Dynamic light scattering and cryogenic transmission electron microscopy investigations on metallo-supramolecular aqueous micelles: evidence of secondary aggregation

Metallo-supramolecular diblock copolymers consisting of a polystyrene (PS) block connected to a poly(ethylene oxide) (PEO) block by a bis(terpyridine)ruthenium complex (PS₂₀-[Ru]-PEO _y ) were used to prepare aqueous micelles. The length of the PS block was kept constant, while two PEOs of different molecular weight were used. The resulting hydrated micelles and aggregates were characterized by a combination of cryogenic transmission electron microscopy (cryo-TEM) and dynamic light scattering measurements. The results were compared to those obtained for a covalent counterpart (PS₂₂-b-PEO₇₀). Cryogenic transmission electron microscopy allowed visualization of the PS core of the micelles. Moreover, the aggregates result from clustering of individual micelles.     

Thermo-responsive block copolymers based on linear-type poly(ethylene glycol): Tunable LCST within the physiological range

Thermo-responsive block copolymers poly（ethylene glycol）-block-poly（N-acryloyl-2,2-dimethyl-1,3-oxazolidine）, PEG-b-PADMO,based on linear PEG were prepared via a versatile reversible addition-fragmentation chain transfer（RAFT） polymerization.PEG₂₂（M_w = 1000） was used as the hydrophilic component,whose dehydration was the main driving force for the phase transition of these copolymers,as demonstrated by the ¹H-NMR spectra.Their lower critical solution temperatures（LCSTs） could be tuned in the range of 20℃to 35℃,by adjusting the degree of polymerization（DP） of PADMO between 14-27.Furthermore,a sharp phase transition at ca.33℃,close to the physiological temperature with minimal hysteresis,was observed for the PEG₂₂-b-PADMO₁₄ copolymer.Moreover,excellent reversibility and reproducibility were displayed for the same copolymer over 10 cycles of repeated temperature change between 25℃（below the LCST） and 40℃（above the LCST）.     

Phase transitions and relaxation processes in ethylene-vinyl acetate copolymers probed by fluorescence spectroscopy

The steady-state fluorescence of pyrene and anthracene are used to investigate the relaxation processes of several random ethylene-co-vinyl acetate copolymers, EVA, with defined comonomer compositions (EVA-9, EVA-18, EVA-25, EVA-33 and EVA-40). The temperature of the relaxation processes are compared with those of low-density polyethylene (LDPE) and poly(vinyl acetate) (PVAc). The polymer relaxation processes are assigned to T_g=300-310 K (glass transition temperature of the PVAc); T_α=270-300 K (relaxation processes of the ethylene units present in LDPE and EVA); T_g=220-250 K (glass transition of the LDPE and of the EVA); T_γ or T_β=160-190 K (relaxation processes of interfacial defects of methylenic chains of LDPE and rotation of the acetate group of the PVAc and the EVA); and T_γ=90-130 K (relaxation processes of small sequences of methylene units of LDPE and end groups of PVAc). An Arrhenius-type function was employed as an attempt to represent the experimental data of fluorescence intensity versus temperature above the γ-relaxation temperature. As obtained with other techniques, there is not a simple relationship between the polymer relaxation processes and the vinyl acetate content that can be explained by the morphology in these copolymers.     

Dynamic light scattering and rheology studies of aqueous solutions of amphiphilic sodium maleate containing copolymers

Light scattering techniques, video particle‐tracking microrheology, and bulk rheology were employed to examine the structure and dynamics of a series of alternating sodium maleate copolymers with moderately hydrophobic comonomers (diisobutylene, styrene, and isobutylene) in aqueous solutions. The scaling dependence of the specific viscosity (η_sp) on the polyelectrolyte concentration (c) was studied with and without added salt; similar trends were found in both conventional rheology and particle‐tracking microrheology measurements, showing good performance of the technique with flexible polyelectrolytes. Furthermore, with dynamic light scattering performed in high added salt conditions, we examined the behavior of the amplitude of the fast mode, which is in agreement with scaling predictions. In contrast, the slow modes are not understood and display three separate behaviors for the wavevector q dependence of the decay rate (Γ), depending on the comonomer; superdiffusive (Γ ～ q^2.7, isobutylene) possibly because of sticky aggregates, wavevector independent (Γ ～ q⁰, styrene) most likely because of coupled polyion‐ion diffusion and diffusive (Γ ～ q^2.0, diisobutylene) presumably because these aggregates are not sticky. The hydrophobicity of the comonomer appears to switch the aggregation process between “open,” “closed,” and “non” association for isobutylene, diisobutylene, and styrene respectively. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 774–785, 2007     

Thermal characterization of tetrafluoroethylene-perfluoroalkylvinylether copolymers: Melting behavior and low-temperature transitions

Differential scanning calorimetry has been used to study the melting and the low-temperature transitions of tetrafluoroethylene-perfluoroalkylvinylether copolymers (PFA). Melting is similar to that of PTFE in that it is subject to superheating, moreover the melt-crystallized samples show temperatures and heats of fusion lower than the native ones. At temperatures lower than room temperature, crystal-crystal transitions are observed for copolymers containing 2 mol % of perfluoromethyl-, perfluoroethyl-, and perfluoro-n-propylvinylether. In the case of perfluoromethylvinylether as a comonomer, low-temperature transitions are present only up to a content of 4 mol %. The effect on melting and low-temperature transitions of both the comonomer content and of the type of side groups has been investigated. The temperatures and heats of transitions show the expected dependence as a function of the comonomer concentration and have been found to be independent on the chemical nature of the side group. © 1994 John Wiley & Sons, Inc.     

Interplay between domain microstructure and nematic order in liquid crystalline/isotropic block copolymers

The domain microstructure and the nematic LC mesophase in a series of side-chain liquid crystalline/isotropic (LC/I) diblock copolymers with systematically varied block volume fractions were studied in a broad temperature range (25–170 °C) by DSC, polarized microscopy, and wide and small angle X-ray scattering. At all temperatures the block copolymers are microphase separated. The PSLC block copolymers exhibit order at two length-scales: on one hand, a nematic LC mesophase with characteristic length-scale of 0.43 nm (intermesogen distance); on the other hand, lamellar, hexagonal or cubic domain microstructures with characteristic length-scales of 27–44 nm (lattice parameter). The LC block was either located in the matrix or confined inside the microdomains. The thermotropic behavior is characterized by the sequence g/~35 °C/n/~115 °C/i and is not affected by the domain microstructure and/or dimensions. Analysis of the lamellar dimensions showed that the LC chain is stretched. With increasing temperature, a thermal expansion of both blocks takes place followed by a retraction of the LC chain above T_NI. The phase diagram is asymmetric and does not alter above T_NI. No order-to-order transitions triggered by the nematic-isotropic transition are observed. It was shown that domain microstructures of low interfacial curvature (lamellar and hexagonal) are energetically favored over the geometrically expected ones of high interfacial curvature (micellar cubic) due to the presence of nematic LC mesophase in the matrix or in the microdomains. By comparison to theory a Kuhn segment length of the LC block b_LC=0.86 nm was derived from the location of the lamellar/hexagonal phase boundaries.This paper is dedicated to Prof. Fischer on the occasion of his 75th birthday.     

Micellization behavior of diblock and triblock copolymers of poly(t-butyl methacrylate) bearing associating short polystyrene end-blocks

Anionic polymerization high vacuum techniques were employed for the synthesis of a diblock (PS-b-PtBuMA) and two triblock (PS-b-PtBuMA-b-PS) copolymers of polystyrene (PS) and poly(t-butyl methacrylate) (PtBuMA) bearing similar low molecular weight PS end-block(s). Dilute solution viscometry, as well as static and dynamic light scattering, were employed to assess whether the short PS end-blocks were able to promote association in t-amyl alcohol, a selective solvent for PtBuMA. The effect of macromolecular architecture on the association behavior of the copolymers was also examined.     

Photoinduced optical anisotropy in azobenzene methacrylate block copolymers: Influence of molecular weight and irradiation conditions

The photoinduced anisotropy in a series of azomethacrylate block copolymers with different molecular weights and azo contents has been investigated under several irradiation conditions. Depending on molecular weight and composition, different microstructures (disordered, lamellar, spherical) appear, due to block microsegregation. Measurements of birefringence (Δn) induced with linearly polarised 488 nm light show that the highest (and stable) Δn_N values (birefringence normalised to the azo content) are achieved in copolymers with a lamellar structure. Lower Δn_N are obtained in the copolymers in which azobenzene units segregate to nano spheres and the lowest (and less stable) Δn_N values, appear in disordered systems not showing any defined microstructure. Besides, higher Δn_N is obtained in the copolymers with larger molecular weight of the poly (methyl methacrylate) and the azo polymer blocks, both in the microspheres segregated polymers as well as in those without a clear microstructure. This behaviour is consistent with that of the photoinduced order of azobenzene units obtained from dichroism measurements. Irradiation temperature (from 30 to 90 °C) and light power (from 100 to 500 mW/cm²) also influence the photoinduced response. Photoinduced Δn_N growth rate is faster when both temperature and irradiation power increase. Furthermore, birefringence is only induced at temperatures up to 90 °C, the maximum value being obtained at about 70 °C. No clear dependence of the final Δn_N value with light power has been found.     

Solubilization of hydrocarbons and resulting aggregate shape transitions in aqueous solutions of Pluronic (PEO–PPO–PEO) block copolymers

Pluronic^® block copolymers are commercially available symmetric triblock copolymers with poly(ethylene oxide), PEO, as the hydrophilic end blocks and poly(propylene oxide), PPO, as the hydrophobic middle block. In this paper, the solubilization of hydrocarbons by aggregates of Pluronic^® block copolymers in water is examined in the framework of a simple molecular theory of solubilization. The aggregates have an inner core region made up of PPO and the solubilizate and an outer corona region made up of PEO and water. Expressions for the standard state free energy change associated with solubilization of hydrocarbons by aggregates having spherical, cylindrical, and lamellar shapes are presented. These free energy contributions account for the mixing of the core block with the solubilizate, the consequent changes in the state of deformation of the core block, the changes in the state of dilution and deformation of the corona block, the formation of the core-solvent interface, and the backfolding of the triblock copolymer which ensures that the two end blocks are in contact with the solvent. Utilizing these free energy expressions, we predict the core size, the corona thickness, and the aggregation number of the micelle and also the volume fraction of the hydrocarbon solubilized in the core, for seven aromatic and aliphatic hydrocarbon solubilizates incorporated within numerous Pluronic^® compounds. The calculated results show that a growth in aggregate size occurs both because of the incorporation of the hydrocarbon and also the increase in the intrinsic number of block copolymer molecules per aggregate. More interestingly, solubilization is shown to induce a transition in aggregate shapes from spheres to cylinders and then to lamellae. The shape transition is found to be critically controlled by the free energy of mixing of the solubilizate with the core forming PPO block.     

Super-nucleation in nanocomposites and confinement effects on the crystallizable components within block copolymers, miktoarm star copolymers and nanocomposites

In this paper we reexamine recent results obtained by our group on the crystallization of nanocomposites and linear and miktoarm star copolymers in order to obtain some general features of their crystallization properties. Different nanocomposites have been prepared where a close interaction between the polymer matrix and the nano-filler has been achieved: in situ polymerized high density polyethylene (HDPE) on carbon nanotubes (CNT); and polycaprolactone (PCL) and poly(ethylene oxide) (PEO) covalently bonded to carbon nanotubes. In all these nanocomposites a “super-nucleation” effect was detected where the CNTs perform a more efficient nucleating action than the self-nuclei of the polymer matrix. It is believed that such a super-nucleation effect stems from the fact that the polymer chains are tethered to the surface of the CNT and can easily form nuclei. For polystyrene (PS) and PCL block copolymers, miktoarm star copolymers (with two arms of PS and two arms of PCL) were found to display more compact morphologies for equivalent compositions than linear PS-b-PCL diblock copolymers. As a consequence, the crystallization of the PCL component always experienced much higher confinement in the miktoarm stars case than in the linear diblock copolymer case. The consequences of the topological confinement of the chains in block copolymers and nanocomposites on the crystallization were the same even though the origin of the effect is different in each case. For nanocomposites a competition between super-nucleation and confinement was detected and the behavior was dominated by one or the other depending on the nano-filler content. At low contents the super-nucleation effect dominates. In both cases, the confinement increases as the nano-filler content increases or the second block content increases (in this case a non-crystallizable block such as PS). The consequences of confinement are: a reduction of both crystallization and melting temperatures, a strong reduction of the crystallinity degree, an increase in the supercooling needed for isothermal crystallization, a depression of the overall crystallization rate and a decrease in the Avrami index until values of one or lower are achieved indicating a nucleation control on the overall crystallization kinetics.     

Concentrated reverse micelles in a random graft block copolymer system: structure and in-situ synthesis of silver nanoparticles

The structure and rheological properties of a poly(dimethylsiloxane)-graft-poly(oxyethylene) copolymer at high concentrations in block-selective solvents were studied by small-angle X-ray scattering (SAXS) and rheometry. Analysis of SAXS data indicates that quasispherical, reverse micellar aggregates (with no ordered packing) are present in concentrated solutions of the copolymer in nonpolar solvents, and that upon addition of water, the size of such aggregates increases due to the solubilization inside the micellar cores. The viscosity of concentrated polymer solutions increases exponentially as water is added, and finally, viscoelastic, gel-like behavior is found in the vicinity of the phase separation limit. It was found that small silver nanoparticles with an average diameter of ≈3 nm can be synthesized inside the copolymer aggregates without the need of a reducing agent; namely, particles embedded in a viscoelastic matrix are obtained. The synthesis seems to follow first-order kinetics. Electronic supplementary material Supplementary material is available in the online version of this article at and is accessible for authorized users.     

环境响应性嵌段共聚物的合成、自组装及应用研究进展

近年来具有环境响应性的嵌段共聚物的研发受到了人们的广泛关注。该类型共聚物可以对外界环境刺激产生相应的结构、物理及化学性能的变化。根据外界环境刺激响应机理及类型的不同,可将其分为单一因素、双重因素以及三重因素刺激响应性嵌段共聚物三大类。针对每一类体系,本文重点综述了嵌段共聚物的设计合成、自组装以及应用等研究现状,并概括总结了各种有序聚集体(如胶束、囊泡等)随外界环境刺激(如pH、温度、光、CO_2、氧化还原剂等)所作出的响应性变化。最后,对智能型嵌段共聚物在药物控释、纳米容器制备、生物功能材料等方面潜在的应用价值和今后可能的发展方向进行了展望。     

Amphiphilic maleic acid-containing alternating copolymers—2. Dilute solution characterization by light scattering,intrinsic viscosity,and PGSE NMR spectroscopy

The dilute solution behavior of several alternating copolymers of maleic acid has been characterized by static and dynamic light scattering, intrinsic viscosity, and pulsed-gradient spin-echo NMR spectroscopy. The copolymer of maleic acid–sodium salt and isobutylene (IBMA-Na, M_w ∼350 kg/mol) dissolves readily in concentrated aqueous salt solutions. Changes in chain dimensions with ionic strength and pH are similar to those of the lesser salt solution-soluble poly(acrylic acid-sodium salt). The hydrophobically modified (with n-butyl, n-hexyl, n-octyl, and phenethyl amines) copolymers of maleic acid–sodium salts and isobutylene (IBMA-NHR-Na) show no sign of large intermolecular aggregation in 0.1 N sodium acetate (NaAc). However, the sizes of the copolymers are relatively small compared to that of the ionized parent copolymer (IBMA-Na, M_w ∼350 kg/mol), suggesting intramolecular aggregation of the alkyl side-chain groups along the polymer backbone. The copolymer modified with the longer chain n-decyl, on the other hand, forms stable large intermolecular aggregates containing 33 chains/aggregate. The copolymers of maleic acid–sodium salt and styrene (SMA-Na) appear to have no signs of aggregation, despite being a hydrophobic polyelectrolyte. The copolymer of maleic acid–sodium salt and di-isobutylene (DIBMA-Na) has a similar salting-out concentration as SMA-Na. The radius of gyration measurements by static light scattering suggest that at least some fraction of the DIBMA-Na chains form large intermolecular aggregates. The copolymers of maleic acid–sodium salt with n-alkenes (n-C_mMA-Na) in 0.1 N NaAc form small intermolecular aggregates (three to five chains/aggregate). In contrast to these static light scattering results, PGSE NMR diffusion measurements for the above aggregated systems indicate only one diffusion coefficient consistent with the motion of single isolated chains. A plausible explanation for this discrepancy is that the population of the aggregates is too small to be sufficiently detected in the PGSE NMR experiment. Furthermore, it is likely that the aggregate has a larger relaxation rate than the nonaggregate, and therefore has a comparatively reduced signal in the PGSE NMR experiment. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3584–3597, 2004     

PLMA‐b‐POEGMA amphiphilic block copolymers: Synthesis and self‐assembly in aqueous media

The synthesis and self‐assembly properties in aqueous solutions of novel amphiphilic block copolymers composed of one hydrophobic poly (lauryl methacrylate), (PLMA) block and one hydrophilic poly (oligo ethylene glycol methacrylate) (POEGMA) block are reported. The block copolymers were prepared by RAFT polymerization and were molecularly characterized by size exclusion chromatography, NMR and FT‐IR spectroscopy, and DSC. The PLMA‐b‐POEGMA amphiphilic block copolymers self‐assemble in nanosized complex nanostructures resembling compound micelles when inserted in aqueous media, as supported by light scattering and TEM measurements. The encapsulation and release of the model, hydrophobic, nonsteroidal anti‐inflammatory drug indomethacin in the polymeric micelles is also investigated. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 155–163     

The advantages of evaporative light scattering detection in pharmaceutical analysis by high performance liquid chromatography and supercritical fluid chromatography

The evaporative light scattering detector (ELSD) has been used in pharmaceutical analysis by liquid and supercritical fluid chromatography. An ELSD equipped with interchangeable interfaces enables the use of various eluents (UV- or non-UV-absorbing) in isocratic or gradient mode. Analyses were performed on several non-UV-absorbing excipients and active substances. The narrow spread of the response factors of the various compounds investigated has indicated that the detector is suitable for direct raw quantitation of unknown samples in stability studies.     

Dynamic light scattering from asymmetric block copolymers in neutral good solvents: Evidence of association in the disordered state

Dynamic light scattering (DLS) has been used to explore the properties of asymmetric styrene-isoprene (SI) block copolymers in concentrated solutions. Concentrations were always well below those necessary to access the order–disorder transition in neutral good solvents. The samples include SI (10-50), SI (36-9), and SIS (10-100-10), where the numerical suffixes denote the block molecular weights in kilodaltons; experimental emphasis was placed on SI (10-50). The DLS intensity correlation functions in the neutral good solvents, THF and toluene, were dominated by a slow mode that first appeared at a concentration c⁺ ≈ 4 c*, where c* is the coil overlap concentration. The decay rate of this mode scaled approximately as the third power of the scattering wavevector, and the excess scattered intensity decreased with increased scattering angle. These results were tentatively ascribed to the onset of substantial concentration fluctuations, that exhibited cylindrical, or wormlike structures. Measurements in solvents of known selectivity, dioxane and cyclohexane, and on a copolymer of the opposite composition, SI (36-9), indicated that the intermolecular association was driven by the effectively repulsive interactions between styrene and isoprene segments, rather than by solvent selectivity. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 1831–1837, 1998     

Synthesis,dynamic light scattering,and luminescence properties of copolymers containing iridium(III) bisterpyridine in the side chain

Supramolecular block‐random copolymers containing [Ir(terpy)₂]³⁺ in the side chain were synthesized via postfunctionalization of a P(S‐b‐AC_terpy) block copolymer. Absorbance and emission spectra compared to a model compound show that the polymer backbone has a minor effect on the polymer absorbance but produces a larger shift for the phosphorescence signals to higher wavelength. Dynamic light scattering of the metal complex containing copolymer studied in various solvents showed monomodal aggregation with decreasing aggregate size as the solvent dielectric constant increased. The copolymer precursor P(S‐b‐AC_terpy) shows multimodal aggregation in different solvents with the major population consisting of single chains. This difference in behavior between the two polymers is attributed to the electrolytic nature of the complex and the amphiphilicity induced by the charged metal complex. Supramolecular copolymers like these will continue to have interesting self‐organizational properties and may find applications in multicomponent systems for photoinduced charge separation processes. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1109–1121, 2007     

The solubilisation behaviour of some dichloroalkanes in aqueous solutions of PEO-PPO-PEO triblock copolymers: a dynamic light scattering, fluorescence spectroscopy, and SANS study

The aggregation behaviour of PEO-PPO-PEO triblock copolymers in water and in water + chlorinated additive mixtures was studied by means of fluorescence spectroscopy, dynamic light scattering (DLS), and small-angle neutron scattering (SANS). The copolymers were chosen such as to investigate the effects of molecular architecture (L35 and 10R5) and molecular weight by keeping constant the hydrophilic/hydrophobic balance (F88 and F108). 1,2-Dichloroethane was used as a prototype of water basins contaminants. The hydrodynamic radius of the block copolymer aggregates (R(h,M)) and the intensity ratio of pyrene of the first and the third vibrational band (I(1)/I(3)) were determined as a function of temperature (10-45 degrees C) and concentration. The copolymer architecture essentially does not affect R(h,M) in the entire range of temperature and concentration investigated. At a given temperature, increasing macromolecular size leads to a decrease of R(h,M). With rising temperature R(h,M) also decreases. According to the DLS results, the I(1)/I(3) change with temperature clearly detects the aggregation only for F88 and F108. The presence of 1,2-dichloroethane, at concentrations close to its solubility in water, does not lead to changes in the distribution of hydrodynamic radii for L35 and 10R5. Larger quantities of additive induce the formation of quite polydisperse mixed aggregates for L35 and of networks for 10R5. In the case of F88 and F108, low concentrations of additive lead to formation of mixed aggregates with smaller R(h,M). The SANS results corroborate the DLS and fluorescence findings proving enhancement of the copolymer aggregation through the presence of 1,2-dichloroethane. The DLS findings combined with those from the fluorescence spectroscopy provide some insight into the site of solubilisation of the additive in the aggregates.     

Raman scattering investigation with temperature of the phase transitions in (Pb0.825Ba0.175)ZrO3 and (Pb0.65Ba0.35)ZrO3 ceramics

Raman scattering investigations of lead-barium zirconate are presented for two barium concentrations, as a function of temperature from 10 to 450 K. An order-disorder phase transition is observed at 130 K for the low barium concentration, for which an antiferroelectric-ferroelectric phase transition is equally observed at 308 K and a ferroelectric-paraelectric one at 433 K. The ceramic containing a high barium concentration is in a ferroelectric state up to 403 K, above this temperature begins the paraelectric phase of the material. The order parameters of the two types of transitions, order-disorder and antiferroelectric-ferroelectric, are evaluated.