Polybutadiene homopolymers

This combination of monomers is unique in that the two are very different chemically, and in thek character in a polymer. Polybutadiene homopolymer has a low glass-transition temperature, remaining mbbery as low as —85° C, and is a very nonpolar substance with Htde resistance to hydrocarbon fluids such as oil or gasoline. Polyacrylonitrile, on the other hand, has a glass temperature of about 110°C, and is very polar and resistant to hydrocarbon fluids (see Acrylonitrile polymers). As a result, copolymerization of the two monomers at different ratios provides a wide choice of combinations of properties. In addition to providing the mbbery nature to the copolymer, butadiene also provides residual unsaturation, both in the main chain in the case of 1,4, or in a side chain in the case of 1,2 polymerization. This residual unsaturation is useful as a cure site for vulcanization by sulfur or by peroxides, but is also a weak point for chemical attack, such as oxidation, especially at elevated temperatures. As a result, all commercial NBR products contain small amounts ( 0.5-2.5%) of antioxidant to protect the polymer during its manufacture, storage, and use. 

Tuzar and Kratochvil (23) have reported that styrene-butadiene block copolymers mlcellise in selective solvents for polystyrene and solubilise large amounts of polybutadiene homopolymer. Sinc.e the surface active grades of polyvinyl alcohol are polyvinyl alcohol-acetate block copolymers and water is a selective solvent for polyvinyl alcohol a similar effect may be expected which could affect the course of the vinyl acetate emulsion polymerisation. 

For completeness it should be pointed out that many interesting morphologies of the type described above can be obtained by polymerizing a solution of AB or ABA block copolymers in styrene monomer, analogous to the process of HIPS production in which polybutadiene homopolymer is the dissolved species. This approach has been described in detail by Echte... 

Polystyrene and polybutadiene homopolymers as well as random and block copolymers of these mers have been studied via dielectric relaxation spectroscopy and tensile stress-strain measurements. The results suggest that some block copolymer systems studied have styrene rich surfaces which appear to partially crosslink upon initial exposure to ozone even though surface oxygen concentrations are not significantly affected. After continued exposure these samples appear to then undergo chain scission. Complex plane analysis implies that after degradation... 

High molecular weight polybutadiene homopolymers are prepared conunercially with anionic catalysts and with coordinated anionic ones. Polybutadiene formed with sodium dispersions was prepared industrially in the former USSR, and perhaps might still be produced in that area today. This sodium-catalyzed polybutadiene contains 65% of 1,2-adducts. Most of the preparations by others, however, utilize either alkyllithium or Ziegler-Natta-type catalysts prepared with titanium tetraiodide or preferably containing cobalt. 

Discuss polybutadiene homopolymers. How are they prepared What are their uses ... 

It is important to mention that the studied styrene-butadiene copolymers and the polybutadiene homopolymer were synthesized by anionic polymerization. Therefore, just three isomers are possible to obtain, the 1,4-cis 1,4-trans and the 1,2-vinyl. 

The ultimate utility of any material lies in its performance. Let us examine now the types of reinforcement obtained with IPN s. Stress-strain curves for random (R) PB/PS IPN s are shown in Figure 8.22. As is well known, random cis-trans mixture) polybutadiene homopolymer is very weak, breaking at a rather low elongation. Both ultimate elongation and stress to break are increased by addition of the polystyrene network the work required to break, as measured by the area under the curves, is vastly increased. Further, the shapes of the curves are affected by the presence... 

The morphological structure of the butadiene-acetylene graft copolymer films was studied using TEM, electron diffraction and wide-angle X-ray scattering (WAXS). A series of the butadiene-acetylene copolymers with acetylene content ranging from 10 to 50 wt% and a cisitrans ratio from 70/30 to 10/90 was prepared [73]. Unreacted polybutadiene homopolymer was extracted from the copolymer samples in toluene... 

Figure 5.6 Morphology-induced dependence of the crystallization temperature (Tf) of the EO block on total polybutadiene (PB) concentration in binary blends of a polybutadiene homopolymer and a B-EO diblock copol5uner. Data obtained from a poly(ethylene oxide) homopolymer are included (dashed line) for reference. (Reprinted with permission from Chen, H.-L., Hsiao, S.-C., Lin, T.-L., Yamauchi, K., Hasegawa, H. and Hashimoto, T. Macromolecules 34 671, (2001). Copyright 2001 American Chemical Society.)...

Figure 6.7 Isothermal crystallization (67 °C) of strongly segregated sphere-forming E/SEB 9/ 55 monitored by time-resolved SAXS/ WAXS. Insets show the SAXS (left) and WAXS (right) patterns for E/SEB 9/55 both at the start (top trace in each panel) and end (bottom trace) of crystallization. E (110) peak intensity is shown as the lower data set (A), integrated SAXS intensity near q = 0.5nm is shown as the middle data set (O), both read on the left axis. Both are fit to first-order kinetics (solid curves) with half-times of 3 min. For comparison, the crystallization behavior of a hydrogenated polybutadiene homopolymer (E41) is shown as the top data set ( ), read on the right axis. The kinetics are qualitatively different (sigmoidal vs. first-order), and to achieve a similar half-time, a much higher crystallization temperature was required for E41 (95 vs. 67 °C). [Reprinted with permission from Loo et al. 2000a].

The modulus of hydrogenated polybutadiene homopolymers has been shown to be directly related to the 1-butene content in the polymer [11]. In the absence of... 

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