1,4-Polybutadiene behavior

The particle size of the dispersed phase depends upon the viscosity of the elastomer-monomer solution. Preferably the molecular weight of the polybutadiene elastomer should be around 2 x 10 and should have reasonable branching to reduce cold flow. Furthermore, the microstructure of the elastomer provides an important contribution toward the low-temperature impact behavior of the final product. It should also be emphasized that the use of EPDM rubber [136] or acrylate rubber [137] may provide improved weatherability. It has been observed that with an increase in agitator speed the mean diameter of the dispersed phase (D) decreases, which subsequently levels out at high shear [138-141]. However, reagglomeration may occur in the case of bulk... 

Another example of such a behavior is provided by the interesting polymerization of butadiene molecules imprisoned in tubes of clathrates of urea.9 Of course, the configuration of the resulting polymer is strongly influenced by the order introduced in the assembly of monomers and thus all trans polybutadiene is formed. 

The influence of ambient aging at 70°F and accelerated aging at 160°F on the stress-strain behavior of carboxy-terminated polybutadiene, polybutadiene-acrylic acid, polybutadiene-acrylic acid-acrylonitrile, and hydroxy-terminated polybutadiene composite propints is shown in Figures 10 and 11. The elastomers and curative agents for these formulations are listed below... 

Unlike polybutadiene, polyisoprene prepared at low temperatures shows little or no inclination to crystallize either on stretching or cooling. This may seem surprising in view of the even greater preponderance of trans-1 4 units in polyisoprene than in poly butadiene. The explanation for the contrasting behavior in this respect between low temperature synthetic polyisoprene, on the one hand, and guttapercha and low temperature polybutadiene, on the other, probably is to be found in the appreciable occurrence of head-to-head and tail-to-tail sequences of 1,4 units of the former. 

One characteristic of shear banded flow is the presence of fluctuations in the flow field. Such fluctuations also occur in some glassy colloidal materials at colloid volume fractions close to the glass transition. One such system is the soft gel formed by crowded monodisperse multiarm (122) star 1,4-polybutadienes in decane. Using NMR velocimetry Holmes et al. [23] found evidence for fluctuations in the flow behavior across the gap of a wide gap concentric cylindrical Couette device, in association with a degree of apparent slip at the inner wall. The timescale of these fluctuations appeared to be rapid (with respect to the measurement time per shear rate in the flow curve), in the order of tens to hundreds of milliseconds. As a result, the velocity distributions, measured at different points across the cell, exhibited bimodal behavior, as apparent in Figure 2.8.13. These workers interpreted their data... 

Water, methanol, and n-hexane do not influence the photooxidation of PVC (43), but the photodegradation is accelerated by ferric chloride (70,71) and certain other compounds containing iron (70,71,72). Purification of the polymer might be expected to enhance its photostability by removing deleterious impurities such as iron compounds that are derived from metal equipment. This type of result was obtained in one recent study (58) but not in others (30,59). In contrast, the photo-oxidative degradation of PVC should be enhanced by admixture of the polymer with materials that are unusually susceptible to photooxidation themselves. Such behavior has been observed for impact-modified PVC containing polybutadiene-based polyblends (69,73). 

The polybutadienes prepared with these barium t-butoxide-hydroxide/BuLi catalysts are sufficiently stereoregular to undergo crystallization, as measured by DTA ( 8). Since these polymers have a low vinyl content (7%), they also have a low gl ass transition temperature. At a trans-1,4 content of 79%, the Tg is -91°C and multiple endothermic transitions occur at 4°, 20°, and 35°C. However, in copolymers of butadiene (equivalent trans content) and styrene (9 wt.7. styrene), the endothermic transitions are decreased to -4° and 25°C. Relative to the polybutadiene, the glass transition temperature for the copolymer is increased to -82°C. The strain induced crystallization behavior for a SBR of similar structure will be discussed after the introduction of the following new and advanced synthetic rubber. 

The main conclusions of the strain induced crystallization behavior of high trans polybutadiene based rubber and natural rubber are (1) the rate of crystallization is extremely rapid compared to that of NR (2) the amount of strain induced crystallization is small compared to that of NR, especially at room temperature and (3) for the high trans SBR s relative to NR, crystallization is more sensitive to temperature at low extension ratios, and crystallization is less sensitive to strain. 

The stress relaxation properties of a high molecular weight polybutadiene with a narrow molecular weight distribution are shown in Figure 1. The behavior is shown in terms of the apparent rubber elasticity stress relaxation modulus for three differrent extension ratios and the experiment is carried on until rupture in all three cases. A very wide rubber plateau extending over nearly 6 decades in time is observed for the smallest extension ratio. However, the plateau is observed to become narrower with increasing extension... 

Schwahn, D. Willner, L. Phase Behavior and Flory-Huggins Interaction Parameter of Binary Polybutadiene Copolymer Mixtures with Different Vinyl Content and Molar Volume. Macromolecules 2002,35, 239-247. 

The high-pressure phase behavior of polymer-solvent-supercritical carbon dioxide systems was investigated experimentally The polymers used were poly(methyl methacrylate), polystyrene, polybutadiene, and poly(vinyl ethyl ether) at concentrations ranging from 5 to 10% in mixtures with toluene or tetrahydrofuran. The experiments were conducted for temperatures from 25 to 70°C and pressures up to 2200 psi in a high-pressure cell (Kiamos and Donohue, 1994). 

Propellants based on carboxyl-terminated polybutadiene characteristically exhibit the highest values of specific impulse which have been achieved for ammonium perchlorate-based composites. These propellants also exhibit satisfactory mechanical behavior over a wide range of temperatures and can be adjusted to meet the burning rate requirements of most applications. 

Generally applicable mathematical representations of the dilational behavior of propellants have not been developed, as might be expected however, Fishman and Rinde (29) have derived empirical expressions for the formulations which they studied. These relationships give reasonable description of uniaxial behavior over wide ranges of strain, time, and temperature for several testing modes. Equation 1 is representative of one of the generalized expressions for the polyurethane and polybutadiene formulations studied. 

Materials and Methods. The isomeric compositions of the four polybutadienes used are listed in Table I. Samples were prepared for infrared measurement from solutions of the polymer without further purification. Most films were cast from carbon disulfide solutions on mercury or on glass plates, but a few films were cast from hexane solutions to determine whether or not the solvent affected the radiation-induced behavior. No difference was observed for films cast from the different solvents. The films were cured by exposure to x-rays in vacuum. (Doses were below the level producing detectable radiation effects.) They were then mounted on aluminum frames for infrared measurements. The thicknesses of the films were controlled for desirable absorbance ranges and varied from 0.61 X 10 s to 2 X 10 3 cm. After measuring the infrared spectrum with a Perkin-Elmer 221 infrared spectrophotometer, the mounted films were evacuated to 3 microns and sealed in glass or quartz tubes (quartz tubes only were used for reactor irradiations). 

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