Polystyrene/polybutadiene films

Kim, G. Libera, M. Microstructural development in solvent-cast polystyrene-polybutadiene-polystyrene (SBS) triblock copolymer thin films. Macromolecules 1998,31, 2569-2577. Bates, F.S. Polymer-polymer phase behaviour. Science 1991, 251, 898-905. 

First attempts to record the micro/nanomechanical surface properties with atomic force microscopy/scanning probe microscopy (AFM/SPM) probing were conducted by using the classical Sneddon s approach [1-3]. Further development lead to the micromapping of the surface mechanical properties with a force modulation mode [4-8]. Several studies were focused on the development of dc force-displacement probing of the micromechanical properties [9-15]. In this communication, we report on studies of the micromechanical properties of composite films of polystyrene/polybutadiene (PS/PB) and grafted PS layers and prove the feasibility of... 

A study of a PS-PB block copolymer showed variation in craze behavior as a result of rubber particles added to modify the otherwise brittle, glassy polymers. Such copolymers were studied under the high strain of physical laboratory testing where the polybutadiene in the copol)mier was stained with osmium tetroxide prior to microtomy [333]. The brittle behavior of the glassy polymers was shown by TEM and STEM to be modified by the rubber particles which provide toughening by control of the craze behavior. In a study of the craze behavior in isotactic polystyrene [146], films of polystyrene were drawn from dichlorobenzene solution and cast onto glass microscope slides, followed by... 

We calculated the microphases of a thin film of neat three-block polystyrene - polybutadiene - polystyrene (SBS) deposited on a solid substrate [33]. The parametrization protocol was somewhat different from the case of L64, now using data on the microphase-separation temperature of a bulk melt to determine the critical Flory-Huggins value, rather than solution data. 

The use of lightly crosslinked polymers did result in hydrophilic surfaces (contact angle 50°, c-PI, 0.2 M PhTD). However, the surfaces displayed severe cracking after 5 days. Although qualitatively they appeared to remain hydrophilic, reliable contact angle measurements on these surfaces were impossible. Also, the use of a styrene-butadiene-styrene triblock copolymer thermoplastic elastomer did not show improved permanence of the hydrophilicity over other polydienes treated with PhTD. The block copolymer film was cast from toluene, and transmission electron microscopy showed that the continuous phase was the polybutadiene portion of the copolymer. Both polystyrene and polybutadiene domains are present at the surface. This would probably limit the maximum hydrophilicity obtainable since the RTD reagents are not expected to modify the polystyrene domains. 

As shown in Figures 5 and 7 the nature of the solvent does not appear to have any effect on T0 within experimental error. However, the solvent can have a profound influence on the morphology of cast block copolymer specimens. Thus, instead of the continuous polybutadiene phase normally observed, a continuous polystyrene phase appears to exist in Kraton 101 films cast from solution in MEK/THF mixtures (2). Methyl ethyl ketone has a solubility parameter of 9.3, only slightly higher than that of the solvents used in our work. It is clear from the data presented here that our films must have had continuous polybutadiene phases. 

The concept of using block copolymers for preparation of nanoscopically structured material and surfaces was advanced further by introducing a third block in the chain structure [29]. One of the consequences of the multiphilicity and versatility of the ABC triblock copolymers is their tremendous richness and diversity in morphology. One of the most peculiar structures is shown in Fig. 28 where the helices of a polybutadiene microphase are wound around columns of polystyrene which are embedded in a matrix of polymethylmethacrylate. Complementary to the TEM studies of the bulk morphology (Fig. 28a,b), SFM has been used to image the surface structure of the triblock copolymer films. Figure 28c shows the wrapped PS cylinders oriented parallel to the surface, where one... 

The experimental studies on phase behavior and pattern formation reviewed here have been done on substrate-supported films of cylinder-forming polystyrene- foc -polybutadiene diblock (SB) [36, 43, 51, 111-114] and triblock (SBS) [49, 62, 115-117] copolymers (Table 1), lamella-forming polystyrene- /ocfc-poly(2-vinyl pyridine) diblock copolymers (SV) [118, 119] and ABC block terpolymers of various compositions [53, 63, 120-131], In simulation studies, a spring and bid model of ABA Gaussian chains has been used (see Sect. 2) [36,42, 58, 59],... 

The dynamic viscoelasticity and the thermal behaviour of films of Thermoelastic 125 cast from solutions in four solvents - toluene (T), carbon tetrachloride (C), ethyl acetate (E), and methyl ethyl ketone (M) — have been studied by Miyamato133 The mechanical loss tangent (tan 8) and the storage modulus E dependences exhibit two transitions at —70 °C and 100 °C which have been attributed to onset of motion of polybutadiene and polystyrene segments, respectively. The heights of the polybutadiene peaks on tan 6 curves decrease in the order C > T > E > M, while for polystyrene the order is reversed C < T < E < M. These phenomena have been related to the magnitude of phase separation of the polystyrene and polybutadiene blocks. 

Electron Microscopy. Figure 3 shows electron micrographs of ultra-thin sections of film specimens of the three kinds of block copolymers. As can be seen in the figure, TR-41-1647 and TR-41-1648 specimens have a heterogeneous structure in which the polystyrene domains are dispersed within a polybutadiene matrix and are connected to each other to form a swirl-like structure. On the other hand, TR-41-1649 specimen is seen to consist of alternating lamellar domains of the two components. Changes of the domain structure with fractional compositions of styrene and butadiene components are consistent with predictions of the current theories of micro-phase separation (12,13,14,15) for block copolymers cast from such a nearly nonselective solvent as the mixture of THF and methylethylketon (90/10 in volume ratio). 

The samples used in this study are listed in Table I with selected characterization data. Also given are our notations for the samples. S and B represent polystyrene and polybutadiene, respectively. The block polymers are denoted S/Bi, S/B2, etc. The letters identify the polymer components with the first letter indicating the center segment. The polymers were isolated from the polymerization solution by precipitation into cold (0°C), well-stirred methanol. After careful drying in a vacuum oven (25°C), film samples were prepared by melt pressing at temperatures ranging from 25 °C for homopolybutadiene to 150 °C for homopolystyrene. 

Only recently first reports appeared describing the potential of the nanostructured thin block copolymer films for lithographic etching. A thin film of polystyrene-block-polybutadiene with a hexagonal cylindrical morphology where the poly-(butadiene) cylinders were oriented perpendicular to the substrate was deposited on a silicon wafer and selectively decomposed by treatment with ozone or converted with osmium tetroxide. By a subsequent reactive ion etching process the pattern could be inscribed into the surface of the silicon wafer yielding small holes or islands with a lattice constant of 27 nm and hole/island sizes of 13 nm [305,312]. 

The diffusion coefficients of cyclohexane in an SBS block copolymer and of iso-octane in Sclair polyethylene demonstrated unique morphological structures within the polymers, The interphase between polystyrene domains and polybutadiene matrix in SBS TR-41-2443 was identified by the time-dependent nature of the diffusion coefficient. Curves of Mt/M plotted against for different film... 

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