layers and then they were tilted and stood up during the heating process.     

Mixing state of amphiphilic di-block copolymer/homopolymer blends

Summary The mixing state of amphiphilic di-block copolymers consisted of poly(ethylene oxide) and poly(methacrylate) having azobenzene moieties in the side chains p(EO)₁₁₄pMA(Az)₂₄ and poly(ethylene oxide) p(EO)₁₁₄ was investigated from the viewpoints of isothermal crystallization and nano-scale ordered structure. The chemical potential, which required establishing the constant crystal growth rate, decreased with the p(EO) content up to 60%. The hexagonal packed cylinder structure was observed for the blends with the p(EO) content up to 60% and the lattice spacing of (100) and (110) planes increased with the p(EO) content up to 60%. The blends of amphiphilic p(EO)₁₁₄pMA(Az)₂₄ and p(EO)₁₁₄ were miscible without in the p(EO) content below 60%.     

Nano-scale structure change of amphiphilic di-block copolymer by blend

The phase transition and nano-scale ordered structure of four types of blends prepared from four di-block copolymers, consisting of hydrophilic poly(ethylenoxide) and hydrophobic poly(methacrylate) derivative, PEO_m-b-PMA(Az)_n having different PEO molecular length and same degree of polymerization of PMA(Az) were investigated. All blend systems formed hexagonal packed PEO cylinder structure, which was same with the nano-scale structure of these parent block copolymers. The SAXS and AFM observation suggested that the size of hexagonal structure of blend was larger than the average size of parent block copolymers. The melting enthalpy of PEO in blends was larger than the average value of parent block copolymers. DSC, SAXS and AFM observations indicated the miscible blend systems.     

Isotropic transition of amphiphilic side-chain type liquid crystalline di-block copolymers

The effects of nitrogen (N₂) pressure on amphiphilic di-block copolymer, PEO₁₁₄-b-PMA(Az)₄₀, were investigated by scanning transitiometry. The isotropic transition temperature increased with the increase of pressure above 20 MPa. The hydrostatic pressure effects evaluated with the Clapeyron equation were smaller than the value obtained by mercury as a pressurizing medium because the amount of absorbed gas decreases the volume change at the isotropic transition.     

A starlike amphiphilic graft copolymer with hydrophilic poly(acrylic acid) backbones and hydrophobic polystyrene side chains

A well‐defined starlike amphiphilic graft copolymer bearing hydrophilic poly(acrylic acid) backbones and hydrophobic polystyrene side chains was synthesized by successive atom transfer radical polymerization followed by the hydrolysis of poly‐(methoxymethyl acrylate) backbone. A grafting‐from strategy was employed for the synthesis of a graft copolymer with narrow molecular weight distribution. Hydrophobic polystyrene side chains were connected to the backbones through stable C? C bonds. The poly(methoxymethyl acrylate) backbones can be easily hydrolyzed with HCl without affecting the hydrophobic polystyrene side chains. This kind of amphiphilic graft copolymer can form stable sphere micelles in water. The sizes of the micelles were dependent on the ionic strength and pH value. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3687–3697, 2007     

Nickel dithiolene complexes encapsulated in biocompatible amphiphilic diblock copolymer nanoparticles

The goal of this study is to prepare novel hybrid nanoparticles, in the form of micellar nanoparticles in aqueous media, which will combine the properties of the amphiphilic diblock copolymers (such as PEO‐b‐PPhOx and PI‐b‐PEO) with the ones of the nickel 1,2‐dithiolene (1,2‐Ni DT) complexes. The structural and morphological analysis of these nanoparticles have revealed that they can be promising for photodynamic therapy and near‐infrared (NIR) optical imaging due to their size and absorption in NIR. The micellar nanoparticles have been studied not only in aqueous solutions but also under other physiological conditions, that is, PBS and PBS‐FBS buffer solutions. Their solutions are characterized by several methods, including UV–vis spectroscopy, light scattering, and FTIR. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 2507–2513     

Well‐defined amphiphilic graft copolymer consisting of hydrophilic poly(acrylic acid) backbone and hydrophobic poly(vinyl acetate) side chains

A series of well‐defined amphiphilic graft copolymers containing hydrophilic poly(acrylic acid) (PAA) backbone and hydrophobic poly(vinyl acetate) (PVAc) side chains were synthesized via sequential reversible addition‐fragmentation chain transfer (RAFT) polymerization followed by selective hydrolysis of poly(tert‐butyl acrylate) backbone. A new Br‐containing acrylate monomer, tert‐butyl 2‐((2‐bromopropanoyloxy)methyl) acrylate, was first prepared, which can be polymerized via RAFT in a controlled way to obtain a well‐defined homopolymer with narrow molecular weight distribution (M_w/M_n = 1.08). This homopolymer was transformed into xanthate‐functionalized macromolecular chain transfer agent by reacting with o‐ethyl xanthic acid potassium salt. Grafting‐from strategy was employed to synthesize PtBA‐g‐PVAc well‐defined graft copolymers with narrow molecular weight distributions (M_w/M_n < 1.40) via RAFT of vinyl acetate using macromolecular chain transfer agent. The final PAA‐g‐PVAc amphiphilic graft copolymers were obtained by selective acidic hydrolysis of PtBA backbone in acidic environment without affecting the side chains. The critical micelle concentrations in aqueous media were determined by fluorescence probe technique. The micelle morphologies were found to be spheres. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 6032–6043, 2009     

Synthesis of an amphiphilic spiro-multiblock copolymer via thiol-ene click chemistry

A multiblock [poly(ethylene oxide)-b-spiro-polystyrene] ([(PEO-b-spiro-PS)]) copolymer with a topologically novel architecture was synthesized using thiol-ene step-growth polymerization reaction. Spiro-PS with dimercapto groups as the hard segment was synthesized in three main steps: (a) preparation of tetra-arm PS by atom transfer radical polymerization and the conversion of the chain-end group to azide functionality, (b) alkyne-azide click coupling reaction to synthesize a tricyclic PS, and (c) tactical ring opening of the tricyclic PS through disulfide/thiol redox reaction. The PEO soft segment was obtained as chain-ends modified with norbornene groups. Finally, the hydrothiolation of the highly reactive norbornene chain-ends of polyethylene glycol with the dimercapto groups of spiro-PS produced the multiblock ([(PEO-b-spiro-PS)]) copolymer in quantitative yield. The multiblock copolymer was characterized using size-exclusion chromatography, proton nuclear magnetic resonance spectroscopy, Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, and Raman spectroscopy. © 2019 Wiley Periodicals, Inc. J. Polym. Sci. 2020 , 58, 132–138     

Design of controlled releasing system: Synthesis of an amphiphilic copolymer endowed with acid‐labile side chains based on quaternarization of amine‐containing prepolymer with benzyl halide having acetal moiety

A methacrylate having a hydrophilic poly(ethylene glycol) chain and 2‐(N,N‐dimethylamino)ethyl methacrylate were radically copolymerized to obtain a statistical hydrophilic copolymer having tertiary amino groups in the side chains. The obtained polymeric amine was quantitatively quaternarized by a benzyl chloride‐type molecule having an acetal moiety derived from geraniol, which is a hydrophobic alcohol widely used as a fragrance ingredient. The resulting copolymer, which had PEG chain and the quaternary ammonium moieties as hydrophiles and the acetal moieties as hydrophobes, exhibited amphiphilicity to form stable associates in water. The acetal moieties were stable for 30 days at pH 9, while they were gradually hydrolyzed at pH 4 to release geraniol continuously at least for 30 days, confirming the potential applicability of the copolymer to a controlled releasing system of functional molecules. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3241–3247, 2009     

Synthesis of an Amphiphilic Brush Copolymer by a Highly Efficient “Grafting onto” Approach via CO2 Chemistry

A novel and robust route for the synthesis of a new amphiphilic brush copolymer, poly(glycidyl methacrylate)‐graft‐polyethylene glycol (PGMA‐g‐PEG), with high grafting densities of 97%–98% through a “grafting onto” method via carbon dioxide chemistry is reported. PGMA‐g‐PEG can self‐assemble and form stable spherical core–shell micelles in aqueous solution. Besides, the obtained PGMA‐g‐PEG polymer contains hydroxyurethane structures as the junction sites between the PGMA backbone and PEG side chain, which can be used for further modification.

     

Surfactant‐free synthesis of amphiphilic diblock copolymer in aqueous phase by a self‐stability process

Amphiphilic polymeric particles with hydrophobic cores and hydrophilic shells were prepared via living radical emulsion polymerization of styrene using a water‐soluble poly(acrylamide)‐based macro‐RAFT agent in aqueous solution in the absence of any surfactants. Firstly, the homopolymerization of acrylamide (AM) was carried out in aqueous phase by reversible addition‐fragmentation chain transfer radical polymerization (RAFT) using a trithiocarbonate as a chain transfer agent. Then the PAM‐based macro‐RAFT agent has been used as a water‐soluble macromolecular chain transfer agent in the batch emulsion polymerization of Styrene (St) free of surfactants. The RAFT controlled growth of hydrophobic block led to the formation of well‐defined poly(acrylamide)‐copolystyrene amphiphilic copolymer, which was able to work as a polymeric stabilizer (self‐stability). Finally, very stable latex was prepared, having no visible phase separation for several months. FTIR and ¹H‐NMR measurements showed that the product was the block copolymer PAM‐co‐PS in the form of stable latex. Atomic force microscope (AFM), transmission electron microscope (TEM), and dynamic light scattering (DLS) studies indicated that the nanoparticles have a narrow particle size distribution and the average particle hydrodynamic radius was kept in the diameter of 58 nm. Core‐shell structure of the copolymer was also recorded by TEM. The mechanism of the self‐stability of polymer particles during the polymerization in the absence of surfactants was studied. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3098–3107, 2008     

Synthesis and characterization of a film‐forming,crosslinked, amphiphilic block copolymer of butadiene and acrylamide

An amphiphilic block copolymer of acrylamide and butadiene was synthesized by the polymerization of acrylamide in the presence of the crosslinker N,N′‐methylene bisacrylamide initiated by a hydroxyl‐terminated polybutadiene/V(V) macroredox initiator. The product had good film‐forming ability. It was characterized by IR and NMR spectroscopy, viscosity, swelling, and microhardness measurements, scanning electron micrography, and differential scanning calorimetry. A good film was obtained from the block copolymer with a greater proportion of butadiene; it had greater permeability for nonpolar solvents, and it was poorly permeable to water and other polar solvents. The film swelled in polar and nonpolar solvents and had almost the same capacity for the loading and release of hydrophilic and hydrophobic dyes. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3290–3303, 2006     

Conformation of amphiphilic branch chain in copolymer surfactants on interface

The conformation of amphiphilic branch chain in a new type of copolymer surfactants on interface was studied. The results of laser light scattering demonstrated that the branch chain can only lie on the air/water interface. By means of XPS measurement with variable angles, the molecular conformations in different thickness of the copolymer layer were obtained. Depending on the chemical nature of the copolymer surfactants, the oxyethylene segments of the branch chains will have loop-train, train, or loop molecule conformations on the surface. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 827–830, 1997     

Star-graft copolymers. Synthesis of amphiphilic graft copolymers with star-branched poly(oxyethylene) side chains

The synthesis of novel amphiphilic star-graft (SG) copolymers containing hydrophilic poly(oxyethylene) (PEO) side chains attached to a hydrophobic backbone by multifunctional entity is reported. In a first step poly(phthalimidoacrylate-co-styrene) was converted into polymers containing different number of multifunctional branching cites distributed along the main chain by partial aminolysis of the phthalimidoacrylate units with tris(hydroxymethyl)aminomethane. In the second step, these reactive copolymers yielded SG copolymers with different number of star-shaped PEO side groups by reaction with isocyanato terminated methoxy–PEO. The copolymers were characterized by size-exclusion chromatography, IR-, and NMR-spectroscopy. Their thermal properties were examined by thermal gravimetric analysis and differential scanning calorimetry. The studies indicate that the grafting degree and hydrogen bonding determine to a great extent the behavior of the SG copolymers in solid state and in solution. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 673–679, 1997     

Convenient synthesis of thermo‐responsive PtBA‐g‐PPEGMEMA well‐defined amphiphilic graft copolymer without polymeric functional group transformation

A series of well‐defined amphiphilic graft copolymers bearing hydrophobic poly(tert‐butyl acrylate) backbone and hydrophilic poly[poly(ethylene glycol) methyl ether methacrylate)] (PPEGMEMA) side chains were synthesized by sequential reversible addition fragmentation chain transfer (RAFT) polymerization and single‐electron‐transfer living radical polymerization (SET‐LRP) without any polymeric functional group transformation. A new Br‐containing acrylate monomer, tert‐butyl 2‐((2‐bromoisobutanoyloxy)methyl)acrylate (tBBIBMA), was first prepared, which can be homopolymerized by RAFT to give a well‐defined PtBBIBMA homopolymer with a narrow molecular weight distribution (M_w/M_n = 1.15). This homopolymer with pendant Br initiation group in every repeating unit initiated SET‐LRP of PEGMEMA at 45 °C using CuBr/dHbpy as catalytic system to afford well‐defined PtBBIBMA‐g‐PPEGMEMA graft copolymers via the grafting‐from strategy. The self‐assembly behavior of the obtained graft copolymers in aqueous media was investigated by fluorescence spectroscopy and TEM. These copolymers were found to be stimuli‐responsive to both temperature and ions. Finally, poly(acrylic acid)‐g‐PPEGMEMA double hydrophilic graft copolymers were obtained by selective acidic hydrolysis of hydrophobic PtBA backbone while PPEGMEMA side chains kept inert. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Poly(ethylene glycol)/poly(ethyl cyanoacrylate) amphiphilic triblock copolymer nanoparticles as delivery vehicles for dexamethasone

Amphiphilic triblock copolymers, poly(ethyl cyanoacrylate)‐b‐poly(ethylene glycol)‐b‐poly(ethyl cyanoacrylate) (PECA‐b‐PEG‐b‐PECA), were synthesized via oxyanion‐initiated polymerization with sodium alcoholate‐terminated PEG as macroinitiator. PECA‐b‐PEG‐b‐PECA were characterized by gel permeation chromatography system, ¹H NMR and FTIR. The results indicate that the copolymerization is well controlled with narrow molecular weight distribution. The dexamethasone (DXM)‐loaded PECA‐b‐PEG‐b‐PECA nanoparticles (NPs) were prepared by nanoprecipitation technique and then characterized by Laser Particle Size Analyzer, ¹H NMR and transmission electron microscopy. The drug‐loaded PECA‐b‐PEG‐b‐PECA NPs are of spherical shape with average size of less than 100 nm. The drug‐loaded amount (DLA) and encapsulation efficiency of DLNPs were investigated by HPLC. The results show that DXM can be effectively incorporated into PECA‐b‐PEG‐b‐PECA NPs, which provides an optional delivery system for DXM and other hydrophobic drugs. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 7809–7815, 2008     

Solid‐supported amphiphilic triblock copolymer membranes grafted from gold surface

Gold‐supported amphiphilic triblock copolymer brushes composed of two hydrophilic poly(2‐hydroxyethyl methacrylate) (PHEMA) blocks and a hydrophobic poly(n‐butyl methacrylate) (PBMA) middle part were synthesized using a surface‐initiated ATRP. Attenuated total reflectance Fourier transform infrared spectroscopy, polarization modulation infrared reflection absorption spectroscopy (PM‐IRRAS), ellipsometry, contact angle measurements, and atomic force microscopy were used for the characterization of PHEMA‐co‐PBMA‐co‐PHEMA brushes. The PM‐IRRAS analysis revealed an increase of the chain tilt toward the gold surface during growth of the individual blocks. We suggest that the orientation of the amphiphilic polymer brushes is influenced by both the chain length and the interchain interactions. Additionally, a detachment of the polymer membranes from the solid support and subsequent gel permeation chromatography analyses allowed us to establish their compositions. We applied block‐selective solvents (water and hexane) as well as a good solvent for the whole polymer chain (ethanol) to study the morphology and solvent responsive behavior of the amphiphilic brushes. The presented results could serve as a good starting point for the fabrication of functional solid‐supported membranes for biosensing applications. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1–13, 2009     

两亲性嵌段共聚物PGMA-b-PMAPEG的制备及其胶束的布洛芬药物控制释放性能

利用自由基可逆加成-断链链转移(RAFT)活性/可控聚合法成功合成了两亲性嵌段共聚物聚(甲基丙烯酸缩水甘油酯)-b聚(甲基丙烯酸聚乙二醇酯)(PGMA-b-PMAPEG).利用傅立叶变换红外光谱、核磁共振谱仪、凝胶渗透色谱仪及透射电镜等分析了所合成聚合物的结构、胶束粒径及形貌.以布洛芬作为模型药物负载于聚合物胶束内,考...     

Chromatography of amphiphilic graft copolymers

Amphiphilic comb polymers were prepared through grafting poly(ethylene glycol) methyl ether (MPEG 2000) onto acrylic and methacrylic copolymers. The graft copolymers were purified from unreacted MPEG by partition chromatography on methanol pretreated fibrous cellulose using ethyl acetate and methanol as eluents. The separation was found to depend on the water contents of the cellulose and the eluents. It is proposed that one parameter of importance for the chromatographic separation is the formation of hydrated inverted micelles. The amphiphilic comb polymers were shown by gel chromatography on Sepharose to form high molecular weight aggregates in water. On addition of sodium lauryl sulphate or inorganic salts to the eluent at low ionic strengths these aggregates dissociated and were fractionated by the gel. It was also shown that on GPC in THF solution on Styragel columns the polymers exhibited apparent molecular weights equal or smaller than those of the corresponding backbones. This effect may be a consequence of the graft copolymers having relatively small hydrodynamic volumes, and this idea is supported by the fact that their intrinsic viscosities generally were lower than those of the backbones. However, adsorption on the Styragel columns also may be of importance.     

Synthesis and characterization of hyperbranched amphiphilic block copolymers prepared via self‐condensing RAFT polymerization

Four families of hyperbranched amphiphilic block copolymers of styrene (Sty, less polar monomer) and 2‐vinylpyridine (2VPy, one of the two more polar monomers) or 4‐vinylpyridine (4VPy, the other polar monomer) were prepared via self‐condensing vinyl reversible addition‐fragmentation chain transfer polymerization (SCVP‐RAFT). Two families contained 4VPy as the more polar monomer, one of which possessing a Sty‐b‐4VPy architecture, and the other possessing the reverse block architecture. The other two families bore 2VPy as the more polar monomer and had either a 2VPy‐b‐Sty or a Sty‐b‐2VPy architecture. Characterization of the hyperbranched block copolymers in terms of their molecular weights and compositions indicated better control when the VPy monomers were polymerized first. Control over the molecular weights of the hyperbranched copolymers was also confirmed with the aminolysis of the dithioester moiety at the branching points to produce linear polymers with number‐average molecular weights slightly greater than the theoretically expected ones, due to recombination of the resulting thiol‐terminated linear polymers. The amphiphilicity of the hyperbranched copolymers led to their self‐assembly in selective solvents, which was probed using atomic force microscopy and dynamic light scattering, which indicated the formation of large spherical micelles of uniform diameter. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 1310–1319