Polybutadiene samples, composition

Comparison of the loss modulus data for three blend compositions of the two polybutadiene samples in Fig. 9.23 at 30 C with the predictions of... 

Polybutadiene samples prepared by anionic polymerization contain a random distribution of cis-1,4, trans-1,4 and vinyl-1,2 units. Draw stmctures of a portion of polymer chains consisting of approximately 20 nnits for PB samples of the following composition ... 

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). 

We have performed such calculations for samples of non-functional polybutadienes 66) (Fig. 11) and, using the found Ax and X0 values, we calculated Kd0) for a cubic lattice model and a slit-like pore within the whole experimentally accessible eab range using Eq. (3.16). The result presented in Fig. 12 shows a good agreement of the experimental data with the calculated curves. Even such a crude model as the lattice-like model and a slit-like pore can be successfully applied to assess the change in the retention volume as a function of the composition of the mobile phase. 

Let us now turn again to the problem of the thermodynamic quality of the solvent. In the above examples, the solvent quality was different. Thus, for PDEGA in the hexane — MEK mixture, only MEK. is good on the contrary, for polybutadienes hexane is a good solvent. In the chloroform-acetone mixture both solvents are good for PDEGA. Thus, the use of solvents with a different thermodynamic quality in binary mixtures has no qualitative effect on separation it is only necessary that the sample should be readily soluble in binary mixtures whose composition is close toC. ... 

When only spectroscopic methods are used, they are able to identify polymer components with respect to their chemical nature. However, in many cases, they are unable to answer the question whether two chemical structures are combined to yield a copolymer or a blend or both. For example, analyzing a rubber mixture one is able to identify styrene and butadiene as the monomer units. However, using FTIR or NMR it is impossible to decide if the sample is a mixture of polystyrene (PS) and polybutadiene (PB),or a copolymer of styrene and butadiene, or a blend of a styrene-butadiene copolymer and PB. For the latter case, even the copolymer composition cannot be determined just by running a FTIR or NMR spectrum. 

A detailed study of SB diblock copolymers and diblock/homopolymer blends was conducted in the range of composition in which the polybutadiene cylindrical morphology prevails Stress-strain experiments on a series of samples revealed dramatically varying behavior from essentially brittle response to substantial and attractive levels of toughness. Figures 2a to 2d provide representative stress-strain curves for the initial morphologies shown in Figs. 3a-3d. Table 1 provides the relevant molecular level information for these blends. 

We have examined the microstructure of a number of dichlorocarbene adducts of both cis- and trans-polybutadiene using 13C NMR spectroscopy. Samples were prepared in a two phase system where dichlorocarbene was generated by the reaction of either concentrated aqueous or solid alkali metal hydroxide with chloroform in the presence of a phase transfer catalyst (14t). Monomer compositions and sequence lengths were obtained as for true copolymers and were correlated with glass transition temperature and phase morphology. 

The analysis of the obtained results shows that fiber-reinforced RubCon is a composite hydrophobic material with a coefficient of water resistance of Kcr = 0.995. Decreasing compressive strength was not observed and water absorption was 0.05% on weighing of samples. The small change of weight is due to the hydrophobic surface of RubCon. This is due to the intrinsic properties of the polybutadiene binder, which is not moistened with water. Furthermore, polybutadiene oligomer is nonpolar liquid. 

Spherical micelles with a polybutadiene core were formed for a certain range of compositions of the mixed solvent. The equilibrium between micelles and nonas-sociated macromolecules was found to be consistent with a closed association mechanism. In comparison with a linear triblock copolymer, the star-block sample showed a lower aggregation number. 

Fig. 8a. Scaling behavior of qm(t) vs the rescaled time f = tD q (0) = 2X(0) [XsM>o) — 3 for the polymer mixture as shown in Fig. 6a and a quench to T = 25 °C. Different symbols refer to different sample geometries. The solid curve is a fit to a formula ohtained by Furukawa [168] corresponding data for polyvinylmethylether (PVME)-polystyrene (PS), dash-dotted [158] and cyclohexane/meth-anol, dashed curve [169], are included. From Bates and Wiltzius [36]. b Coarsening behavior of mixtures of SBR (a random copolymer of styrene and polybutadiene) and polyisoprene (PI) at various compositions, at T = 60 °C. a shows qm(t) and b. corresponding intensity I (t), in arbitrary units, while arrows indicate the times where pinning (t,) or crossover (t ) from intermediate to late stages occurs. From Hashimoto et al. [173]...

An ABS sample prepared in our laboratory was used to develop the separation technique. Its composition was (wt %) butadiene, 20 acrylonitrile, 21 and styrene, 59. The ABS powder was dispersed in methyl ethyl ketone (MEK) at 1 wt % concentration. MEK was chosen because it is a good solvent for styrene/acrylonitrile copolymers, it is a poor solvent for polybutadiene, and its density is lower than that of polybutadiene and therefore lower than the density of the graft copolymer. 

The characteristics of the samples used are summarized in Table 1 where SBR, PB and PI designate, respectively, a random copolymer of poly(styrene-random-butadiene), polybutadiene, and polyisoprene. Binary mixtures of PP/EPR (14), X-7G/PET (15), both having (50/50 wt/wt composition), and PS/SB (16) (35/65 w wt) were occasionally us, where PP, EPR, X-7G, PET, PS and SB, designate, respectively, isotactic poly(propylene), a random copolymer of... 

Fig. 18. The critical micelle concentrations of three styrene/butadiene diblock copolymer samples in the matrix of low molecular weight polybutadiene are plotted against temperature. The approximate compositions (stytene vs. butadiene) of the block copolymers are indicated.. (From Rigby and Roe )...

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