Vinyl polybutadiene

Carbon Cha.in Backbone Polymers. These polymers may be represented by (4) and considered derivatives of polyethylene, where n is the degree of polymeriza tion and R is (an alkyl group or) a functional group hydrogen (polyethylene), methyl (polypropylene), carboxyl (poly(acryhc acid)), chlorine (poly(vinyl chloride)), phenyl (polystyrene) hydroxyl (poly(vinyl alcohol)), ester (poly(vinyl acetate)), nitrile (polyacrylonitrile), vinyl (polybutadiene), etc. The functional groups and the molecular weight of the polymers, control thek properties which vary in hydrophobicity, solubiUty characteristics, glass-transition temperature, and crystallinity. 

Polybutadiene. The many forms that can result from the polymerisation of butadiene, depending on the catalysts used, include high cis, medium cis, low cis, and high vinyl polybutadiene (PBD) (see Elastomers, synthetic-polybutadiene). 

Several reports iu the Hterature describe the preparation and characterization of low, medium, and high vinyl polybutadienes (55—69). Each of these references used polar modifiers including chelating diamines, oxygenated ether compounds, acetals, ketals, and compounds of similar stmctures (56—64). 

In the mid-1970s there was a short period during which styrene was in very short supply. This led to the development of what were known as high-vinyl polybutadienes which contained pendent vinyl groups as a result of 1,2-polymer-isation mechanisms. These rubbers had properties similar to those of SBR and could replace the latter should it become economically desirable. 

Figure 1. Stress relaxation curves for three different extension ratios. Uncross-linked high-vinyl polybutadiene with a weight average molecular weight of 2 million and a reference temperature of 283 K. G is the apparent rubber elasticity modulus calculated from classical affine theory. (Solid line is data from Ref. 1).

The effect of cross-linking in the unstrained state is shown in Figure 4 for a high-vinyl polybutadiene with a molecular weight of... 

Firestone and Shell started commercial production of cis-polyisoprene by the anionic process in the 1950 s but these plants are no longer in operation now. About the same time, Phillips started the manufacture of polybutadienes by the anionic route and ever since, there has been a steady growth in their use, particularly in the tire-tread as well as tire-carcass formulations. These solution polybutadienes, generally, have low vinyl contents but recently, Phillips has found some interesting applications for medium vinyl polybutadienes as well.14 Polybutadienes with 50-55 percent vinyl contents behave like emulsion polymerized SBR in tire tread formulations and exhibit very similar tread... 

This versatility gives the synthetic polymer chemist a tool to tailor the chain of the polybutadiene to fit the desired application. It can be used to manipulate the low temperature properties important in rubber goods and tire applications. Moreover, the chemical reaction that chemists want to perform on these rubbers can be altered, depending on the reactivity of the 1,2 polybutadiene double bonds fraction versus that of 1,U polybutadiene. The work of Halasa and co-workers (21) illustrates this point. These workers hydrogenated medium vinyl polybutadiene (1,2 content varied between 60-60%... 

In the amorphous tram- and the side vinyl polybutadienes, the first-order reaction rate constants (Table III) give high initial yields (G0) for olefin disappearance when the initial concentration is inserted in the rate equation kD = n(CJCD), where k = rate constant, C = initial concentration, and CD = concentration after dose D. The activation energies for the disappearance of both these olefinic species range from 3.4 to 4.0 keal. per mole, not very different from the activation energy observed for cis disappearance. 

The first-order rate constants for terminal vinyl groups and for trans-vinylene groups in linear polyethylene were observed by Dole and Williams (8) to be 20 to 30 times higher than our corresponding rates in the amorphous trans- and vinyl polybutadienes (Table III). On the other hand, the initial yields were lower than our G0 values because of the... 

The light-scattering apparatus and procedure have been formerly described (15). The only modification and precaution with polybutadienes were to use the appropriate refractive index differential for each polymer as this was observed to decrease with vinyl content values used were 0.118, 0.112, and 0.106 dl/gram for 2, 10, and 20% vinyl polybutadienes in cyclohexane at 25 °C and 546 m//,. 

Figure 10. Electron micrographs of (a) a 50/50 blend of IR and high-cis polybutadiene and (b) a 50/50 blend of medium-cis poly butadiene and high-vinyl polybutadiene. See Table 111 for details of diene microstructures.

WLF parameters are for cis-trsns-vinyl" polybutadiene from Ferry (1980). t WLF parameters are for Hevea rubber from Ferry (1980). 

Polymers that contain a double bond in their backbone (that cannot rotate) can exhibit structural isomerism. Such polymers have distinct structural isomers, such as cis, trans-, and vinyl-polybutadiene shown in Fig. 1.3. These isomers result from the different ways that dienes, such as butadiene, can polymerize and many synthetic polymers have mixtures of cis and trans structural isomers along their chains. A particular mixture reflects the probabilities of various ways that monomers add to the growing chain. 

Takeuchi, Y. Yoshimura, Y. Ohshima, N. Sakakibara, M. High Vinyl Polybutadiene or Styrene-Butadiene Copolymer. U.S. Patent 4,397,994, Aug 9, 1983 Japan Synthetic Rubber. 

These properties determine how carbon black will be distributed within the blend. These properties are not those of the filler but are the essential properties of the matrix. The matrix thus has strong influence on particle distribution. SEM studies showed that high vinyl polybutadiene and styrene-butadiene copolymers had morphologically identical carbon black distribution. However, their mechanical properties were very different. NMR analysis indicated that the difference in mechanical behavior is related to the interaction and more precisely to the molecular motions in rubbery matrix. 

Sulfur, or the so-called coagents (Loan, 1963 Lenas, 1964), can be used to suppress scission. Examples of coagents are m-phenylenebismaleimide, high-1,2 (high-vinyl)polybutadiene, triallyl cyanurate, diallyl phthalate, and ethylene diacrylate. Their mechanism of action may be as follows ... 

Peng, Z. L., Olson, B. G., Srithawatpong, R., McGervey, J. D., Jamieson, A. M., Ishida, H., Maier, T. M., and Halasa, A. R, Study of free volume in high vinyl-polybutadiene/cis-polyisoprene blends by positron annihilation lifetime spectroscopy, J. Polym. Sci. Polym. Phys., 36, 861-871 (1998). 

The compound n-butyllithium was the initiator and cyclohexane the solvent for high-vinyl polybutadienes produced from anionic polymerisation. Complexing... 

No.2,1991,p.338-42 RAMAN SPECTROSCOPIC CHARACTERISATION OF HIGH-VINYL POLYBUTADIENES PRODUCED FROM ANIONIC POLYMERISATION Poshyachinda S Edwards H G M Johnson A F BRADFORD,UNIVERSITY... 

---