Viscoelastic behavior,order-disorder transition,and phase equilibria in mixtures of a block copolymer and an endblock-associating resin

The viscoelastic behavior, order-disorder transition, and phase equilibria in mixtures of a block copolymer and an endblock-associating resin were investigated. The block copolymer was a polystyrene-block-polyisoprene-block-polystyrene (KRATON® D-1107, Shell Development Co.) copolymer. The endblock-associating resins investigated were two different grades of a commercially available random copolymer of poly(α-methyl styrene) and polystyrene, one with a weight-average molecular weight \[\bar M_{\rm w}\] of 710 (KRISTALEX® 3085, Hercules Inc.) and the other with \[\bar M_{\rm w}\] = 4100 (KRISTALEX® 5140, Hercules Inc.). Mixtures of various proportions of the block copolymer and the endblock-associating resin were prepared in toluene solvent. With the mixtures, measurements of dynamic viscoelastic properties were made, namely, dynamic storage modulus G″ and dynamic loss modulus G″ as a function of temperature from temperature scans of the samples using a Rheometrics Mechanical Spectrometer. The following observations were made. (1) The plateau modulus of the block copolymer increased with increasing amount of KRISTALEX 3085 or KRISTALEX 5140, indicating that the low-molecular-weight resin was associated with the polystyrene microdomains of the block copolymer. (2) When KRISTALEX 3085 (up to 30 wt %) was added to the block copolymer, the glass transition temperature (T_g) of the polyisoprene midblock of the SIS block copolymer was shifted toward higher temperatures, indicating that part of the KRISTALEX 3085 added had associated with the rubbery midblock of the block copolymer. Also investigated was the order-disorder transition behavior of the mixtures, using a rheological technique (log G′ versus log G″ plots) recently introduced by Han and Kim. It has been found that the order-disorder transition temperature T_r of mixtures of the SIS block copolymer and KRISTALEX 3085 decreased steadily with increasing amount of KRISTALEX 3085, whereas the addition of KRISTALEX 5140 increased the T_r of the block copolymer. It was found by light scattering and hot-stage microscopy that macrophase separation occurred in the KRATON 1107/KRISTALEX 5140 mixtures while microdomains of polystyrene were present in the block copolymer.     

Phase behavior in mixtures of a homopolymer and a block copolymer 1. FTIR and DSC studies

Miscibility in blends of three styrene-butadiene-styrene and one styrene-isoprene-styrene triblock copolymers containing 28%, 30%, 48%, and 14% by weight of polystyrene, respectively, with poly(vinyl methyl ether) (PVME) were investigated by FTIR spectroscopy and differential scanning calorimetry (DSC). It was found from the optical clarity and the glass transition temperature behavior that the blends show miscibility for each kind of triblock copolymers below a certain concentration of PVME. The concentration range to show miscibility becomes wider as the polystyrene content and molecular weight of PS segment in the triblock copolymers increase. From the FTIR results, the relative peak intensity of the 1100 cm^-1 region due to COCH₃ band of PVME and peak position of 698 cm^-1 region due to phenyl ring are sensitive to the miscibility of SBS(SIS)/PVME blends. The results show that the miscibility in SBS(SIS)/PVME blends is greatly affected by the composition of the copolymers and the polystyrene content in the triblock copolymers. Molecular weights of polystyrene segments have also affected the miscibility of the blends. ©1995 John Wiley & Sons, Inc.     

High-temperature morphological transition in a styrene-butadiene-styrene block copolymer

Electron microscopy reveals a high-temperature morphological transition in a styrene-butadiene-styrene block copolymer of 7000 polystyrene block molecular weight and 43,000 polybutadiene block molecular weight (7S-43B-7S). Samples quenched in liquid nitrogen from temperatures above 150°C show no structure, whereas those quenched from temperatures below 140°C clearly show a multiphase structure. We previously reported that the 7S-43B-7S polymer exhibits a relatively sharp melt rheological transition in the temperature region between 140 and 150°C from highly viscoelastic and nonlinear viscous behavior to linear viscous behavior with insignificant elasticity. The dynamic viscoelastic properties are measured at different strain amplitudes in this study, and the results show that the melt rheological transition behavior is not influenced by the strain amplitude. This study clearly shows that the melt rheological transition in the 7S-43B-7S results from a morphological transition from a multiphase structure below about 140°C to a single-phase structure above about 150°C.     

Phase behavior in mixtures of a homopolymer and a block copolymer. 4. SALS and SAXS studies

Phase behavior of blends of poly(vinyl methyl ether) (PVME) with four styrene-butadiene-styrene (SBS) triblock copolymers, being of various molecular weights, architecture, and compositions, was investigated by small-angle light scattering. Small-angle X-ray scattering investigation was accomplished for one blend. Low critical solution temperature (LCST) and a unique phase behavior, resembling upper critical solution temperature (UCST), were observed. It was found that the architecture of the copolymer greatly influenced the phase behavior of the blends. Random phase approximation theory was used to calculate the spinodal phase transition curves of the ABA/C and BAB/C systems; LCST and resembling UCST phase behavior were observed as the parameters of the system changed. Qualitatively, the experimental and the theoretical results are consistent with each other. © 1996 John Wiley & Sons, Inc.     

Effects of confinement on the order-disorder transition of diblock copolymer melts

The effects of confinement on the order-disorder transition of diblock copolymer melts are studied theoretically. Confinements are realized by restricting diblock copolymers in finite spaces with different geometries (slabs, cylinders, and spheres). Within the random phase approximation, the correlation functions are calculated using the eigenvalues and eigenfunctions of the Laplacian operator inverted Delta(2) in the appropriate geometries. This leads to a size-dependent scattering function, and the minimum of the inverse scattering function determines the spinodal point of the homogeneous phase. For diblock copolymers confined in a slab or in a cylindrical nanopore, the spinodal point of the homogeneous phase (chiN)(s) is found to be independent of the confinement. On the other hand, for diblock copolymers confined in a spherical nanopore, (chiN)(s) depends on the confinement and it oscillates as a function of the radius of the sphere. Further understanding of the finite-size effects is provided by examining the fluctuation modes using the Landau-Brazovskii model.     

A reversible tube-to-rod transition in a block copolymer micelle

A remarkable morphology transition occurs with a change in temperature for a diblock copolymer [poly(ferrocenyldimethylsilane-b-dimethylsiloxane) (PFS40-b-PDMS480, PDI = 1.01)] in n-decane solution. This polymer, which forms nanotubes at 25 degrees C, rearranges to form short dense rods when the solution is heated to 50 degrees C. When the solution is cooled to 25 degrees C, the system evolves back to nanotubes. These experiments demonstrate that both structures are dynamic and represent equilibrium states of the material. Contrast matching static light-scattering measurements on the short dense rods show that the insoluble PFS core is rigid and has a length distribution similar to that seen in electron microscopy images.     

Ordering transition of block copolymer films

It is well-known that a bulk, symmetric, A-b-B diblock copolymer forms a lamellar morphology, with period L, below an order-disorder transition (T(ODT)) temperature, for chiN < 10.5; chi is the Flory-Huggins interaction parameter and N is the degree of polymerization of the copolymer. The ordering temperatures of poly(styrene-b-methyl methacrylate) (PS-b-PMMA) thin film diblock copolymers of thickness h 相似文献   

Substrate interaction effects on order to disorder transition behavior in block copolymer films

We present an overview of the recent progress on the phase transition in the block copolymer (BCP) films in terms of the interfacial interactions effects of the substrates and the χ (Flory-Huggins segmental interaction parameter) effects between the two blocks. For the BCP films thinner than a critical thickness (L_c) above which the transition is independent of film thickness, the order-to-disorder transition (ODT) increased or decreased with decreasing film thickness depending on the interfacial interaction types. The rapid and slow changes in the ODT were attributed to the relative magnitude of enthalpic contribution to χ between two blocks. Interestingly, a periodic amplification in the block composition for the BCP films suppressed the compositional fluctuation in the film geometry, resulting in the ODT shifts from the bulk ODTs above L_c. This effect of the BCP films was more illustrated by the ODT shift effects depending on the strength of the preferential interactions on the substrates. © 2013 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2013     

Transient solidlike behavior near the cylinder/disorder transition in block copolymer solutions

A nearly symmetric polystyrene-block-polyisoprene diblock copolymer dissolved at a concentration of 40% in styrene-selective solvents exhibited a cylinder-to-disorder transition upon heating. The solvents used were diethyl phthalate (DEP) and 75:25 and 50:50 mixtures of DEP with di-n-butyl phthalate (DBP). In DEP, the most styrene-selective of the three solvents, rheological measurements indicated a distinct plateau in the temperature-dependent elastic modulus across the 8 degrees C interval above the order-disorder transition temperature, T(ODT) = 116 degrees C. Previous small-angle neutron scattering measurements in this regime indicated the equilibrium phase to be a liquidlike solution of approximately spherical micelles. An isothermal frequency sweep in this regime indicated a very long relaxation time. Annealing eventually led to the recovery of liquidlike rheological response, over a time scale of hours. Qualitatively similar phenomena were also observed in 75:25 DEP/DBP and 50:50 DEP/DBP solutions, except the fact that the temperature window of the transient response is narrow and the time scale for the recovery diminishes significantly. Neither small-angle X-ray scattering nor static birefringence gave any clear signature of the transient structure. The structure that leads to the transient rheological response is attributed to micellar congestion due to the slow relaxation of anisotropic micelles into an equilibrium distribution of micelles. Possible origins of the remarkable solvent selectivity dependence are also discussed.     

Microphase separation transition in block copolymer melts

The microphase separation transition (MST) in block copolymer melts has been studied using synchrotron SAXS. The results indicate that the MST occurs in the range of molecular weights and Flory-Huggins interaction parameters x predicted by the theory of Leibler (Ref. 5). Studies of the MST as a function of molecular weight for constant composition can be used to determine the temperature dependence of x. The observed change of macrolattice constants with temperature is somewhat different from theoretically predicted values.     

Self-assembly via a complex phase transition in mixtures of polystyrene-block -polybutadiene block copolymer and poly(methyl vinyl ether)

The self-assembly of a binary mixture of polystyreneblock-polybutadiene (SB) and poly(methyl vinyl ether) (PVME) was studied by transmission electron microscopy and time-resolved light scattering. The self-assembly studied involved first microphase separation, in which a microdomain structure composed of polybutadiene block chains (PB) was formed in a matrix composed of polystyrene block chains (PS) and PVME homopolymers, and subsequently macrophase separation of the PVME from the microdomain phase of SB. The microphase separation was induced in a film preparation process using a solution cast method at room temperature. The macrophase separation was induced by rapidly heating the film specimens to above a critical temperature where PVME and PS undergo spinodal decomposition (SD). This complex phase transition, involving microphase separation followed by macrophase separation, was found to generate a superlattice structure (or a modulated structure) with two characteristic spacings: A_macro associated with the SD and A_micro associated with the microphase separation, both being generally time-dependent. The growth of the “macrodomains” was found to be pinned at A_macro ˜ 840 nm due to the elastic effect of the microdomain structure. The microdomain structure with A_micro ˜ 57 nm was found to undergo a morphological transition (a transition between two ordered phases of block copolymers) as a consequence of the local composition change of the two polymers induced by the SD.     

Superlattice formation in binary mixtures of block copolymer micelles

Two distinct diblock copolymers, poly(styrene-b-isoprene) (SI) and poly(styrene-b-dimethylsiloxane) (SD), were codissolved at various concentrations in the polystyrene selective solvent diethyl phthalate. Two SI diblocks, with block molar masses of 12,000-33,000 and 30,000-33,000, and two SD diblocks, with block molar masses of 19,000-6000 and 16,000-9000, were employed. The size ratio of the smaller SD micelles (S) to the larger SI micelles (L) varied from approximately 0.5 to 0.6, based on hydrodynamic radii determined by dynamic light scattering on dilute solutions containing only one polymer component. Due to incompatibility between the polyisoprene and polydimethylsiloxane blocks, a binary mixture of distinct SI and SD micelles was formed in each mixed solution, as confirmed by cryogenic transmission electron microscopy. When the total concentration of polymer was increased to 20-30%, the micelles adopted a superlattice structure. Small angle X-ray scattering revealed the lattice to be the full LS13 superlattice (space group Fm3c) in all cases, with unit cell dimensions in excess of 145 nm. A coexistent face-centered cubic phase composed of SD micelles was also observed when the number ratio of S to L micelles was large.     

Viscoelastic behavior of linear polyethylene and of paraffin mixtures

Summary The complex shear modulus of a linear polyethylene (Marlex 50), of which samples were either crystallized from the melt at various temperatures or precipitated from a dilute xylene solution, has been measured as a function of temperature at fixed frequencies between 10⁵ and 10^–1 c/s. The three relaxation regions, , can be distinguished, and activation energies are determined from the relaxation map. The-process shows a frequency-temperature characteristic which has been divided into three parts _I, _II, _III. Further experimental evidence for the kink model, proposed in an earlier paper (reference 4) is taken from the investigation of suitable paraffin mixtures. Measurements on six n-alkane systems, each consisting of an even n-paraffin mixed with a few percent of a paraffin with a chain longer by two C-atoms, are reported.

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Zusammenfassung Es wurde die TemperaturabhÄngigkeit des komplexen Schubmoduls eines linearen PolyÄthylens (Marlex 50) bei festen Frequenzen zwischen 10^–1 und 10⁵ Hz untersucht, wozu die Proben entweder aus der Schmelze bei verschiedenen Temperaturen kristallisiert oder aus verdünnter Xylollösung bei 80 C gefÄllt, in Methanol ausgewaschen und gepre\t worden waren. Drei Dispersionsgebiete, , können unterschieden werden. Die/max-1/T- Charakteristik des -Relaxations-prozesses wird in drei Bereiche _I, _II, _III unterteilt. Aktivierungsenergien werden aus geradlinigen Kurvenstücken dieser Charakteristiken bestimmt.Eine erneute experimentelle Stütze für das in einer früheren Arbeit (4) vorgeschlagene Kinkenmodell stellen Messungen an 6 weiteren n-Paraffin-Mischungssystemen dar, wobei die KettenlÄngen der Mischungspartner sich jeweils um zwei CH₂-Gruppen unterscheiden.

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Parts of this paper were read at the 4th International Congress on Rheology, Providence R. I., 1963.     

Solvent-induced morphological transition in core-cross-linked block copolymer micelles

Microwave-assisted polymerization has been utilized to synthesize amphiphilic poly(2-ethyl-2-oxazoline-block-2-"soy alkyl"-2-oxazoline) diblock copolymers (PEtOx-PSoyOx). The amphiphilic block copolymers have been used to prepare aqueous spherical micelles consisting of a PEtOx corona and a PSoyOx core, which have been further cross-linked by UV irradiation. The morphology of these cross-linked micelles has been shown to reversibly change from spheres to short rods referred to as rice grains whenever the micelles were transferred from water into acetone, a nonselective solvent for the constituent blocks. This morphological transition has been attributed to the swelling of the slightly cross-linked PSoyOx core.     

PEO-PET嵌段共聚物的合成及其热行为研究

合成了聚氧化乙烯－聚对苯二甲酸乙二醇酯（PEO－PET）多嵌段共聚物，以红外光谱（RIR）、核磁共振谱图（NMR）对产物进行了结构表征，结果表明产物的组成与理论基本一致；利用差示扫描量效法研究了PEO－PET共聚物的热行为，发现共聚物中软段PEO与硬段PET的结晶性竞相互作用的影响。     

Managing polymer surface structure using surface active block copolymers in block copolymer mixtures

Surface coatings were prepared from semifluorinated monodendron surface‐active block copolymers (SABC) and a thermoplastic elastomer (TPE) [poly(styrene‐b‐ethylene butylene‐b‐styrene)] by either spin‐casting a bilayer structure or by blending. The surface of these coatings was characterized by contact angle measurements, scanning force microscopy (SFM) and near‐edge X‐ray absorption fine structure (NEXAFS) methods. Both bilayers and blends resulted in very low energy surfaces under the right processing conditions and the liquid crystallinity of the semifluorinated monodendrons gave rise to temporally stable, non‐reconstructing surfaces in water. However for small thicknesses of the SABC top layer or for low SABC content blends, SFM shows islands of the fluorinated block of the SABC and incomplete surface coverage of the TPE, an observation confirmed by NEXAFS analysis. Very high water contact angles were produced by even modest amounts of SABC in either case but to achieve low contact angle hysteresis, it was necessary to produce uniform surface coverage by the SABC. Such uniform coverage can be accomplished by spin casting a top layer of SABC as thin as 60 nm in the bilayer case but at least 10 wt% SABC in TPE combined with drop casting of a hot solutions is needed for the blends to achieve equivalent surface structure and properties. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 411–420, 2004     

Structure, rheology and shear alignment of Pluronic block copolymer mixtures

The structure and flow behaviour of binary mixtures of Pluronic block copolymers P85 and P123 is investigated by small-angle scattering, rheometry and mobility tests. Micelle dimensions are probed by dynamic light scattering. The micelle hydrodynamic radius for the 50/50 mixture is larger than that for either P85 or P123 alone, due to the formation of mixed micelles with a higher association number. The phase diagram for 50/50 mixtures contains regions of cubic and hexagonal phases similar to those for the parent homopolymers, however the region of stability of the cubic phase is enhanced at low temperature and concentrations above 40 wt%. This is ascribed to favourable packing of the mixed micelles containing core blocks with two different chain lengths, but similar corona chain lengths. The shear flow alignment of face-centred cubic and hexagonal phases is probed by in situ small-angle X-ray or neutron scattering with simultaneous rheology. The hexagonal phase can be aligned using steady shear in a Couette geometry, however the high modulus cubic phase cannot be aligned well in this way. This requires the application of oscillatory shear or compression.     

Dilatometric behavior and glass transition in a styrene‐acrylonitrile copolymer

Equilibrium and glass transition behavior of a styrene‐acrylonitrile copolymer (SAN) under different thermobaric histories were studied by means of a PVT dilatometer. Equilibrium behavior, as determined by isothermal and isobaric measurements, could be satisfactorily described using the Simha‐Somcynsky and Tait equations of state. Glass transition behavior depended upon the applied transformation path from the liquid‐equilibrium state to the glassy state. From isobaric cooling ramps performed at constant rate and at several pressures, it was possible to determine the glass transition temperature and its dependence upon pressure; whereas from isothermal compressions at various temperatures, it was possible to determine a glass transition pressure and its temperature dependence. Both the dependences were linear, and a correlation was observed between the slopes of the fitting lines. A possible interpretation of this correlation is provided in terms of free volume determined at the glass transition point by applying the Simha‐Somcynsky theory. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1904–1913, 2005     

Rod-sphere transition in polybutadiene-poly(L-lysine) block copolymer assemblies

This paper describes the synthesis and characterization of poly(butadiene)m-poly(L-lysine)n (m-n = 107-200, 107-100, and 60-50) block copolymers. The polymers are prepared in a two-step process whereby amine-terminated polybutadiene is used to initiate the ring-opening polymerization of the epsilon-benzyloxycarbonyl L-lysine N-carboxyanhydride. After deprotection, the self-assembly of the block copolymers in aqueous media were studied using dynamic light scattering, transmission electron microscopy, and circular dichroism spectroscopy. These block copolymers were found to form either spherical micelles or rod-like micelles at high pH depending on the composition of the block copolymer. As the pH is decreased, the micelles swell due to charge-charge repulsions between corona chains and from the helix-coil transition of the polypeptide block. The two systems that form rod-like micelles at high pH also exhibit a pH-induced rod-sphere transition at low pH. This transition was verified from Kratky analysis of the static light scattering data and via CONTIN analysis of the dynamic light scattering data, which shows a bimodal distribution in particle sizes.