1,4 Polybutadiene matrix

Figure B8.2.1 shows the fluorescence spectra of DIPHANT in a polybutadiene matrix. The h/lu ratios turned out to be significantly lower than in solution, which means that the internal rotation of the probe is restricted in such a relatively rigid polymer matrix. The fluorescence intensity of the monomer is approximately constant at temperatures ranging from —100 to —20 °C, which indicates that the probe motions are hindered, and then decreases with a concomitant increase in the excimer fluorescence. The onset of probe mobility, detected by the start of the decrease in the monomer intensity and lifetime occurs at about —20 °C, i.e. well above the low-frequency static reference temperature Tg (glass transition temperature) of the polybutadiene sample, which is —91 °C (measured at 1 Hz). This temperature shift shows the strong dependence of the apparent polymer flexibility on the characteristic frequency of the experimental technique. This frequency is the reciprocal of the monomer excited-state...

The situation is quite different with block copolymers. As an example we again take a copolymer of styrene and butadiene, but now as a three-block copolymer, SBS. The incompatibility of polystyrene and polybutadiene now results in a phase separation, which is enabled by the circumstance that the blocks can live their own life . The polystyrene chain ends clog together into PS domains, which lie embedded in a polybutadiene matrix. These glassy domains act as physical cross-links, so that the polymer has the nature of a thermoplastic rubber. The glass-rubber transitions of PS and BR both remain present in between these two temperatures the polymer is in a, somewhat stiffened, rubbery condition (see Figure 3.8). This behaviour is dealt... 

Inverse hexagonal structure. In the inverse hexagonal structure, the solvent is located in the cylinders. For solvent concentrations smaller than about 45%, cylinders of polystyrene arranged in an hexagonal array in a polybutadiene matrix are observed (see Fig. 22a, corresponding to a concentration of 30% of the added mono-... 

The mechanical properties of a macrolattice of SBS has been investigated (65). The sample consists of a hexagonal array of polystyrene cylinders embedded in the polybutadiene matrix. The stress-strain curves... 

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). 

Dynamic Mechanical Properties. Figure 15 shows the temperature dispersion of isochronal complex, dynamic tensile modulus functions at a fixed frequency of 10 Hz for the SBS-PS specimen in unstretched and stretched (330% elongation) states. The two temperature dispersions around — 100° and 90°C in the unstretched state can be assigned to the primary glass-transitions of the polybutadiene and polystyrene domains. In the stretched state, however, these loss peaks are broadened and shifted to around — 80° and 80°C, respectively. In addition, new dispersion, as emphasized by a rapid decrease in E (c 0), appears at around 40°C. The shift of the primary dispersion of polybutadiene matrix toward higher temperature can be explained in terms of decrease of the free volume because of internal stress arisen within the matrix. On the other... 

Finally Keller has developed a theory to explain the deformation behaviour of SBS copolymers with an hexr onal structure formed by polystyrene cylinders in a polybutadiene matrix. His theory, called Random-break treatment is based on a model consisting of a system of broken cylinders of the same initial length with the breaks distributed randomly along the cylinders. The author r ards the cylinders unstrained compared with the matrix material. He assumes the matrix to consist of small Hookean elements joining each rod to the six nearest rods and he calculates the stress in the cylinders due to the tensile strain of the matrix. The theoretical predictions are in a good agreement with the birefringence and electron microscopy results. 

Dual phase continuity offers many advantages, because rubber/plastic compositions yield tough, leathery materials. Many of the compositions described above, for example, contain two continuous phases, with cylinders of polystyrene meandering within the polybutadiene matrix. Since all IPN s are crosslinked, it may be that their greatest advantage will lie in products which are leathery or rubbery, but can not be permitted to flow. 

A structural model, based on a complex process of stretch induced ordering in the polyacetylene domains, was proposed to account for these observations. Support for this model was obtained using electron microscopic techniques. Low polyacetylene content blends (<20% PA) were found to consist of discrete polyacetylene domains dispersed in a continuous polybutadiene matrix. In the high polyacetylene content blends (>70% PA), both phases were simultaneously continuous, forming an interpenetrating network structure. Blends with intermediate compositions consist of both continuous and isolated domains of polyacetylene distributed throughout the polybutadiene matrix. 

Blending of polyacetylene with polybutadiene provides an avenue for property enhancement as well as new approaches to structural studies. As the composition of the polyacetylene component is increased, an interpenetrating network of the polymer in the polybutadiene matrix evolves from a particulate distribution. The mechanical and electrical properties of these blends are very sensitive to the composition and the nature of the microstructure. The microstructure and the resulting electrical properties can be further influenced by stress induced ordering subsequent to doping. This effect is most dramatic for blends of intermediate composition. The properties of the blend both prior and subsequent to stretching are explained in terms of a proposed structural model. Direct evidence for this model has been provided in this paper based upon scanning and transmission electron microscopy. 

Polymer Concrete Based on a Vulcanized Polybutadiene Matrix... 

Source Reprinted from O. Figovsky, Yu. Potapov, T. Makarova, and D. Beilin, Load-Carrying Capacity of Polymer Concrete with Polybutadiene Matrix, J. Scientific Israel Technological Advantages 4, no. 1-2 (2002) 21-24. With permission. 

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