Blends Of Diblock Copolymers Research Articles

Phase Diagram for Blends of Styrene−Butadiene Diblock Copolymer and Styrene−Butadiene Random Copolymer

The phase behaviors of the blends of diblock copolymers and random copolymers were investigated with synchrotron small-angle X-ray scattering, light scattering, differential scanning calorimetry, a...

Properties Controlling the Impact of Styrenic Block Copolymer Based Pressure-Sensitive Adhesives on Paper Recycling

A model was developed for predicting the removal of hot-melt pressure-sensitive adhesives (PSAs) from paper recycling operations via screening using standard adhesive response data. A series of hot-melt PSAs consisting of a styrene−isoprene−styrene/styrene−isoprene linear triblock, diblock copolymer blend, tackifying resin, and naphthenic process oil were blended in combinations to produce a range of properties. The PSAs were formulated with two types of tackifiers, a pentaerythritol ester of rosin and a C5 petroleum hydrocarbon, to provide variation in the formulation composition. The measured removal efficiency versus temperature curves for these PSAs possess a sigmoidal shape, with removal decreasing from 100 to 0% between transitions for the rubbery and polystyrene domains marking significant changes in the mechanical properties. An exponential-based sigmoidal function containing two fitting parameters, inflection temperature and a factor that determines the width of the sigmoid, provided an excellent...

Structure and Dynamics of Blends of Diblock Copolymers

The melt state rheological behavior of a series of blends of a lamellae‐forming nearly symmetrical polystyrene‐polyisoprene (PS‐PI) diblock copolymer with a sphere‐forming highly asymmetrical PS‐PI diblock copolymer is correlated to their structure obtained from small‐angle neutron scattering (SANS). The exponential composition dependence of the relaxation of fluctuations associated with the disordered asymmetrical diblock is similar to that observed in solutions of star polymers. Further, the zero‐shear viscosity of the blends in the disordered state exhibits unusually strong composition dependence. These dynamic properties are closely linked with the SANS‐based structural data that suggest strong compositional fluctuations, even in the disordered state.

Phase behavior of ternary blends of diblock copolymer with homopolymer blends

We theoretically predict phase behavior of ternary blends of two different homopolymers (denoted by A and B) and a diblock copolymer consisting of A- and B monomers. Using a mean-field approach of Landau formalism, the phase diagrams are constructed, and the stability of various microstructures, the biphasic coexistence and the triphasic coexistence comprising ordered phases, are discussed. Our theoretical predictions show that swelling of microphase can be observed only when the molecular weight of added homopolymers is comparable to that of the corresponding block of the copolymer, whereas the addition of sufficiently smaller or larger homopolymers leads to a “dilution” of a ordered phase or various phase coexistence between ordered and disordered phase, respectively.

Morphologies of Binary AB/AC Diblock Copolymer Blends

The self-assembled structures of the mixtures of AB and AC diblock copolymers were investigated using transmission electron microscopy (TEM). For this purpose, two kinds of asymmetric polystyrene-block-polyisoprene (SI30 and SI87) and one symmetric polystyrene-block-poly(2-vinylpyridine) (SVP) were anionically polymerized. Both macro- and microphase separations occur in all binary mixtures examined in this work, yielding various morphologies. The morphologies of the phase-separated macro-domains are found to be the same as those of pure diblock copolymers. However, at the phase boundary where two diblock copolymers with different microphase-separated structures are in contact with each other, the morphological transition is observed due to the preferential location of the common polystyrene (PS) blocks in two copolymers at the interface. From TEM observations and random phase approximation (RPA)-based prediction, it is identified that the macrophase transition takes place prior to the microphase transition,leading to the interface-induced ordering.

Development of Environmentally Benign Pressure-Sensitive Adhesive Systems via Modification of Substrate Properties

Results are presented from a study on a novel approach for reducing the negative impact of pressure-sensitive adhesive (PSA) contaminants on paper recycling. Paper substrates are developed that can be easily removed from the recycling process via screening operations and retain their attached PSAs. A model series of hot-melt PSAs consisting of a styrene−isoprene−styrene/styrene−isoprene (SIS/SI) linear triblock, diblock copolymer blend, a pentaerythritol ester of rosin tackifying resin, and a naphthenic process oil were blended in combinations to produce a range of properties. These PSAs were attached to paper substrates with bulk and surface properties that were manipulated using commercial papermaking chemicals and dosages. A poly(amide epichlorohydrin) wet-strength resin was used to inhibit the fiberization of substrates. Removal efficiencies for PSAs coated on this paper were increased, but poor adhesion between the PSA films and paper substrates during repulping limited the improvement. It was found that the retention of the PSA increased linearly with its mechanical loss tangent indicating that properties of the PSA film could be manipulated to optimize removal efficiencies. It was also found that PSA−paper adhesion could be enhanced without restricting PSA properties by introducing an alkenyl ketene dimer size to the paper. The increased adhesion between PSA films and paper in an aqueous environment was achieved by raising the cellulose−water and lowering the cellulose−PSA interfacial energies. Removal efficiencies for PSAs attached to the sized, wet-strength paper substrates were >90% for all of the experimental hot-melt PSAs. Results of this study indicate that minor modifications made with common papermaking additives to paper used in PSA products can significantly reduce their impact on paper recycling.

The effect of block lengths on micelle structure in blends of styrene–isoprene diblock copolymer and poly(vinyl methyl ether)

The micellar structure of styrene–isoprene diblock copolymer and poly(vinyl methyl ether) blends was investigated by using small-angle X-ray scattering and transmission electron microscopy techniques. In order to determine the effect of styrene block length on the formation of micellar structure, three sets of diblock copolymers, with near-identical isoprene block molecular weights, but with different styrene block lengths were studied. With modeling based on the polydisperse Percus–Yevick hard sphere fluid model, the structural parameters characterizing the micelles were determined as a function of copolymer concentrations, temperature, and copolymer block lengths. The core radius was found to decrease on increasing the length of styrene block. The degree of swelling of the corona by PVME increased steadily with increasing the styrene block length.

Noncentrosymmetric Lamellar Phase in Blends of ABC Triblock and ac Diblock Copolymers

The phase behavior of blends of ABC triblock and ac diblock copolymers is examined using self-consistent mean-field theory. Several equilibrium lamellar structures are observed, depending on the volume fraction of the diblocks, φ2, the monomer interactions, and the degrees of polymerization of the copolymers. For segregations just above the order−disorder transition the triblocks and diblocks mix together to form centrosymmetric lamellae. As the segregation is increased, the triblocks and diblocks spatially separate either by macrophase-separating or by forming a noncentrosymmetric (NCS) phase of alternating layers of triblock and diblock (...ABCcaABCca...). The NCS phase is stable over a narrow region near φ2 = 0.4. This region is widest near the critical point on the phase coexistence curve and narrows to terminate at a triple point at higher segregation. Above the triple point there is two-phase coexistence between almost pure triblock and diblock phases. The theoretical phase diagram is consistent with experiments.

A Phase Diagram for the Binary Blends of Nearly Symmetric Diblock Copolymers. 2. Parameter Space of Temperature and Blend Composition

A phase diagram in the parameter space of temperature and blend composition that contains order−disorder transition (ODT) and thermoreversible macrophase separation between constituent copolymers was constructed for binary blends of polystyrene-block-polyisoprene (PS−PI) copolymers. The constituent copolymers, designated as H102 and FS-1, have nearly symmetric copolymer compositions and rather different molecular weights; i.e., number-average molecular weight (Mn) and volume fraction of PS-block (fPS) are 1.0 × 105 and 0.47 for H102 while 2.1 × 104 and 0.40 for FS-1. The ODT was observed on the neat FS-1 and two blend specimens whose weight fractions of H102, ΦH102, are 0.1 and 0.2. Counterintuitively, the ODT temperature (TODT) decreased with increasing the average molecular weight of the specimen, namely, TODT for FS-1 neat > TODT for the blend of ΦH102 = 0.1 > TODT for the blend of ΦH102 = 0.2. Then TODT abruptly increased between the blends of ΦH102 = 0.2 and 0.3 and became inaccessibly high temperature (i.e., > 200 °C). The macrophase separation between H102 and FS-1 was observed on the blend of ΦH102 = 0.2. This macrophase separation was thermoreversible but accompanied by a hysteresis between cooling and heating processes. Although both H102 and FS-1 neat copolymers showed lamellar morphology, PS cylindrical morphology was observed on certain blend specimens. The origin of PS cylindrical morphology may be attributed to the slight asymmetry in the fPS of FS-1.

A Phase Diagram for the Binary Blends of Nearly Symmetric Diblock Copolymers. 1. Parameter Space of Molecular Weight Ratio and Blend Composition

A phase diagram as a function of molecular weight ratio and blend composition was constructed for the binary blends of nearly symmetric polystyrene-block-polyisoprene (PS−PI) copolymers. In this study we prepared four series of binary blends, and every blend consists of a copolymer, hereafter designated as α, whose number-average molecular weight (Mn) and volume fraction of PS-block (fPS) are 1.0 × 105 and 0.47, respectively. Four PS−PI copolymers (hereafter designated β), each of which is blended with α, have their Mn and fPS in the range 1.2 × 104−2.1 × 104 and 0.40−0.49, respectively, and therefore the molecular weight ratio of α to β, hereafter designated as r, ranges between 4.8 and 8.3. All the blends showed partial miscibility of the constituent copolymers; that is, at a certain blend composition the macrophase separation between α and β occurred. However, the range of blend compositions where the constituent copolymers phase-separate became small as r decreased. As for the two blend series where r...

Micelle Formation in Mixtures of Styrene−Isoprene Diblock Copolymer and Poly(vinyl methyl ether)

The characteristics of micelle formed in blends of styrene-isoprene diblock copolymer (SI) and poly(vinyl methyl ether) (PVME) were investigated by using small-angle X-ray scattering (SAXS), transmission electron microscopy (TEM), and light scattering techniques. The results of SAXS and TEM experiments indicate that the blends form spherical micelles with isoprene-rich cores and styrene-corona mixed with PVME in a matrix of PVME. As temperature increased, the blends underwent macrophase separation into a PVME-rich phase and a SI-rich phase which was also microphase-separated to ordered microdomains. Upon further heating, the ordered structure of the SI-rich region transforms to a disordered phase in a manner resembling the order-disorder transition in pure block copolymer melts.

Polymer‐Based Photonic Crystals

In this report, we highlight the development of polymers as 1D photonic crystals and subsequently place special emphasis on the activities in self-assembled block copolymers as a promising platform material for new photonic crystals. We review recent progress, including the use of plasticizer and homopolymer blends of diblock copolymers to increase periodicity and the role of self-assembly in producing 2D and 3D photonic crystals. The employment of inorganic nanoparticles to increase the dielectric contrast and the application of a biasing field during self-assembly to control the long-range domain order and orientation are examined, as well as in-situ tunable materials via a mechanochromic materials system. Finally, the inherent optical anisotropy of extruded polymer films and side-chain liquid-crystalline polymers is shown to provide greater degrees of freedom for further novel optical designs.

Synthesis, characterization and protein adsorption behaviors of PLGA/PEG di-block co-polymer blend films

A series of poly( d,l-lactic-co-glycolic acid) (PLGA)/poly(ethyleneglycol) (PEG) di-block copolymers were synthesized by ring-opening polymerization of d,l-lactide and glycolide with different molecular weights of monomethoxy polyethyleneglycol (mPEG) 750, 2000 and 5000 as an initiator. The bulk properties of these co-polymers were characterized by using 1H NMR spectroscopy, gel permeation chromatography, differential scanning calorimetry (DSC). Electron spectroscopy for chemical analysis (ESCA) results, in which the blend films with the di-block copolymers showed increasing surface oxygen atomic percentage with increasing PEG chain length, indicate that PEG chain segment in the di-block copolymers is surface oriented and enriched onto the surface of the blend films. The extent of protein adsorption onto the surface of these blend films was studied, using iodine radio-labeled human serum albumin, gamma globulin and human growth hormone. The protein adsorption amount was reduced for the blend films prepared with PLGA/PEG 750 and 2000 di-block copolymers, but increased to a great extent for PLGA/PEG 5000 di-block copolymer. This is due to the increased water uptake capacity of the blend film, which absorbed more protein molecules into a swollen polymer matrix in addition to surface adsorption.

Blends of block copolymers

The formation of superlattices in blends of lamellar ABC triblock and AC diblock copolymers is investigated for two systems with A being polystyrene (S), B being polybutadiene (B) and C being poly(methyl methacrylate) (M) or poly(tert. butyl methacrylate) (T). While in the SBM/SM blends either macrophase separation between the two block copolymers or a cylindrical superlattice was found, in the blend of SBT/ST a non-centrosymmetric periodic lamellar superlattice was obtained.

Microphase and Macrophase Transitions in Binary Blends of Diblock Copolymers

The macro- and microphase transitions in binary blends of poly(styrene-b-isoprene) (SI) and poly(styrene-b-ethylenepropylene) (SEP) lamellar diblock copolymers were investigated by optical and elec...

Phase behavior of binary blends of symmetric polystyrene-polybutadiene diblock copolymers studied using SANS

Binary blends of compositionally symmetric diblock copolymers are investigated using small-angle neutron scattering. The study focuses on the miscibility of blends of polystyrene-polybutadiene diblock copolymers as a function of chain length ratio and blend composition, and the results are related to the theoretical phase diagram put forward by M.W. Matsen (J. Chem. Phys. 103, 3268 (1995)). Three different low molar mass copolymers were blended with a high molar mass copolymer. We find very good coincidence with the theoretical phase diagram obtained. Only for blends having a chain length ratio of 0.06, theory predicts that a larger amount of short copolymers can be dissolved in the matrix of long copolymers, and vice versa. With the latter blends and volume fractions of short chains between 0.11 and 0.70, the second-order Bragg-peaks do not vanish, which indicates that the lamellae are asymmetric.

Self-assembly of block copolymers

In the past year, several theories of anisotropic fluctuations in ordered copolymer phases have been merged with the detailed studies of these complex phases which have been ongoing since the mid 1990s. Subtle issues have been clarified which related to the stability of the ordered phases and the kinetic pathways between these phases, as well as those between ordered and disordered phases. An extension of these activities to studies on blends of diblock copolymers and diblock/homopolymers, both theoretical and experimental, is now beginning to develop.

Ordering in Blends of Diblock Copolymers

The morphology of binary blends of poly(styrene)−poly(2-vinylpyridine) (PS−PVP) diblock copolymers of the type (A−B)α + (A−B)β was examined in a thin-film geometry using neutron reflection (NR), transmission electron microscopy (TEM), and self-consistent field (SCF) calculations. Blends of symmetric diblock copolymers (fA,α ≈ fA,β ≈ 0.5) revealed a localization of the lower molecular weight diblock copolymer and stretching of the higher molecular weight diblock copolymer near the AB interface that is qualitatively consistent with the data of a prior study by Mayes and co-workers. Blends of asymmetric diblock copolymers of the type fA,α < 0.5 and fA,β > 0.5 having similar molecular weights (Nα ≈ Nβ) and with ∼50% overall composition of a chemically similar block in the blend, 〈fA〉 ≈ 0.5, revealed molecular-level mixing of the two components and the formation of a single-phase morphology. A lamellar morphology was formed even when the individual components exhibit a nonlamellar morphology in the pure melt state. In general, the morphological characteristics are well anticipated by SCF calculations. After accounting for fluctuations at the interface, spatial distributions of the individual components in the blend obtained by SCF calculations were in close agreement with the NR data. For diblock copolymers near the order−disorder transition, a χ value higher than the bulk was necessary to fit the experimental data, suggesting an enhancement of ordering in the thin films near the transition due to the presence of the surfaces.

Thermally induced morphological transition from lamella to gyroid in a binary blend of diblock copolymers

We report an experimental result of the thermally induced morphological transition from lamellar to gyroid phase in a binary blend of polystyrene-block-polyisoprene (SI) diblock copolymers. Two SI copolymers employed in this study have almost the same molecular weights but different volume fractions of polystyrene (PS) block (φPS=0.26 and 0.65). The blend was prepared by these two SI diblock copolymers and the overall volume fraction of PS block in the blend, φPS¯, was 0.58. Time-resolved small-angle x-ray scattering (SAXS) experiments were conducted to reveal morphological structures as a function of temperature from 120 to 205 °C during the heating with a rate of 2 °C/min. It was observed from SAXS results that the lamellar phase (L) was found below 164 °C, the gyroid phase (G) above 188 °C, and the coexistence of L and G phases between these temperatures. The gyroid phase was confirmed by transmission electron micrograph. The transition from L to G phase is different from a thermally induced transition of kinetically locked morphology formed by the vitrification of the PS matrix, because it was also found by a separate SAXS experiment for the specimen annealed for long times in which the lamellar phase was stable up to 140 °C, which is well above the glass transition temperature of the PS block. A temperature sweep of SAXS experiment with a smaller heating rate was a useful method to roughly estimate the transition temperature. Moreover, it was found from this experiment that the position of the first-order peak does not change remarkably upon the transition. Although the thermoreversibility of the transition between L and G phases has not yet been confirmed, it does not necessarily mean that the lamellar morphology is not stable at lower temperatures.

Morphological Control in Binary Blends of Diblock Copolymers

Morphological Control in Binary Blends of Diblock Copolymers