Preparation and properties of azobenzene-containing amphiphilic miktoarm star polymers

Summary A series of novel miktoarm star polymers composed of a poly(ethylene oxide) (PEO) and two side-chain liquid crystalline azobenzene-containing polymethacrylate (PEO-(PMMAZO)₂) were prepared using atom transfer radical polymerization (ATRP). Bifunctional macroinitiator PEO-Br₂ was synthesized by condensation reaction in two steps and characterized by ¹H NMR, ¹³C NMR and IR. Kinetic study showed that it was a first order reaction referred to the monomer MMAZO, namely, 6-(4-methoxy-4’-oxy-azobenzene)hexyl methacrylate. The liquid crystalline behaviors of the miktoarm star polymers were studied by differential scanning calorimetry (DSC) and polarized optical microscope (POM). They exhibited smectic and nematic mesophases when Mn was beyond 9.4×10³ g/mol. The phase transition temperatures of the smectic and nematic phases increased while the melting temperature of PEO decreased with increasing molecular weight of the LC block. Compared with diblock polymer PEO-PMMAZO, the melting temperature of PEO in miktoarm star polymer decreased more rapidly.     

Step-scan alternating DSC study of melting and crystallisation in poly(ethylene oxide)

Step-scan alternating differential scanning calorimetry (SSA-DSC) method was applied to investigate the phase behaviour of well-characterised poly(ethylene oxide) (PEO). Influence of the three main measurement's parameters of SSA-DSC method: length of the isothermal segment (t_iso/s), temperature jump between two subsequent isothermal segments (step/deg) and linear heating rate in dynamic segments (b/K/min), on the shape of reversing and non-reversing components during the melting and crystallisation of PEO, has been evaluated. It was found that the reversing component during melting of PEO is increasing with an increase of the isothermal segment length. This effect is due to the existence of defected polymer crystal structures that form metastable regions between crystal phase and already melted polymer. Reversible recrystallisation in the presence of still existing polymer crystals is facilitated by longer isothermal segments. By increasing the step, the equilibrium of reversible processes is shifted towards products and activation of rate-controlled processes takes place; molecular nucleation is hampered and partial melting and/or recrystallisation proceed slower—this effect can be observed as a decrease of reversing signal with increasing step.     

Crystallization behavior of PEO in blends of poly(ethylene oxide)/poly(2‐vinyl pyridine)‐b‐(ethylene oxide) block copolymer

The crystallization behavior of two molecular weight poly(ethylene oxide)s (PEO) and their blends with the block copolymer poly(2‐vinyl pyridine)‐b‐poly(ethylene oxide) (P2VP‐b‐PEO) was investigated by polarized optical microscopy, thermogravimetric analysis, differential scanning calorimetry, and atomic force microscopy (AFM). A sharp decreasing of the spherulite growth rate was observed with the increasing of the copolymer content in the blend. The addition of P2VP‐b‐PEO to PEO increases the degradation temperature becoming the thermal stability of the blend very similar to that of the block copolymer P2VP‐b‐PEO. Glass transition temperatures, T_g, for PEO/P2VP‐b‐PEO blends were intermediate between those of the pure components and the value increased as the content of PEO homopolymer decreased in the blend. AFM images showed spherulites with lamellar crystal morphology for the homopolymer PEO. Lamellar crystal morphology with sheaf‐like lamellar arrangement was observed for 80 wt% PEO(200M) and a lamellar crystal morphology with grain aggregation was observed for 50 and 20 wt% blends. The isothermal crystallization kinetics of PEO was progressively retarded as the copolymer content in the blend increased, since the copolymer hinders the molecular mobility in the miscible amorphous phase. POLYM. ENG. SCI., 2012. © 2011 Society of Plastics Engineers     

Ionomeric blends of poly(ethylene oxide) with poly(styrene‐co‐maleic anhydride) ionomer: Miscibility,crystallization, and melting behavior

The miscibility and crystallization behavior of poly(ethylene oxide) (PEO) and poly(styrene‐co‐maleic anhydride) ionomer (SMAI) blends were studied by the dynamic mechanical analysis (DMA) and differential scanning calorimetry (DSC). This study has demonstrated that the presence of ion–dipole interactions enhances the miscibility of otherwise immiscible polymers in the PEO and high molecular weight poly(styrene‐co‐maleic anhydride) (SMA). The effect of ion–dipole interactions on enhancing miscibility is confirmed by the presence of a single glass transition temperature (T_g) and a depression of the equilibrium melting temperature of the PEO component. The equilibrium melting temperature of PEO in the blends are obtained using Hoffman‐Weeks plots. The interaction energy density, β, is calculated from these data using the Nishi‐Wang equation. The results suggest that PEO and SMAI blends are thermodynamically miscible in the melt. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1–7, 2000     

On the thermodynamics of solid solutions of polymer and salt

Solid solutions of poly(ethylene oxide) of different molecular masses (M_η from 6 × 10⁵ to 4 × 10⁶ g mol^?1) and lithium perchlorate (LiClO₄) were prepared by solution casting method. Salt concentrations of solutions vary between around 2 and 13 wt%. Thermodynamic properties of these solutions are reported in the range of low salt content. The solutions represent two‐phase systems mostly not in equilibrium at room temperature. They consist of neat crystalline PEO and an amorphous mixture of salt and polymer. Crystallinity of PEO in salt solutions stays constant with increasing salt content and is independent of molecular mass. Crystallinities serve determining share and composition of the amorphous phase. Glass transition temperature increases linearly with salt content in the amorphous phase. Depression of equilibrium melting points by addition of salt provides activity coefficients in solutions and allows for estimation of degrees of dissociation. Rate of crystallization of poly(ethylene oxide) depends exponentially on inverse undercooling. In that way, it is also coined by equilibrium melting point depression. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers     

Morphology evolution in superheated crystal monolayer of low molecular weight poly(ethylene oxide) on mica surface

Using atomic force microscopy (AFM) coupled with a hot stage, we studied the morphological evolution of superheated poly(ethylene oxide) (PEO) crystal monolayer on the mica surface. The PEO possesses a number average molecular weight (M_n) of 4250 g/mol and a polydispersity of 1.03. The superheated monolayer was obtained when the entire periphery of a triply-folded chain crystal [IF(3)] was thickened to be a twice-folded chain crystal [IF(2)] ‘dam’. The IF(3) crystal was laterally confined by the IF(2) ‘dam’ and remained unchanged at its unconfined melting temperature (T_m). In superheated conditions, the interior IF(3) crystal unfolded, resulting in domains with a thickness in between the fold lengths of the IF(3) and the IF(2) crystals accompanied by hole formation. After its nucleation, the hole enlarged its area quickly and migrated long distances within the area bounded by the IF(2) crystal ‘dam’.     

Butyllithium-initiated anionic synthesis of well-defined poly(styrene-block-ethylene oxide) block copolymers with potassium salt additives

Poly(styrene-block-ethylene oxide) (PS–PEO) diblock copolymers have been synthesized with predictable block molecular weights and narrow molecular weight distributions. sec-Butyllithium-initiated polymerization of styrene was effected in benzene solution followed by ω-end-group functionalization with ethylene oxide to form the corresponding polymeric lithium alkoxide (PSOLi). Block copolymerization of ethylene oxide initiated by the unreactive PSOLi was promoted by addition of dimethylsulfoxide and either potassium t-butoxide, potassium t-amyloxide or potassium 2,6-di-t-butylphenoxide. Although the PS–PEO block copolymer product contained some poly(ethylene oxide) homopolymer, the poly(ethylene oxide) block M̄_n was in good agreement with the calculated value and the molecular weight distribution of the final block was generally narrow (M̄_w/M̄_n ≤ 1.1). The amount of PEO homopolymer was minimized using potassium 2,6-di-t-butylphenoxide rather than potassium t-alkoxides.     

Nanoheterogeneities in PEO/PMMA blends: A modulated differential scanning calorimetry approach

Modulated differential scanning calorimetry has been carried out on melt‐mixed blends of poly(ethylene oxide)/atactic‐poly(methyl methacrylate) (PEO/PMMA). Two PEO molecular weights have been used to prepare blends in the concentration range 10 to 80 wt % of PEO. Two glass transitions temperatures were observed for the fully amorphous blends, in the 10 to 30 wt % PEO range, using the differential of heat capacity with respect to temperature [dC_p/dT] signal. The semicrystalline blends, 40, 60, and 80 wt % PEO, exhibited melting of PEO crystallites and the PEO‐rich phase glass transition at −30 to −50°C. A second glass transition around 30°C was detected for the 40 wt % PEO blend when a cooling run was carried out, because PEO crystallization was avoided under these conditions. Therefore, heterogeneous amorphous phases were observed not only for fully amorphous blends, but also for semicrystalline ones. Further analysis of the dC_p/dT signal, obtained from the MTDSC experiments by fitting with Gaussian curves, showed that there is an interphase that varies in amount between 10 to 50 wt %. Correlation of the MTDSC observations with NMR spectroscopy and SAXS/SANS literature results are discussed. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 2034–2043, 2000     

Effect of annealing‐induced interfacial demixing on crystallization of PEO confined in coaxial electrospun nanofibers

Glassy polymer nanofibers with spatially confined poly(ethylene oxide) (PEO) were fabricated by coaxial electrospinning of PEO with polyacrylonitrile (PAN) or polystyrene. The effect of melt‐annealing on the crystallization behavior of the confined PEOs was studied using differential scanning calorimetry. It is found that the crystallization behavior of the confined PEOs varies with annealing temperature (T_a), annealing time (t_a), and molecular weight of PEO. Notably, it is observed that the crystallization temperature (T_c) and melting temperature (T_m) of PEO increase with prolongation of t_a, for PEO600K/PAN and PEO2K/PAN coaxial electrospun fibers. This phenomenon can be interpreted by the annealing‐induced demixing at the core‐sheath interface. After the coaxial electrospinning, the core and sheath of the PEO/PAN coaxial fibers are partially compatible due to the miscible solvents used for the core and sheath polymers. Upon annealing, demixing occurs at the core‐sheath interface, leading to improved crystallizability of PEO. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45760.     

Porous biodegradable polyesters. I. Preparation of porous poly(L‐lactide) films by extraction of poly(ethylene oxide) from their blends

Porous poly(L ‐lactide) (PLLA) films were prepared by water extraction of poly(ethylene oxide) (PEO) from solution‐cast PLLA and PEO blend films. The dependence of blend ratio and molecular weight of PEO on the porosity and pore size of films was investigated by gravimetry and scanning electron microscopy. The film porosity and extracted weight ratio were in good agreement with the expected for porous films prepared using PEO of low molecular weight (M_w = 1 × 10³), but shifted to lower values than expected when high molecular weight PEO (M_w = 1 × 10⁵) was utilized. The maximum pore size was larger for porous films prepared from PEO having higher molecular weight, when compared at the same blending ratio of PLLA and PEO before water extraction. Differential scanning calorimetry of as‐cast PLLA and PEO blend films revealed that PLLA and PEO were phase‐separated at least after solvent evaporation. On the other hand, comparison of blend films before and after extraction suggested that a small amount of PEO was trapped in the amorphous region between PLLA crystallites even after water extraction and hindered PLLA crystallization during solvent evaporation. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 629–637, 2000     

Phase behaviors of polymer blend(PEO–PPO) electrolyte/LiCF3SO3 systems in lithium battery

Polymer blend (poly(ethylene oxide) (PEO)–poly(propylene oxide) (PPO)) systems with two different mole ratios, complexed with LiCF₃SO₃ salt, have been characterized at various temperatures and compositions using a thermo‐optical analysis (TOA) technique. We also developed a new melting point depression theory based on the modified perturbed hard sphere chain model to interpret phase behavior of polymer blend electrolyte systems. The obtained results show that the eutectic points move toward higher T_m and lower weight fraction of salt with decreasing PEO mole ratio and also indicate that the mole ratio of PEO–PPO for each polymer blend plays an important role in determining the eutectic point of the polymer blend system. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 2314–2319, 2005     

Compatibilizing effects of poly(styrene-graft-ethylene oxide) in blends of polystyrene and butyl acrylate polymers

The compatibilizing effect of poly(styrene-graft-ethylene oxide) in polystyrene (PS) blends with poly(n-butyl acrylate) (PBA) and poly(n-butyl acrylate-co-acrylic acid) (PBAAA) was investigated. No significant effects of the graft copolymer on the domain size were found in the PBA blends. By functionalizing PBA with acrylic acid, the average size of the polyacrylate domains was reduced considerably by the graft copolymer. Thermal and dynamic mechanical analysis of the PS/PBAAA blends revealed that the PBAAA glass transition temperature (T_g) decreased with increasing graft copolymer content. The effect of the graft copolymer in the PS/PBAAA blends can be explained by interactions across the interface due to the formation of hydrogen bonds between the poly(ethylene oxide) (PEO) side chains in the graft copolymer and the acrylic acid segments in the PBAAA phase. Hydrogen bonding was confirmed by IR analysis of binary blends of PEO and PBAAA. Partial miscibility in the PEO/PBAAA blends was indicated by a PEO melting point depression and by a T_g reduction of the PBAAA phase. The thermal properties of the PEO/PBA blends indicated only very limited miscibility. © 1996 John Wiley & Sons, Inc.     

Synthesis and properties of hydrophilic segmented block copolymers based on poly(ethylene oxide)‐ran‐poly(propylene oxide)

The present article discusses the synthesis and various properties of segmented block copolymers with random copolymer segments of poly(ethylene oxide) and poly(propylene oxide) (PEO‐r‐PPO) together with monodisperse amide segments. The PEO‐r‐PPO contained 25 wt % PPO units and the segment presented a molecular weight of 2500 g/mol. The synthesized copolymers were analyzed by differential scanning calorimetry, Fourier transform infra‐red spectroscopy, atomic force microscopy and dynamic mechanical thermal analysis. In addition, the hydrophilicity and the contact angles (CAs) were studied. The PEO‐r‐PPO segments displayed a single low glass transition temperature, as well as a low PEO crystallinity and melting temperature, which gave enhanced low‐temperature properties of the copolymer. The water absorption values remained high. In comparison to mixtures of PEO/PPO segments, the random dispersion of PPO units in the PEO segments was more effective in reducing the PEO crystallinity and melting temperature, without affecting the hydrophilicity. Increasing the polyether segment length with terephthalic groups from 2500 to 10,000 g/mol increased the hydrophilicity and the room temperature elasticity. Furthermore, the CAs were found to be low 22–39° and changed with the crosslink density. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci 117:1394–1404, 2010     

PBT-b-PEO-b-PBT triblock copolymers: Synthesis,characterization and double-crystalline properties

We demonstrated here a facile method to synthesize novel double crystalline poly(butylene terephthalate)-block-poly(ethylene oxide)-block-poly(butylene terephthalate) (PBT-b-PEO-b-PBT) triblock copolymers by solution ring-opening polymerization (ROP) of cyclic oligo(butylene terephthalate)s (COBTs) using poly(ethylene glycol) (PEG) as macroinitiator and titanium isopropyloxide as catalyst. The structure of copolymers was well characterized by ¹H NMR and GPC. TGA results revealed that the decomposition temperature of PEO in triblock copolymers increased about 30 °C to the same as PBT copolymers, after being end-capped with PBT polymers. These triblock copolymers showed double crystalline properties from PBT and PEO blocks, observed from DSC and WAXD measurements. The melting and crystallization peak temperatures corresponding to PBT blocks increased with PBT content. The crystallization of PBT blocks showed the strong confinement effects on PEO blocks due to covalent linking of PBT blocks with PEO blocks, where the melting and crystallization temperatures and crystallinity corresponding to PEO blocks decreased significantly with increment of PBT content. The confinement effect was also observed by SAXS experiments, where the long distance order between lamella crystals decreases with increasing PBT length. For the triblock copolymer with highest PBT content (PBT₅₄-b-PEO₂₂₇-b-PBT₅₄), this effect shows a 30 °C depression on PEO crystals' melting temperature and 77% on enthalpy, respectively, compared to corresponding PEO homopolymer. The crystal morphology was observed by POM, and amorphous-like spherulites were observed during PBT crystallization.     

Correlation between interactions, miscibility, and spherulite growth in crystalline/crystalline blends of poly(ethylene oxide) and polyesters

Crystalline/crystalline blend systems of poly(ethylene oxide) (PEO) and a homologous series of polyesters, from poly(ethylene adipate) to poly(hexamethylene sebacate), of different CH₂/CO ratios (from 3.0 to 7.0) were examined. Correlation between interactions, miscibility, and spherulite growth rate was discussed. Owing to proximity of blend constituents' T_g's, the miscibility in the crystalline/crystalline blends was mainly justified by thermodynamic and kinetic evidence extracted from characterization of the PEO crystals grown from mixtures of PEO and polyesters at melt state. By overcoming experimental difficulty in assessing the phase behavior of two crystalline polymers with closely spaced T_g's, this work has further extended the range of polyesters that can be miscible with PEO. The interaction parameters (χ₁₂) for miscible blends of PEO with polyesters [poly(ethylene adipate), poly(propylene adipate), poly(butylene adipate), and poly(ethylene azelate) with CH₂/CO = 3.0-4.5] are all negative but the values vary with the polyester structures, with a maximum for the blend of PEO/poly(propylene adipate) (CH₂/CO = 3.5). The values of interactions are apparently dependent on the structures of the polyester constituent in the blends; interaction strength for the miscible PEO/polyester systems correlate in the same trend with the PEO crystal growth rates in the blends.     

Aqueous reactive polyurethane prepolymer with poly(ethylene oxide) monomethyl ether side chains for the hydrophilic finishing of poly(ethylene terephthalate) fabrics

In this study, a series of aqueous polyurethane (PU) prepolymers were synthesized with 4,4‐methylene bis(isocyanatocyclohexane), poly(ethylene glycol) or polycaprolactone diol (PCL), methyl ethyl ketoxime, and dispersing centers produced by isophorone diisocyanate, N‐diethanol amine, and poly(ethylene oxide) monomethyl ether (PEO), containing different hydrophobic groups (? CH₃ and ? C₆H₄C₉H₁₉) at the end. The thermal properties of the prepolymers and the characteristics of poly(ethylene terephthalate) (PET)‐treated fabrics were investigated. The glass‐transition temperature was the highest in the CC prepolymer containing a benzene ring (? C₆H₄C₉H₁₉) and a long PEO side chain, and it was the lowest in the CA prepolymer having a longer PEO side chain. The CB prepolymer containing a shorter PEO side chain did not produce a melting point of PEO, although a heat endothermic peak of the PCL crystal appeared. The melting point and enthalpy from PEO of the CA prepolymer were larger than those of the CC prepolymer. With respect to the hydrophilic finishing effects of aqueous PU prepolymers for PET fabrics, the fabric treated with the CB prepolymer had higher add‐on and washing durability than the fabrics treated with the CA prepolymer, which was followed by the CC prepolymer with the lowest, but the opposite trend was found for the hydrophilic properties. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Preparation and characterization of amphiphilic block copolymer of polyacrylonitrile‐block‐poly(ethylene oxide)

The synthesis of polyacrylonitrile‐block‐poly(ethylene oxide) (PAN‐b‐PEO) diblock copolymers is conducted by sequential initiation and Ce(IV) redox polymerization using amino‐alcohol as the parent compound. In the first step, amino‐alcohol potassium with a protected amine group initiates the polymerization of ethylene oxide (EO) to yield poly(ethylene oxide) (PEO) with an amine end group (PEO‐NH₂), which is used to synthesize a PAN‐b‐PEO diblock copolymer with Ce(IV) that takes place in the redox initiation system. A PAN‐poly(ethylene glycol)‐PAN (PAN‐PEG‐PAN) triblock copolymer is prepared by the same redox system consisting of ceric ions and PEG in an aqueous medium. The structure of the copolymer is characterized in detail by GPC, IR, ¹H‐NMR, DSC, and X‐ray diffraction. The propagation of the PAN chain is dependent on the molecular weight and concentration of the PEO prepolymer. The crystallization of the PAN and PEO block is discussed. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1753–1759, 2003     

Crystal structure of the poly(ethylene oxide)–p-nitrophenol molecular complex

A crystalline complex of poly(ethylene oxide) (PEO) and p-nitrophenol (PNP) was studied by differential scanning calorimetry, X-ray diffraction, and FTIR spectroscopy, The phase diagram of this system is characterized by a peritectic reaction, and reveals the formation of a new crystal form different from those of PEO, and PNP. The triclinic unit cell of the complex was determined from the X-ray diffraction patterns of differently oriented samples obtained by mechanical deformations or spherulitic crystallizations. Finally, the molecular packing and the conformation adopted by the PEO chains were determined by FTIR spectroscopy. Polarization measurements have shown that the aromatic rings are very nearly normal to the c parameter (chain axis) and that the 1–4 axes of PNP molecules are parallel to the a^* reciprocal parameter (spherulitic growth direction). Finally, a new (t₂ gt₂ gt₃) conformation is proposed for the PEO chains on the basis of a normal mode analysis and the calculation of the intramolecular energy.     

Eutectic‐forming binary system of poly(ethylene oxide) and p‐hydroxybenzaldehyde

The binary system consisting of poly(ethylene oxide) (PEO) and p‐hydroxybenzaldehyde (PHD) was characterized with the aid of differential scanning calorimetry, polarized optical microscopy, scanning electron microscopy and Fourier‐transform infrared spectroscopy. The phase diagram created from thermal analysis data provides clear evidence for the presence of a eutectic at 35.5 °C and PHD weight fraction of 42%. Microscopy studies show that, for the mixtures with a PHD weight fraction below 42%, the resulting morphology of the crystallized sample is coarse spherulitic texture. In the case of eutectic composition, the crystallization of the binary melt produces degenerated homogenous spherulites. For the hypoeutectic PEO–PHD mixtures, the PHD crystals become large and thick with decreasing the PEO fraction. Moreover, the infrared measurements indicate that hydrogen bonding in the PEO–PHD binary system has an important effect on the PEO helical conformation. With increase of the amount of PHD component, the PEO helical conformation in the PEO–PHD mixtures changes from the 7₂ helix to the 10₃ helix. Further increase of the PHD content leads to the destruction of the PEO helical conformation. Copyright © 2003 Society of Chemical Industry     

On the deformation of poly(methyl methacrylate) poly(ethylene oxide) blends: A molecular characterization by small-angle neutron scattering

The deformation behavior of miscible amorphous/amorphous PMMA/PEO poly(methyl methacrylate)/poly(ethylene oxide) blends was compared with that of pure PMMA. Small-angle neutron scattering experiments were performed on labeled systems made of PEO + D-PMMA + HPMMA. Characteristic molecular parameters such as radius of gyration, Rg, molecular weight, M_w, and interaction parameter, X, were extracted from the coherent scattering cross sections, Molecular anisotropy was measured on the solid state coextruded samples, and the observed drawing efficiency is compared with, the results of shrinkage tests. In the case of PMMA/PEO blends, anomalous scattering behavior precludes any quantitative Interpretation of the scattering patterns, but revealed important structural changes upon drawing, namely a deformation-induced phase separation.