Polybutadiene Diblock Copolymers Research Articles

Distortion of a Unit Cell versus Phase Transition to Nonbulk Morphology in Frustrated Films of Cylinder-Forming Polystyrene-b-polybutadiene Diblock Copolymers

Dimensions of cylindrical domains and microphase separation behavior in thin films of polystyrene-b-polybutadiene diblock copolymer (SB) are analyzed under fine variation of the surface fields, polymer–polymer interactions, film thickness, and the symmetry of the wetting conditions. In thermally and in solvent annealed films the dimensions of the closest to the substrate cylinders are smaller than both in thicker films and in bulk due to the confinement effect. The related excess of the stretching energy favors a transition to nonbulk perforated lamella morphology in a narrow window of the film thickness, solvent concentration, and annealing temperature. The discussion of the apparent stability/instability of thin film morphologies includes the analysis of molecular architecture, interfacial tensions, and possible influence of dynamic effects.

Lamellar Diblock Copolymer Thin Films Investigated by Tapping Mode Atomic Force Microscopy: Molar-Mass Dependence of Surface Ordering

Using tapping mode atomic force microscopy, we studied the influence of molar mass (13.9−183 kg/mol) on the lamellar orientation at the surface of thin films of symmetric polystyrene−polybutadiene diblock copolymers prepared via spin-coating and by slow solvent-casting. The ratio between film thickness and lamellar thickness was varied between 0.5 and 10. Whereas for film thicknesses between 1 and 10 times the lamellar thickness, a lamellar orientation parallel to the film surface is preferred for low molar masses (below ∼55 kg/mol), high molar mass samples (above ∼90 kg/mol) rather form lamellae oriented perpendicular to the surface. For film thicknesses equal to the lamellar thickness, the films do not exhibit any texture, whereas for film thicknesses equal to half the lamellar thickness, a weak surface structure could be observed. This is consistent with symmetric wetting, i.e., the same block adsorbs at both film interfaces, but their selectivity is only weak. Thus, entropic contributions like chain stretching along a wall and the enrichment of free chain ends at the interface become important, and both parallel and perpendicular orientations of lamellae in thin films can occur.

Apparent Slip of Newtonian Fluids Past Adsorbed Polymer Layers

We show unexpected drag reduction as solvent flows past polymer-coated surfaces in solution. Adsorbed polymer layers of two types, poly(vinyl alcohol) (PVA) homopolymers in deionized water and poly(vinylpyridine)−polybutadiene diblock copolymers (PVP−PB) in tetradecane, were placed at variable spacings larger than twice the layer thickness within a modified surface forces apparatus, and the hydrodynamic forces owing to flow of solvent past these layers were measured as a function of surface spacing, pumping frequency, and pumping velocity (product of frequency and amplitude). When the flow rate was below a critical level, which depended on the system, the findings agreed with a simple hydrodynamic picture in which the solvent appeared to flow past surfaces of defined spacing, the solid−solid spacing less twice the “hydrodyamic radius” (RH). The value of RH was not always constant, however. In the PVA system it tripled as frequency was raised from 1 to 50 Hz though it was frequency-independent in the PVP−P...

Block copolymer molecular weight determination via gel permeation chromatography: Choosing a combining rule

AbstractWe present a method for accurately determining the true molecular weights of narrow‐distribution block copolymers, using only a basic gel permeation chromatograph (GPC) equipped with a refractive index detector and calibrated with polystyrene standards. Our approach is based on the well‐known observation that GPC calibration curves for different homopolymers in good solvents are essentially parallel, allowing the curves for different polymers to be described by simple hydrodynamic equivalence ratios rB versus polystyrene. We present values of rB, in both toluene and tetrahydrofuran, for various polydiene and hydrogenated polydiene homopolymers commonly incorporated into commercial styrenic block copolymers. These values of rB must be combined to yield the hydrodynamic equivalence ratio of the block copolymer, from which the block copolymer's true molecular weight can be determined. Three combining rules proposed in the literature are tested against a series of symmetric polystyrene–polybutadiene diblock copolymers of varying molecular weight. A simple linear combining rule accurately represents the results. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 2056–2069, 2001

Relaxations in lamellar polystyrene–polybutadiene diblock copolymer. Thermally stimulated depolarization current study

The samples of the polystyrene-polybutadiene (PSPB) diblock copolymers with lamellar structure were investigated by integral and partial thermally stimulated depolarization current (TSDC) measurements in the 160–303 K range, and compared to the analogous investigation performed on a homopolymer sample of polystyrene (PS). The current peak, which appeared at 187 K, was found to be a dipolar relaxation α peak caused by the glass transition in the PB phase. The space-charge relaxation, distributed in the 220–260 K range and split into two parts – denoted as β 1 and β 2, was attributed to the possible local motion of the phenyl rings in the PS phase. The current maxima of the β relaxations significantly increased and shifted to the lower temperatures in the copolymer samples due to the PS–PB interfaces. The occurrence of doubleness and the relative distance between β 1 and β 2 was discussed. The relative numbers of the relaxing dipoles ( N) vs. E a were approximated. The energy width ( ω) was significantly increased in the copolymers due to the released motions at the glass–liquid PS–PB interfaces.

The dynamics of symmetric polystyrene–polybutadiene diblock copolymer melts studied above and below the order–disorder transition using dynamic light scattering

This communication describes dynamic light scattering measurements on three low molar mass symmetric polystyrene–polybutadiene diblock copolymer melts. Above but close to the order–disorder transition, four modes contribute to the time-dependent correlation function. In the depolarized geometry there is a very fast, broad relaxation typifying the segmental reorientational dynamics and a slower, single-exponential mode related to chain orientation and stretching. In the polarized experiments two additional processes are seen: the heterogeneity mode related to the self-diffusion of individual copolymer molecules and a slow mode representing the translational diffusion of large (≂100 nm) clusters. Just below the order–disorder transition (ODT), the slowest mode is shifted to very long times. The heterogeneity mode gives rise to depolarized scattering below the ODT because of the anisotropy induced by the lamellar structure. With the lowest molar mass copolymer above the ODT, it could be seen that the amplitude of the mode related to chain orientation and stretching decreases the deeper the sample is in the disordered state. A new subtraction technique was used for data analysis.

Inclusion Compound Formed between a Poly(.epsilon.-caprolactone)-Polybutadiene Diblock Copolymer and Urea

Inclusion Compound Formed between a Poly(.epsilon.-caprolactone)-Polybutadiene Diblock Copolymer and Urea

Mechanical Properties of Blends of Crystallizable Polybutadienes Containing Amorphous Polybutadiene Diblock Copolymers

Abstract Tensile failure properties of syndiotactic 1,2 polybutadiene/trans 1,4 polybutadiene crystalline blends are improved by addition of 5–10% amorphous 1,2 polybutadiene/1,4 polybutadiene diblock copolymer. The effect of block molecular weight and microphase behavior of the diblock copolymer was investigated. Heterogeneous diblocks enhance blend properties to a greater extent than homogeneous diblocks. In blends with enhanced properties, percent coverage of interfacial surface area by diblock is on the order of 10%.