Effect of core-shell micelle formation on the redox properties of phenothiazine-labeled poly(ethyl glycidy ether)-block-poly(ethylene oxide)

Redox properties of phenothiazine-labeled poly(ethyl glycidy ether)-block-poly(ethylene oxide) (PT-EGE_n-b-EO_m) are reversibly changed by core-shell micelle formation. In the temperature range higher than the critical micellization temperature (cmt), the anodic potential of PT group positively shifts and concomitantly its anodic current decrease, or levels off compared to those of the reference polymer PT-EO_m without the thermo-responsive EGE_n segment. The former alteration is caused by incorporation of hydrophobic PT groups into a core of the micelle and the latter by the decrease in the diffusion coefficient of PT groups due to formation of the core-shell micelles. The cmt value and the temperature-dependent alteration in the redox properties strongly depend on the polymer structure, especially the length of thermo-responsive EGE_n segment. The electrochemically determined hydrodynamic radii of the polymer aggregates seem to be overestimated, compared to the values reported for the aggregates of other thermo-responsive polymers with similar molecular weights, implying the presence of electrochemically inactive PT groups in the copolymers having longer thermo-responsive segments.     

Temperature-sensitive behaviour of poly(glycidol)-b-poly(N-isopropylacrylamide) block copolymers

Temperature-sensitive poly(glycidol)-b-poly(N-isopropylacrylamide) block copolymers (PGl₅₅PNIPAAm_y) were synthesised and their aqueous solutions investigated by different methods including differential scanning calorimetry (DSC), UV-VIS spectroscopy as well as dynamic and static light scattering. The cloud point temperature (T _c) depended on the composition of the investigated block copolymers and increased with decreasing length of the PNIPAAm block in PGl₅₅PNIPAAm_y copolymers. In contrast, the enthalpy of phase separation of PNIPAAm segments measured by DSC decreased with decreasing length of the PNIPAAm block in the polymer. These findings can be correlated with the behaviour of homo-PNIPAAm with similar molecular weights indicating that the influence of PGl on the local environment and phase separation of PNIPAAm chains is similar to the influence observed for PNIPAAm chains bearing different low molecular weight end group. Using DLS measurement, it was shown that the aggregation process depended on the PGl/PNIPAAm block ratio. If the PGl/PNIPAAm ratio was low, stable core-shell aggregates were formed. In contrast, the tendency to formation of large unstable, loose aggregates was observed for copolymers with high PGl/PNIPAAm ratio.     

Aggregation behavior of thermo-responsive poly(2-oxazoline)s at the cloud point investigated by FCS and SANS

We have studied different thermo-responsive poly(2-oxazoline)s with iso-propyl (iPrOx) and n-propyl (nPrOx) pendant groups in aqueous solutions, where they exhibit lower critical solution temperature behavior. This paper focuses on the effect of the degree of polymerization, n, the concentration, c, in the dilute regime, and the presence of hydrophobic moieties. The cloud points were investigated as a function of the degree of polymerization, n, and of the polymer concentration, c. The aggregation behavior near the cloud point was studied by temperature-resolved small-angle neutron scattering and fluorescence correlation spectroscopy, i.e., a combination of ensemble and single molecule methods. We found that at the cloud points, large aggregates are formed and that the cloud points depend strongly on both, n and c. Diblock copolymers from iPrOx and nPrOx form large aggregates already at the cloud point of PnPrOx, and, unexpectedly, no micelles are observed between the cloud points of the two blocks. Gradient copolymers from iPrOx and n-nonyl-2-oxazoline (NOx) display a complex aggregation behavior resulting from the interplay between intra- and intermolecular association mediated by the hydrophobic NOx blocks. Above the cloud point, an intermediate temperature regime with a width of a few Kelvin was found with small but stable polymer aggregates. Only at higher temperatures, larger aggregates are found in significant number.     

Solubilization of C60 by micellization with a thermoresponsive block copolymer in water: Characterization,singlet oxygen generation,and DNA photocleavage

Water‐soluble diblock copolymer, poly(N‐isopropylacrylamide)‐block‐poly(N‐vinyl‐2‐pyrroridone) (PNIPAM_m‐b‐PNVP_n), was found to associate with fullerene (C₆₀), and thus C₆₀ can be solubilized in water. The 63C₆₀/PNIPAM_m‐b‐PNVP_n micelle formed a core‐shell micelle‐like aggregate comprising a C₆₀/PNVP hydrophobic core and a thermoresponsive PNIPAM shell. The C₆₀‐containing polymer micelle formation and its thermoresponsive behavior were characterized using light scattering and ¹H NMR techniques. The hydrodynamic radius (R_h) of the C₆₀‐bound polymer micelle increased with increasing temperature, which was ascribed to the hydrophobic association between dehydrated PNIPAM shells above lower critical solution temperature (LCST). ¹H NMR data suggest that the motion of the PNIPAM block is restricted above LCST due to the dehydration of the PNIPAM shell in water. The generation of singlet oxygen by photosensitization by the C₆₀‐bound polymer micelle was confirmed from photooxidation of 9,10‐anthracenedipropionic acid. Furthermore, DNA was found to be cleaved by visible light irradiation in the presence of the C₆₀‐bound polymer micelle. Therefore, there may be a hope for a pharmaceutical application of the C₆₀‐bound polymer micelle to cancer photodynamic therapy. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011.     

Micellization of non-surface-active diblock copolymers in water. Special characteristics of poly(styrene)-block-poly(styrenesulfonate)

Strongly ionized amphiphilic diblock copolymers of poly(styrene)-b-poly(styrenesulfonate) with various hydrophilic and hydrophobic chain lengths were synthesized by living radical polymerization, and their properties and self-assembling behavior were systematically investigated by surface tension measurement, foam formation, hydrophobic dye solubilization, X-ray reflectivity, dynamic light scattering, small-angle neutron scattering, small-angle X-ray scattering, and atomic force microscope techniques. These copolymer solutions in pure water did not show a decrease of surface tension with increasing polymer concentration. The solutions also did not show foam formation, and no adsorption at the air/water interface was confirmed by reflectivity experiments. However, in 0.5 M NaCl aq solutions polymer adsorption and foam formation were observed. The critical micelle concentration (cmc) was observed by the dye solubilization experiment in both the solutions with and without added salt, and by dynamic light scattering we confirmed the existence of polymer micelles in solution, even though there was no adsorption of polymer molecules at the water surface in the solution without salt. By the small-angle scattering technique, we confirmed that the micelles have a well-defined core-shell structure and their sizes were 100-150 A depending on the hydrophobic and hydrophilic chain length ratio. The micelle size and shape were unaffected by addition of up to 0.5 M salt. The absence of polymer adsorption at the water surface with micelle formation in a bulk solution, which is now known as a universal characteristic for strongly ionized amphiphilic block copolymers, was attributed to the image charge effect at the air/water interface due to the many charges on the hydrophilic segment.     

Micelle Formation and Counterion Binding of Dodecylammonium Alkanesulfonates in Water at Different Temperatures

A temperature study was performed on micelle formation of a series of homologous cationic surfactants having organic counterions (alkanesulfonates) with carbon numbers ranging from 1 to 4: dodecylammonium salts of methanesulfonate (DAMS), ethanesulfonate (DAES), propanesulfonate (DAPS), and butanesulfonate (DABS) in water. The critical micelle concentrations (CMCs) and the degree of counterion binding (β) were determined at different temperatures ranging from 5 to 50°C by means of conventional electric conductance measurements. From the temperature dependence of β as well as CMC, Gibbs energy ΔG⁰_m, enthalpy ΔH⁰_m, and entropy ΔS⁰_m, on micelle formation, were estimated for the respective surfactants. As for the temperature dependence of CMC for these surfactants, the temperature-CMC curves have a minimum around 30°C and show that the CMC at each temperature is lowered by about 3 mmol dm^-3 per methylene group in the alkyl chain of the counterions. The relationship between β and temperature suggested that the counterion of MS^- behaves most similarly to common univalent ions such as halide ions. In contrast, PS^- and BS^-, having a stronger ability to lower CMC and to promote association of surfactant ions with counterions as well as of surfactant ions themselves, behave more like those of surfactant ions, and ES^- shows the most complicated character between those of common univalent ions and organic ions. However, the temperature dependence of enthalpy change, ΔH⁰_m demonstrates that these four surfactants are divided into two groups: (1) DAMS and DAES and (2) DAPS and DABS. In addition, the entropy change ΔS⁰_m as a function of alkyl chain length gives evidence that the contribution of the entropy term to the Gibbs energy on micelle formation clearly separates between DAES (m = 2) and DAPS (m = 3). A similar discontinuity is found even in the plot of ΔG⁰_m versus carbon atom number of alkyl chain, m, and in the plot of ΔG⁰_m versus estimated hydrodynamic radius of counterions. All the results obtained have indicated that lengthening the alkyl chains initially hinders micelle formation, but the longer chains are markedly effective in lowering the CMC and probably in increasing the aggregation number, owing to enhanced hydrophobic interaction between counterion and the micellar surface and/or core.     

Poly(2-(dimethylamino)ethyl methacrylate)-b-poly(hydroxypropyl methacrylate) copolymers/bovine serum albumin complexes in aqueous solutions

Complexation ability of poly(2-(dimethylamino)ethyl methacrylate)-b-poly(hydroxy propyl methacrylate) (PDMAEMA-b-PHPMA) amphiphilic doubly thermo-responsive block copolymers, and their quaternized counterparts QPDMAEMA-b-PHPMA, toward bovine serum albumin (BSA) is studied in aqueous solutions. The PDMAEMA-b-PHPMA amphiphilic block copolymers self-assemble in nanostructured aggregates with PDMAEMA coronas having different inner structure and micro-polarity depending on the solubilization protocol utilized when inserted in aqueous media. By incorporating different BSA concentrations, we investigate the copolymer–protein interactions by light scattering measurements in aqueous solutions in a broad temperature range, utilizing different solubilization protocols for the copolymers. Fluorescence spectroscopy and ζ-potential measurements were also utilized to investigate the structure and properties of the copolymer/protein complexes formed in each case. Such knowledge may lead to a better understanding of the inner structure and micro polarity of the nanostructured aggregates formed by the novel (Q)PDMAEMA-b-PHPMA copolymers, along with their potential abilities in nanocarrier formation, protein complexation, stabilization, and delivery.     

Effects of polystyrene-b-poly(aminomethyl styrene)s as stabilizers on dispersion polymerization of styrene in alcoholic media

The effects of polystyrene-b-poly(aminomethyl styrene) (PS_n-b-PAMS_m) stabilizers on the particle size (D_n) and size distribution (PSD) in dispersion polymerization of styrene were investigated. The block copolymers, PS_n-b-PAMS_m, were prepared as follows: (i) atom transfer radical polymerization (ATRP) of styrene (PS-Br), (ii) ATRP of vinylbenzylphthalimide with the PS-Br (PS-b-PVBP), and (iii) treatment of the PS-b-PVBP with hydrazine. When the dispersion polymerization of styrene proceeded at 60 °C in ethanol with PS₁₉-b-PAMS₁₃₀ stabilizer, spherical polystyrene particles with D_n=0.91 μm (PSD = 1.01) were obtained. The particle size was strongly affected by the copolymer composition. With an increase in PAMS block length from m=54 to 100 in PS₁₇-b-PAMS_m, particle diameter became smaller from 1.55 to 0.91 μm. On the other hand, an increase in the length from m=20 to 82 in PS₃₄-b-PAMS_ms caused an increase in particle size from 0.35 to 0.70 μm. Titration of the particles suggests that 14–81% of stabilizers used in the polymerization system were attached on the polystyrene particle surfaces, depending on the composition of the block copolymers. Thus, for the dispersion polymerization of styrene, PS_n-b-PAMS_m block copolymers have both functions as a stabilizer during polymerization and surface-modification sites of polystyrene particles.     

Synthesis and structure of cis-[RuCl(bpzm)(κ1-P-dpim)(κ2-P,N-dpim)]Cl·(CHCl3)5. Stability of [Cl(HCCl3) n ]− aggregates

The reaction of [RuCl₂(cod)(bpzm)] [cod = 1,5-cyclooctadiene, bpzm = bis(pyrazol-1-yl)methane] with 2-diphenylphosphino-1-methylimidazole (dpim) and crystallisation from CHCl₃ yielded crystals of cis-[RuCl(κ²-N,N-bpzm)(κ¹-P-dpim)(κ²-P,N-dpim)][Cl(CHCl₃)₄]·CHCl₃, (1√(CHCl₃)₅), in which the Cl^?  counteranion was solvated by four CHCl₃ molecules and interacted with the most positive region of the cation. The structure of the anionic entity and the presence of non-covalent interactions were studied. Theoretical calculations allowed the evaluation of the stability of [Cl(CHCl₃) _n ]^?  aggregates. A pronounced stability was found for aggregates with n = 6 with an increasing charge transfer from the chloride ion to the CHCl₃ molecules from n = 1 to 6. A literature survey on the occurrence of anionic species [Cl(CXCl₃) _n (HB) _m ]^?  (X = H or D; HB = hydrogen bonds with the cation) in solid state structures was carried out and the findings correlated with the results of computational studies. A stabilisation effect of a Cl…Cl interaction was demonstrated by a natural bond orbitals (NBO) analysis.     

Polyion micelles with diphase-segregated core: electrostatic self-assembly of poly(ethylene glycol)-<Emphasis Type="Italic">block</Emphasis>-poly(4-vinylpyridium) and tetrakis (4-sulfonatophenyl) porphyrin in solution

The polyion micelles were prepared with poly(ethylene glycol)-block-poly(4-vinylpyridium) (PEG₁₁₄-b-P(4-VPH+)₃₅) and tetrakis (4-sulfonatophenyl) porphyrin (TPPS) in acid aqueous solution. Micellization was investigated by using a combination of static and dynamic laser scattering. UV–Vis spectroscopy revealed that the H- and J-type aggregates of TPPS were formed in the micellar core. Transmission electron microscopy studies of the polyion micelles show that the obtained polyion micelles take a diphase-segregated core, the polymer phase and the incompatible TPPS aggregates phase.     

Micelle-Forming and Catalytic Properties of n-Alkyl(2-hydroxyethyl)dimethylammonium Bromides in the Phosphorylation of Tetrakis(dimethylaminomethyl)calixresorcin[4]arene

Micelle formation by n-alkyl(2-hydroxyethyl)dimethylammonium bromides in chloroform was studied by dielcometric titration and kinetic method. Increase in the length of the hydrocarbon chain leads to reduced critical micelle concentration. The region of structural reorganization of micelles was determined. n-Alkyl(2-hydroxyethyl)dimethylammonium bromides catalyze phosphorylation of tetrakis(dimethylamino- methyl)calixresorcin[4]arene. The catalytic activity of micelles depends on the hydrophobic properties and concentration of the surface-active substance, as well as on structural features of its aggregates.     

Aggregation Behavior of Pluronic-L64 in Presence of Sodium Dodecyl Sulphate in Water

The effect of sodium dodecyl sulfate (SDS) on the micellization and aggregation behavior of a poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) (PEO-PPO-PEO) amphiphilic copolymer (Pluronic L64: EO₁₃ PO₃₀ EO₁₃) have been investigated by various techniques like, cloud point, viscosity, isothermal titration calorimetry (ITC), differential scanning calorimetry (DSC), fluorescence spectroscopy, room temperature phosphorescence (RTP), and small angle neutron scattering (SANS). Addition of SDS in L64 solutions shows mark alteration of different properties. We observed synergistic interaction between SDS and Pluronic L64. The changes in the critical micelle concentration (CMC), critical micelle temperature (CMT), cloud point (CP), micelle size, and shape has been correlated and reported in terms of structure dynamics and mechanics. The ITC titrations have been used to explore the different stages of binding and interactions of SDS with L64. The enthalpies of aggregation for copolymer-SDS aggregates binding, organizational change of bound aggregates, and the threshold concentrations of SDS in the presence of copolymer were estimated directly from ITC titration curves. The effect of temperature on enthalpy values has been reported in terms of different aggregation state. Fluorescence and RTP for L64 were used to investigate the change in micellar environment on the addition of SDS at different temperature. Appearance and shifting of SANS peaks have been used to monitor the size and inter micellar interaction on addition of SDS in L64 solution. Cloud point and viscosity elaborate the penetration of SDS molecule in L64 micelle and hence changing the micellar architect.     

Side-chain crystallinity,heat of melting,and thermal transitions in poly[N-(10-n-alkyloxycarbonyl-n-decyl)maleimides] (PEMI)

The heat of melting, the melting temperature T_m, and the sub-T_g transition temperature have been studied from –120°C to above T_m in a series of 11 poly[N-(10-n-alkyloxycarbonyl-n-decyl)]-maleimides (PEMI). Side-chains from ethyl to n-docosyl with n even have been included. The contribution to the heat of melting per methylene group shows that the hexagonal paraffin crystal modification is present in these poly(N-maleimides), in agreement with x-ray data for the same compounds. The enthalpy data show that only a part of the outer methylene groups are present in the crystalline aggregates. Furthermore, DSC traces exhibit a typical distribution of crystallite sizes, which become narrower as the side-chains become longer. The critical chain length needed to form a stable nucleus includes nine methylene groups in the outer part of the n-alkyl side-chain. The influence of the side-chain length and crystallinity on the γ-transition temperature of these polymers was also investigated. In the range where these polymers are essentially amorphous the sub-T_g transition temperature decreases continuously as the number of methylene groups in the side-chain increases. This transition is attributed to internal motion within the external side-group without any interaction with the main chain. This is presumably made possibly by the partial rotation of the oxycarbonyl group. We suggest that this transition is similar to the well known γ transition which has been attributed to various segmental motions in all ethylene copolymers and in all homopolymers containing a determined number of? CH₂? units in the main-chain or in the side-chain. Estimates based on the chemical structure, yield a value for the γ transition of ? CH₂? similar to that measured by other methods in polyethylene and related materials.     

Micelle formation of ethoxylated nonyl-phenols in aqueous solutions

The micelle formation of nonyl-phenols with various numbers of ethoxy groups (n _EO=10–40) was investigated in aqueous solutions and the study was focussed on the effect of temperature (293–323 K), the chain length and the inorganic electrolyte (NaCl) on the critical micelle concentration (c.m.c).The c.m.c. was determined by surface tension and interfacial tension measurements in a water/n-octane system. On the basis of the actual c.m.c. and its temperature dependence the thermodynamic functions of micelle formation (H° _m,S°_m,G°_m) were also calculated. The latter study comprised the determination of the thermodynamic function for unity ethoxy groups ((Y° _m)) as a function ofn _EO.According to the experimental results the micellar solutions are the more stable, the smaller the number of ethoxy groups in the tenside molecule and the higher the temperature as well as the electrolyte content of the system.     

N,N-Bis[ethoxy(methyl)silylmethyl]methylamines MeN[CH2SiMem(OEt)3-m]2 (m = 0-2). Synthesis and Reactions with Phenol

Previously unknown N,N-bis[ethoxy(methyl)silylmethyl]amines MeN[CH₂SiMe_m(OEt)_3-m ]2 (m = 0-2) were synthesized. According to UV spectral data, only MeN[CH₂SiMe₂(OEt)]₂ form hydrogen bond with phenol in a heptane solution. The amines with m = 0 and 1 fail to forms hydrogen bond with phenol [under the same conditions, N-(triethoxysilylmethyl)dimethylamine Me₂NCH₂Si(OEt)₃ forms a strong hydrogen bond with phenol]. All the amines (m = 0-2) enter transetherification with phenol to give compounds of the general formula MeN[CH₂SiMe_m m(OPh) _n (OEt)3-m-n]₂ (m = 0-2, n = 1-3). Refluxing of N,N-bis[ethoxy(methyl) silylmethyl]amines with excess phenol results in cleavage of the Si-C bond by phenol, providing phenoxysilanes Me_mmSi(OPh)4-m (m = 0-2) and trimethylamine.     

Assembly of amphiphilic poly[2‐(methacryloyloxy)ethyl phosphorylcholine] with cholesteryl moieties as terminal groups

Poly[2‐(methacryloyloxy)ethyl phosphorylcholine]s (PMPCs) with one pendant cholesteryl moiety at the polymer end (PMPC‐Chol‐I and PMPC‐Chol‐II) and two pendant cholesteryl moieties at both polymer ends as terminal groups (PMPC‐2Chol‐I and PMPC‐2Chol‐II) were prepared by the radical polymerization of 2‐(methacryloyloxy)ethyl phosphorylcholine initiated with 4,4′‐azobis[(3‐cholesteryl)‐4‐cyanopentanoate] in the presence of 2‐mercaptoethanol or thiocholesterol as chain‐transfer reagents, respectively. The self‐organization of PMPC‐Chol and PMPC‐2Chol was analyzed with fluorescence and ¹H NMR measurements. The critical micelle concentrations of PMPC‐Chol‐I with a degree of polymerization (P_n) of 91 and of PMPC‐2Chol‐I with a P_n value of 165 were 250 and 27 mg L^?1, respectively. The blood compatibility of PMPC‐2Chol was evaluated from the Michaelis constant (K_m) for the enzymatic reaction of thrombin and a synthetic substrate, S‐2238, in the presence of PMPC‐2Chol. K_m was 0.07, 0.05, and 0.56 for PMPC‐2Chol‐I with P_n = 165, PMPC‐2Chol‐II with P_n = 38, and PMPC (an intrinsic viscosity of 0.54 dL g^?1) initiated with 2,2′‐azobisisobutyronnitrile in the absence of chain transfer agent, respectively. A mixture of PMPC‐2Chol‐II and cholesterol as a drug model formed a lamellar type of complex with an interplanar spacing of d = 35.2 Å. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1992–2000, 2003     

RAFT synthesis of polystyrene‐block‐poly(polyethylene glycol monomethyl ether acrylate) for zinc phthalocyanine‐loaded polymeric micelles as photodynamic therapy photosensitizers

A series of polystyrene‐block‐poly(polyethylene glycol monomethyl ether acrylate) (PSt_m‐b‐PPEGA_n) polymers were systematically synthesized as carriers for zinc phthalocyanine (ZnPc) for photodynamic therapy via reversible addition and fragmentation chain transfer polymerization. The degree of polymerization of the styrene (m) and PEGA units (n) of the resulting block copolymers were characterized to be n = 174, 40, and 18 for m = 52; and n = 200, 84, and 31 for m = 30. All the block copolymers formed micelles in water. The critical micelle concentration (CMC) of the PSt_m‐b‐PPEGA_n was determined by fluorometry using pyrene as a hydrophobic probe. The CMC value increased from 4.5 to 20 mg·L⁻¹ with an increase in the mole fraction of PEGA units. The median diameters of the micelles increased from 19 to 31 nm for PSt₅₂‐b‐PPEGA_n and from 15 to 23 nm for PSt₃₀‐b‐PPEGA_n with increasing n value. ZnPc‐loaded micelles were prepared by dialysis of the block copolymer in the presence of ZnPc followed by removal of large aggregates by filtration. The encapsulation efficiency was dramatically changed in the range of 0–68%. The light‐dose‐dependent cytotoxicity of the ZnPc‐loaded PSt₃₀‐b‐PPEGA₂₀₀ was clearly established in HeLa cell lines; while no cytotoxicity was confirmed under the dark. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 560–570     

Solubilization of C60 using ultrasound and amphiphilic block copolymers in acidic aqueous solutions

Fullerene (C₆₀), the third carbon allotrope, has shown great potential in photoelectric materials and drug delivery. However, the low solubility of C₆₀ in polar solvents, especially in water, is the major limiting factor for further applications. The use of ultrasound and amphiphilic block copolymers, poly(ethylene glycol)-block-poly(4-vinylpyridine) (PEG-b-P4VP), helped to disperse C₆₀ in acidic aqueous solutions. As characterized by dynamic light scattering, transmission electron microscopy, and UV-visible spectroscopy, the C₆₀ colloids had a core-shell structure with C₆₀ aggregated in the micellar cores. The photosensitized generation of singlet oxygen using C₆₀-bound polymer micelle was confirmed by the iodide method. More importantly, C₆₀ and metalloporphyrin complexes could be synthesized by the self-assembly between PEG-b-P4VP/C₆₀ micelle and metalloporphyrin. The stability of metalloporphyrin increased in the presence of the PEG-b-P4VP/C₆₀ micelle. This study provides a method for the solubilization of C₆₀ with many potential applications in biomedicals and photovoltaics.     

Hierarchically organized micellization of thermoresponsive rod‐coil copolymers based on poly[oligo(ethylene glycol) methacrylate] and poly(ε‐caprolactone)

A series of amphiphilic triblock copolymers, poly[oligo(ethylene glycol) methacrylate]_x‐block‐poly(ε‐caprolactone)‐block‐poly[oligo(ethylene glycol) methacrylate]_x, POEGMA_Co(x), were synthesized. Formation of hydrophobic domains as cores of the micelles was studied by fluorescence spectroscopy. The critical micelle concentrations in aqueous solution were found to be in the range of circa 10^?6 M. A novel methodology by modulated temperature differential scanning calorimetry was developed to determine critical micelle temperature. A significant concentration dependence of cmt was found. Dynamic light scattering measurements showed a bidispersed size distribution. The micelles showed reversible dispersion/aggregation in response to temperature cycles with lower critical solution temperature between 75 and 85 °C. The interplay of the two hydrophobic and one thermoresponsive macromolecular chains offers the chance to more complex morphologies. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Structure and properties of (1−x)(0.6Pb(Zn1/3Nb2/3)O3-0.4Pb (Mg1/3Nb2/3)O3)-xPbTiO3 thin films with perovskite phase promoted by polyethylene glycol

The preferential formation of a pyrochlore structure is a knotty problem in the preparation of Pb(Zn_1/3Nb_2/3)O₃ (PZN)-based thin film materials and its presence is significantly detrimental to the dielectric and piezoelectric properties. In this study, 40 mol% of PZN was replaced with Pb(Mg_1/3Nb_2/3)O₃ (PMN) for obtaining a perovskite composition around a morphotropic phase boundary (MPB), (1−x)(0.6PZN-0.4PMN)-xPT ((1−x)PZMN-xPT, PT: PbTiO₃) where x = 0.23. The thin films with this composition were prepared with a polyethylene glycol (PEG) modi-fied sol-gel method on LaAlO₃ substrates. The microstructural evolution of the films on heat treatment was examined with X-ray diffraction. With the aid of PEG, the formation of the pyrochlore phase was suppressed and the perovskite phase formed directly from the amorphous gel film. The multilayer films with a thickness around 0.25 μm showed a single perovskite phase without any detectable pyrochlore structure. Microscopic images showed uniform grain size of a few tens of nanometers. The role of the polymer dramatically promoting the perovskite phase was investigated with the aid of X-ray photoelectron spectroscopy and thermal analysis. The dielectric constant of the obtained film was 4160 at 1 kHz. The film demonstrated typical ferroelectric hysteresis loops and exhibited excellent piezoelectric performance.