Viscoelastic behavior and order-disorder transition in mixtures of a block copolymer and a midblock-associating resin

The viscoelastic behavior and order-disorder transition in mixtures of a block copolymer and a midblock-associating resin were investigated. The block copolymers investigated were polystyrene-block-polysioprene-block-polystyrene (SIS) copolymers (Shell Development Company), specifically Kraton D-1107, with the block molecular weights 10,000S-120,000I-10,000S, and Kraton D-1111, with the block molecular weights 15,000S-100,000I-15,000S. The midblock-associating resin investigated was a resin polymerized from C₅ hydrocarbon, referred to as Piccotac 95BHT (Hercules Inc.), which is an aliphatic hydrocarbon containing considerable amounts of cyclic structures, with a weight-average molecular weight of 1,100 and a glass transition temperature T_g of 43°C. In the investigation, mixtures of the block copolymer and Piccotac 95BHT were prepared with toluene as solvent. Temperature scans of the samples were made to obtain information on dynamic storage modulus G′, dynamic loss modulus G″, and loss tangent tan δ, using a Rheometrics dynamic mechanical spectrometer. It was found that Piccotac 95BHT decreased the plateau modulus G⁰_N and increased the T_g of the polyisoprene midblock of the SIS block copolymer in the mixture. This experimental observation led to the conclusion that Piccotac 95BHT associates (or is compatible) with the rubbery polyisoprene midblock of the SIS block copolymer. The order-disorder transition behavior of mixtures of SIS block copolymer and Piccotac 95BHT was also investigated by a rheological technique proposed by Han and Kim (Ref. 21). The order-disorder transition temperature T_r (i.e., the temperature at which the ordered microdomain structure of the block copolymer completely disappears) of the SIS block copolymer decreased steadily with increasing amount of Piccotac 95BHT in the mixture. With the information determined on T_r, a phase diagram for the mixture was constructed, showing the boundary between the mesophase and homogeneous phase in the mixture. The phase diagram is in qualitative agreement with the theoretical predictions of Whitmore and Noolandi (Ref. 28).     

Block copolymer compatibilizers for polystyrene/poly(dimethylsiloxane) blends

Symmetric polystyrene (PS)–poly(dimethylsiloxane) (PDMS) diblock copolymers were mixed into a 20% dispersion of PDMS in PS. The effect of adding the block copolymer on the blend morphology was examined as a function of the block copolymer molecular weight (M_n,bcp), concentration, and viscosity ratio (η_r). When blended together with the PS and PDMS homopolymers, most of the block copolymer appeared as micelles in the PS matrix. Even when the copolymer was preblended into the PDMS dispersed phase, block copolymer micelles in the PS matrix phase were observed with transmission electron microscopy after mixing. Adding 16 kg/mol PS–PDMS block copolymer dramatically reduced the PDMS particle size, but the morphology, as examined by scanning electron microscopy, was unstable upon thermal annealing. Adding 156 kg/mol block copolymer yielded particle sizes similar to those of blends with 40 or 83 kg/mol block copolymers, but only blends with 83 kg/mol block copolymer were stable after annealing. For a given value of M_n,bcp, a minimum PDMS particle size was observed when η_r ～ 1. When η_r = 2.6, thermally stable, submicrometer particles as small as 0.6 μm were observed after the addition of only 3% PS–PDMS diblock (number‐average molecular weight = 83 kg/mol) to the blend. As little as 1% 83 kg/mol block copolymer was sufficient to stabilize a 20% dispersion of 1.1‐μm PDMS particles in PS. Droplet size reduction was attributed to the prevention of coalescence caused by small amounts of block copolymer at the interface. The conditions under which block copolymer interfacial adsorption and interpenetration were facilitated were explained with Leibler's brush theory. © 2002 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 40: 346–357, 2002; DOI 10.1002/polb.10098     

Direct observation of a diblock copolymer-induced microemulsion at a polymer/polymer interface

We have studied the segregation of a block copolymer of poly(d₈-styrene-b-2-vinylpyridine) (dPS-PVP) at the interface between polystyrene and a random copolymer of poly(styreneran-4-hydroxystyrene) (PS-r-PPHS). Forward recoil spectrometry (FRES) was used to measure the equilibrium excess (z^*) of the dPS-PVP chains at the interface as a function of its volume fraction in the bulk PS phase (?_∞). It was found that there is a sharp increase in z^* at a critical value of ?_∞. This upturn indicates the formation of a microemulsion of PS and the random copolymer PS-r-PPHS due to a vanishing of the interfacial tension caused by the strong adsorption of the block copolymer. Cross-sectional transmission electron microscopy (TEM) of the interface shows that this microemulsion starts to form at the interface by forming a deeply corrugated structure where the “wavelength” of the corrugations is of the order of 50 nm. © 1995 John Wiley & Sons, Inc.     

A lutetium allyl complex that bears a pyridyl-functionalized cyclopentadienyl ligand: dual catalysis on highly syndiospecific and cis-1,4-selective (co)polymerizations of styrene and butadiene

A novel linked‐half‐sandwich lutetium–bis(allyl) complex [(C₅Me₄? C₅H₄N)Lu(η³‐C₃H₅)₂] ( 1 ) attached by a pyridyl‐functionalized cyclopentadienyl ligand was synthesized and fully characterized. Complex 1 in combination with [Ph₃C][B(C₆F₅)₄] exhibited unprecedented dual catalysis with outstanding activities in highly syndiotactic (rrrr>99 %) styrene polymerization and distinguished cis‐1,4‐selective (99 %) butadiene polymerization, respectively. Strikingly, this catalyst system exhibited remarkable activity (396 kg copolymer (mol_Lu h)^?1) for the copolymerization of butadiene and styrene. Irrespective of whether the monomers were fed in concurrent mode or sequential addition of butadiene followed by styrene, diblock copolymers were obtained exclusively, which was confirmed by a kinetics investigation of monomer conversion of copolymerization with time. In the copolymers, the styrene incorporation rate varied from 4.7 to 85.4 mol %, whereas the polybutadiene (PBD) block was highly cis‐1,4‐regulated (95 %) and the polystyrene segment remained purely syndiotactic (rrrr>99 %). Correspondingly, the copolymers exhibited glass transition temperatures (T_g) around ?107 °C and melting points (T_m) around 268 °C; typical values for diblock microstructures. Such copolymers cannot be accessed by any other methods known to date. X‐ray powder diffraction analysis of these diblock copolymers showed that the crystallizable syndiotactic polystyrene (syn‐PS) block was in the toluene δ clathrate form. The AFM micrographs of diblock copolymer showed a remarkable phase‐separation morphology of the cis‐1,4‐PBD block and syn‐PS block. This represents the first example of a lutetium‐based catalyst showing both high activity and selectivity for the (co)polymerization of styrene and butadiene.     

Glass transitions and mixed phases in block SBS

Differential scanning calorimetry (DSC) does not allow for easy determination of the glass‐transition temperature (T_g) of the polystyrene (PS) block in styrene–butadiene–styrene (SBS) block copolymers. Modulated DSC (MDSC), which deconvolutes the standard DSC signal into reversing and nonreversing signals, was used to determine the (T_g) of both the polybutadiene (PB) and PS blocks in SBS. The T_g of the PB block was sharp, at ?92 °C, but that for the PS blocks was extremely broad, from ?60 to 125 °C with a maximum at 68 °C because of blending with PB. PS blocks were found only to exist in a mixed PS–PB phase. This concurred with the results from dynamic mechanical analysis. Annealing did not allow for a segregation of the PS blocks into a pure phase, but allowed for the segregation of the mixed phase into two mixed phases, one that was PB‐rich and the other that was PS‐rich. It is concluded that three phases coexist in SBS: PB, PB‐rich, and PS‐rich phases. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 276–279, 2005     

Dynamic mechanical properties of sulfonated polystyrene/alumina composites

Amino units were grafted onto the surface of small particle size alumina by reaction with 3-aminopropyltriethoxysilane. Atactic polystyrene (PS) was sulfonated (1-14 mol% sulfonation) and mixed with both modified and unmodified alumina at filler loadings varying from 30 to 80 wt %. The resulting composites were characterized by differential scanning calorimetry, Fourier transform infra-red spectroscopy, and dynamic mechanical spectroscopy in the glass transition region at a frequency of 1 Hz. Whereas mixtures of unsulfonated PS with either filler showed essentially no change in T_g with filler content, sulfonated PS saw its T_g increase as a function of filler loading at a rate which was greater following modification of the alumina. At a fixed filler loading of 30 wt%, the composite rubbery plateau modulus was found to increase with copolymer sulfonic acid content, while the loss tangent maximum corresponding to the glass transition broadened and decreased. These observations were interpreted as a manifestation of the decrease in polymer mobility brought upon by the formation of noncovalent crosslinks resulting from the proton transfer from the sulfonic acid units on the polymer to hydroxyl and/or amino units at the surface of the filler. © 1994 John Wiley & Sons, Inc.     

Tailored adhesion at polymer/nonpolymer interfaces

In this investigation, block copolymers of deuterated polystyrene (dPS) and poly (2-vinylpyridine) (PVP) have been used to modify the adhesion at polystyrene/soda lime glass interfaces. The fracture energy, G_s of these interfaces was measured using an asymmetric double cantilever beam specimen. The failure mechanism was investigated using forward recoil spectrometry (FRES) and Rutherford backscattering spectrometry (RBS). The areal density, ∑ of the dPS-PVP block copolymer at the two fracture surfaces, as well as the fraction of the dPS block on the PS side of the fractured sample are measured directly by FRES. The fraction of the PVP block on the glass side of the interface can be found by quaternizing the PVP with methyl iodide and then using RBS to measure the amount of iodine on each fracture surface. Short dPS blocks (N_dPS < 175) do not entangle effectively with the PS homopolymer and only very small increases in G_c can be achieved as the dPS block pulls out of the interface. If the dPS block is long (N_dPS ? 175) and if ∑ is large, crazes can develop in the PS ahead of the crack. The crazed interface fails at low ∑ by breaking the block copolymer close to the styrene/vinylpyridine link. At higher ∑, if the PVP block is relatively short (N_PVP = 95), the crazed interface fails by the PVP block being pulled off the glass. If both the PVP and dPS blocks are long (? 175), the G_c increases rapidly with increases in ∑, but the interface becomes so strong that the glass on the thinner side of the test specimen breaks. The dPS block and the PVP block are found on opposite sides of the fracture surface with most of the PVP on the glass and most of the dPS on the PS side of the interfaces. Finally, if the glass surface is modified by coating it with a self-assembled hydrophobic monolayer produced from chlorodimethyloctadecylsilane (CDMOS), the interface becomes very weak and fails by pull-off of the PVP from the CDMOS-coated glass. Using these results it is possible to tailor the interfacial adhesion to produce a desired G_c within a wide range of possible values. © 1994 John Wiley & Sons, Inc.     

Quantifying phase behavior in partially miscible polystyrene/poly(styrene‐co‐4‐bromostyrene) blends

The phase behavior of thin‐film blends of polystyrene (PS) and the random copolymer poly(styrene‐co‐4‐bromostyrene) (PBS) was studied with atomic force microscopy (AFM) and small‐angle X‐ray scattering (SAXS). Phase behavior was studied as a function of the PBS and PS degree of polymerization (N), degree of miscibility [controlled via the volume fraction of bromine in the copolymer (f)], and annealing conditions. The Flory–Huggins interaction parameter χ was measured directly from SAXS as a function of temperature and scaled with f as χ = f²χ_S–BrS [where χ_S–BrS represents the segmental interaction between PS and the homopolymer poly(4‐bromostyrene)] Simulations based on the Flory–Huggins theory and χ measured from SAXS were used to predict phase diagrams for all the systems studied. The PBS/PS system exhibited upper critical solution temperature behavior. The AFM studies showed that increasing f in PBS led to progressively different morphologies, from flat topography (i.e., one phase) to interconnected structures or islands. In the two‐phase region, the morphology was a strong function of N (due to changes in mobility). A comparison of the estimated PBS volume fractions from the AFM images with the PBS bulk volume fraction in the blend suggested the encapsulation of PBS in PS, supporting the work of previous researchers. Excellent agreement between the phase diagram predictions (based on χ measured by SAXS) and the AFM images was observed. These studies were also consistent with interdiffusion measurements of PBS/PS interfaces (with Rutherford backscattering spectroscopy), which indicated that the interdiffusion coefficient decreased with increasing χ in the one‐phase region and dropped to zero deep inside the two‐phase region. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 40: 255–271, 2002     

Mesomorphic and conducting properties of dendritic‐linear copolymers via ion‐doped additives

We studied the conducting and mesomorphic behavior of a dendritic‐linear copolymer on adding hydrophilic additives and lithium salts. For the preparation of the pristine block copolymer ( A ), a click reaction of a hydrophobic Y‐shaped dendron block and a hydrophilic linear poly(ethylene oxide) coil with M_n = 750 g mol^?1 was performed. For ionic block copolymer samples ( 1–3 ), a hydrophilic compound ( B ) bearing two tri(ethylene oxide) chains was used as the additive. In all ionic samples, the lithium concentration per ethylene oxide was chosen to be 0.05. As characterized by polarized optical microscopy and small angle X‐ray scattering techniques, copolymer A showed a hexagonal columnar mesophase. On addition of lithium‐doped additives, ionic samples 1 and 2 with the additive weight fractions (f_w) of 10 and 20%, columnar and bicontinuous structures coexisted in the liquid crystalline phase. On the other hand, ionic sample 3 with f_w = 30% displayed only a bicontinuous cubic mesophase. Based on the impedance results, with increasing the amount of additives, the conductivity value increased from 3.80 × 10^?6 to 2.34 × 10^?5 S cm^?1 at 35 °C. The conductivity growth could be explained by the interplay of the plasticization effect of the mobile additive and the morphological transformation from 1D to 3D of the ion‐conducting cylindrical cores. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

The synthesis and self‐assembly of ABA amphiphilic block copolymers containing styrene and oligo(ethylene glycol) methyl ether methacrylate in dilute aqueous solutions: Elevated cloud point temperatures for thermoresponsive micelles

A series of ABA amphiphilic triblock copolymers possessing polystyrene (PS) central hydrophobic blocks, one group with “short” PS blocks (DP = 54–86) and one with “long” PS blocks (DP = 183–204) were synthesized by atom transfer radical polymerization. The outer hydrophilic blocks were various lengths of poly(oligoethylene glycol methyl ether) methacrylate, a comb‐like polymer. The critical aggregation concentrations were recorded for certain block copolymer samples and were found to be in the range circa 10⁻⁹ mol L⁻¹ for short PS blocks and circa 10⁻¹² mol L⁻¹ for long PS blocks. Dilute aqueous solutions were analyzed by transmission electron microscopy (TEM) and demonstrated that the short PS block copolymers formed spherical micelles and the long PS block copolymers formed predominantly spherical micelles with smaller proportions of cylindrical and Y‐branched cylindrical micelles. Dynamic light scattering analysis results agreed with the TEM observations demonstrating variations in micelle size with PS and POEGMA chain length: the hydrodynamic diameters (D_H) of the shorter PS block copolymer micelles increased with increasing POEGMA block lengths while maintaining similar PS micellar core diameters (D_C); in contrast the values of D_H and D_C for the longer PS block copolymer micelles decreased. Surface‐pressure isotherms were recorded for two of the samples and these indicated close packing of a short PS block copolymer at the air–water interface. The aggregate solutions were demonstrated to be stable over a 38‐day period with no change in aggregate size or noticeable precipitation. The cloud point temperatures of certain block copolymer aggregate solutions were measured and found to be in the range 76–93 °C; significantly these were ∼11 °C higher in temperature than those of POEGMA homopolymer samples with similar chain lengths. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 7739–7756, 2008     

Microphase separation in block‐random copolymers of styrene, 4‐acetoxystyrene,and 4‐hydroxystyrene

“Block‐random” copolymers—where one or more blocks are themselves random copolymers—offer a flexible modification to the usual block copolymer architecture. For example, in a poly(A)‐poly(A‐ran‐B) diblock consisting of monomer units A and B, the interblock segregation strength can be continuously tuned through the B content of the random block, allowing the design of block copolymers with accessible order‐disorder transitions at arbitrarily high molecular weights. Moreover, the development of controlled radical polymerizations has greatly expanded the palette of accessible monomer units A and B, including units with strongly interacting functional groups. We synthesize a range of copolymers consisting of styrene (S) and acetoxystyrene (AS) units, including copolymers where one block is P(S‐ran‐AS), through nitroxide‐mediated radical polymerization. At sufficiently high molecular weights, near‐symmetric PS‐PAS diblocks show well‐ordered lamellar morphologies, while dilution of the repulsive S‐AS interactions in PS‐P(S‐ran‐AS) diblocks yields a phase‐mixed morphology. Cleavage of a sufficient fraction of the AS units in a phase‐mixed PS‐P(S‐ran‐AS) diblock to hydrogen‐bonding hydroxystyrene (HS) units yields, in turn, a microphase‐separated melt. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47:2106–2113, 2009.     

Determination of block size in poly(ethylene oxide)‐b‐polystyrene block copolymers by matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry

Characterization of block size in poly(ethylene oxide)‐b‐poly(styrene) (PEO‐b‐PS) block copolymers could be achieved by matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry (MALDI‐TOF‐MS) after scission of the macromolecules into their constituent blocks. The performed hydrolytic cleavage was demonstrated to specifically occur on the targeted ester function in the junction group, yielding two homopolymers consisting of the constitutive initial blocks. This approach allows the use of well‐established MALDI protocols for a complete copolymer characterization while circumventing difficulties inherent to amphiphilic macromolecule ionization. Although the labile end‐group in PS homopolymer was modified by the MALDI process, PS block size could be determined from MS data since polymer chains were shown to remain intact during ionization. This methodology has been validated for a PEO‐b‐PS sample series, with two PEO of number average molecular weight (M_n) of 2000 and 5000 g mol^?1 and M_n(PS) ranging from 4000 to 21,000 g mol^?1. Weight average molecular weight (M_w), and thus polydispersity index, could also be reached for each segment and were consistent with values obtained by size exclusion chromatography. This approach is particularly valuable in the case of amphiphilic copolymers for which M_n values as determined by liquid state nuclear magnetic resonance might be affected by micelle formation. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3380–3390, 2009     

Fddd network phase in ABA triblock copolymer melts

Using self‐consistent field theory, we investigate the stability of the orthorhombic Fddd network phase (O⁷⁰) in ABA triblock copolymer melt systems. Consistent with previous findings, we observe that the gross topology of phase behavior is unchanged with varying chain asymmetry. However, the mean field critical point is displaced from the diblock copolymer value of f_A = 0.5 (f_A is the A segment volume fraction) to larger values as the triblock copolymer symmetry is broken with unequal A block lengths. This deviation significantly shifts the order‐order phase boundaries, resulting in an appreciable region of O⁷⁰ stability in the phase diagram of asymmetric ABA triblock copolymers. More importantly, the stability of the O⁷⁰ phase extends to the intermediate segregation regime for select chain asymmetries. Both features are desirable for achieving a synthetic realization of the phase in binary AB block copolymer systems. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 1112–1117     

How did we find the rigid amorphous phase?

The first experimental evidence of the existence of the rigid amorphous phase was reported by Menczel and Wunderlich [1]: when trying to clarify the glass transition characteristics of the first main chain liquid crystalline polymers [poly(ethylene terephthalate-co-p-oxybenzoate) with 60 and 80 mol% ethylene terephthalate units] [2], the absence of the hysteresis peak at the lower temperature glass transition became evident when the sample of this copolymer was heated much faster than it had previously been cooled. Since this glass transition involved the ethylene terephthalate-rich segments of the copolymer, we searched for the source of the absence of the hysteresis peak in PET. There, the gradual disappearance of the hysteresis peak with increasing crystallinity was confirmed [1]. At the same time it was noted that the higher crystallinity samples showed a much smaller ΔC _p than could be expected on the basis of the crystallinity calculated from the heat of fusion (provided that the crystallinity concept works). Later it was confirmed that the hysteresis peak is also missing at the glass transition of nematic glasses of polymers. When checking other semicrystalline polymers, the sum of the amorphous content calculated from the ΔC _p at the glass transition, and the crystallinity calculated from the heat of fusion was far from 100% for a number of semicrystalline polymers. For most of these polymers, the sum of the amorphous content and the crystalline fraction was 0.7, meaning that ca. 30% rigid amorphous fraction was present in these samples after a cooling at 0.5 K min⁻¹ rate. Thus, the presence of the rigid amorphous phase was confirmed in five semicrystalline polymers: PET, Nylon 6, PVF, Nylon 66 and polycaprolactone [1]. Somewhat later poly(butylene terephthalate) and bisphenol-A polycarbonate [3] were added to this list.     

Hyperbranched block copolymer from AB2 macromonomer: Synthesis and its reaction‐induced microphase separation in epoxy thermosets

In this contribution, we reported the synthesis of a hyperbranched block copolymer composed of poly(ε‐caprolactone) (PCL) and polystyrene (PS) subchains. Toward this end, we first synthesized an α‐alkynyl‐ and ω,ω′‐diazido‐terminated PCL‐b‐(PS)₂ macromonomer via the combination of ring‐opening polymerization and atom transfer radical polymerization. By the use of this AB₂ macromonomer, the hyperbranched block copolymer (h‐[PCL‐b‐(PS)₂]) was synthesized via a copper‐catalyzed Huisgen 1,3‐dipolar cycloaddition (i.e., click reaction) polymerization. The hyperbranched block copolymer was characterized by means of ¹H nuclear magnetic resonance spectroscopy and gel permeation chromatography. Both differential scanning calorimetry and atomic force microscopy showed that the hyperbranched block copolymer was microphase‐separated in bulk. While this hyperbranched block copolymer was incorporated into epoxy, the nanostructured thermosets were successfully obtained; the formation of the nanophases in epoxy followed reaction‐induced microphase separation mechanism as evidenced by atomic force microscopy, small angle X‐ray scattering, and dynamic mechanical thermal analysis. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 368–380     

POE incorporation into ionic clusters of ionomer and ion-conduction behaviors

Poly(oxyethylene) (POE) was incorporated into the ionic clusters of ionomers, ethylene and methacrylic acid (7.2% neutralized with KOH) copolymer membrane. The changes of properties were studied from SAXS, DSC, IR and ionic conductivity. The IR study suggested that the coordinated structures in ionic clusters of the membrane were destroyed by POE incorporation, and also SAXS suggested that ionic clusters were swollen by POE incorporation. The ionic conductivity, a carrier being K⁺ in this system, increases from 10^?16 S/cm to 10^?9 S/cm at 30°C by the incorporation of POE (20.5 wt%). On the other hand, a large amount of POE (63 wt%) could be incorporated into ionomer membrane by the esterification of methacrylic acid groups (93%) with POE. When LiClO₄ was added, ionic conduction occurred in the phase-separated POE domain, which had a low glass transition temperature (?55.2°C), showing an ionic conductivity 2.6 × 10^?6 S/cm at 25°C.     

Inverse emulsions in a molten salt/hydroxy-terminated polybutadiene system using block copolymers as emulsifiers

Block copolymers of poly(N-t-butylbenzoyl ethylenimine) and poly(N-propionyl ethylenimine) (B_x/E_y and B_x/E_y/B_x) or poly (N-lauroyl ethylenimine) and poly (N-propionyl ethylenimine) (U_x/E_y) were synthesized by cationic ring-opening polymerization of 2-substituted δ2-oxazolines. Inverse emulsions (salt-in-oil) were made using these block copolymers as emulsifiers, hydroxy-terminated polybutadiene (HTPB) as the nonpolar phase and methyl ammonium ethane sulfonate (MAES) as the polar phase. These inverse emulsions (S/O) were then cured using a triisocyanate to give a dispersion of molten salt (MAES) droplets in polyurethane. Pore sizes of these cured inverse emulsions were measured from scanning electron photomicrographs as a function of stirring time and concentrations of block copolymer and molten salt. The results indicate that pores with diameters in the range of 1.5 X 10^?6 m can be obtained using triblock copolymer B_x/E_y/B_x, and that the surfactant molecules can be spread as a monolayer at the MAES-HTPB interface.     

Phase separation dynamics of a poly(vinyl methyl ether)/polystyrene (PVME/PS) blend studied by ultrafast differential scanning calorimetry

In this work, ultrafast differential scanning calorimetry (UFDSC) is used to study the dynamics of phase separation. Taking poly(vinyl methyl ether)/polystyrene (PVME/PS) blend as the example, we firstly obtained the phase diagram that has lower critical solution temperature (LCST), together with the glass transition temperature (T_g) of the homogeneous blend with different composition. Then, the dynamics of the phase separation of the PVME/PS blend with a mass ratio of 7:3 was studied in the time range from milliseconds to hours, by the virtue of small time and spatial resolution that UFDSC offers. The time dependence of the glass transition temperature (T_g) of PVME‐rich phase, shows a distinct change when the annealing temperature (T_a) changes from below to above 385 K. This corresponds to the transition from the nucleation and growth (NG) mechanism to the spinodal decomposition (SD) mechanism, as was verified by morphological and rheometric investigations. For the SD mechanism, the temperature‐dependent composition evolution in PVME‐rich domain was found to follow the Williams–Landel–Ferry (WLF) laws. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 1357–1364     

Conductivity,structure, and thermal properties of chitosan‐based polymer electrolytes with nanofillers

This paper focus on the effect of nanosize (<50 nm BET) inorganic alumina (Al₂O₃) filler on the structural, conductivity, and thermal properties of chitosan‐based polymer electrolytes. Films of chitosan and its complexes were prepared using solution‐casting technique. Different amounts of Al₂O₃ viz., 3, 4.5, 6, 7.5, 9, 12, and 15 wt% were added to the highest room temperature conducting sample in the chitosan–salt system, i.e. sample containing 60 wt% chitosan–40 wt% NH₄SCN. The conductivity value of the sample is 1.29 × 10^?4 S cm^?1. On addition of 6 wt% Al₂O₃ filler the ionic conductivity increased to 5.86 × 10^?4 S cm^?1. The amide and amino peaks in the spectrum of chitosan at 1636 and 1551 cm^?1, respectively, shift to lower wavenumbers on addition of salt. The glass transition temperature T_g for the highest conducting composite is 190°C. The increase in T_g with increase in more than 6 wt% filler content is attributed to the increase in degree of crystallinity as proven from X‐ray diffraction studies. Copyright © 2009 John Wiley & Sons, Ltd.     

Surfactant addition effects on dispersion and microdomain orientation in SBS triblock copolymer/alumina nanoparticle composites

The aim of this study was to investigate the effects of surfactant addition on the dispersion of 1–3 wt.% alumina nanoparticles on the self-assembled morphology of poly(styrene-b-butadiene-b-styrene) (SBS) linear triblock copolymer. The neat triblock copolymer microphase separated into PS cylinders self-assembled on a hexagonal array in the PB matrix, being the orientation of domains dependent on the annealing conditions. UV–vis and AFM analyses showed an improvement on dispersion of Al₂O₃ nanoparticles into SBS matrix by adding dodecanethiol as organic surfactant, due to its miscibility with PS block. Interactions between surfactant-coated Al₂O₃ nanoparticles with PS block were demonstrated by the variation on the glass transition temperature of this block. AFM analysis showed that the incorporation of surfactant-coated Al₂O₃ nanoparticles in the SBS matrix have great influence on the orientation of microphase separated domains in SBS nanocomposites.