Low vinyl content

Polyisoprene can be UV or e-beam cured [43,44]. The 3,4 units are particularly prone to crosslinking at low dose [45]. SIS and SBS are also crosslinkable, even conventional linear materials with low vinyl content however, small amounts of liquid trithiol or triacrylate compounds speed cure dramatically [44]. Like UV, e-beam cure is strongly affected by tackifier choice. Hydrogenated, non-aromatic resins provide much less interference with cure [36,37]. 

Thus, this polymerization catalyst yields more random copolymers with styrene, while still maintaining a low vinyl content and high trans-1,4 content. 

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. 

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... 

However, if both ends of the polymer, or the ends of a star branched polymer should have a high vinyl content and the remaining segments should have a low vinyl content, this method will not work because coupling reactions result in high vinyl in the center of the polymer chain or star branched polymer. 

Tg effects of low vinyl content SSBR / high vinyl content SSBR (75/25) blends... 

Introducing the measured Tg-values of 200.5 K for the low vinyl content SSBR/high vinyl content SSBR 75/25 (solution) blend and 217.5 K for the 25/75 (solution) blend of the same polymers resulted in an average Kl value of 0.41. Using this value for Kl, equation 1.6 can be written as ... 

HIPS) is produced commercially by the emulsion polymerization of styrene monomer containing dispersed particles of polybutadiene or styrene-butadiene (SBR) latex. The resulting product consists of a glassy polystyrene matrix in which small domains of polybutadiene are dispersed. The impact strength of HIPS depends on the size, concentration, and distribution of the polybutadiene particles. It is influenced by the stereochemistry of polybutadiene, with low vinyl contents and 36% d5-l,4-polybutadiene providing optimal properties. Copolymers of styrene and maleic anhydride exhibit improved heat distortion temperature, while its copolymer with acrylonitrile, SAN — typically 76% styrene, 24% acrylonitrile — shows enhanced strength and chemical resistance. The improvement in the properties of polystyrene in the form of acrylonitrile-butadiene-styrene terpolymer (ABS) is discussed in Section VILA. 

Retrospective View of Vinyl-BR Properties In the 1950s, the Phillips Petroleum Company and the Firestone Tire and Rubber Company started commercial production of polybutadienes by organolithium polymerization for use in tyres. These solution BRs, having low vinyl contents (8-10%), were used in blends with emulsion SBR in tyre treads for balancing traction and wear performance properties. In the early 1970s when styrene monomer was in short supply, developments from Phillips Petroleum Company and EniChem (formerly the International Synthetic Rubber Company) showed that vinyl-BRs with 50-55% vinyl content behaved like emulsion polymerized SBR in tyre tread formulations and exhibited very similar tread wear and wet skid resistance. Tread compounds containing 45%-vinyl polybutadiene showed lower heat build-up and better blow-out resistance than E-SBR and blends of E-SBR with cw-BR. EniChem introduced trial quantities of a medium-vinyl butadiene rubber (MVBR) under the name Intolene 50 in 1973. 

Polybutadiene (ER) is the second largest volume synthetic rubber produced, next to SER (Scheme 21.3). The major use of polybutadiene is in tires, with over 70% of the polymer produced going into treads and sidewalls. Cured ER imparts excellent abrasion resistance (good tread wear), and low rolling resistance (good fuel economy) due to its low glass transition temperature (T. The low Oower than -90 °C) is a result of the low vinyl content of polybutadiene. Due to the fact that the low leads to poor wet traction properties, polybutadiene is usually blended with other elastomers, such as natural rubber or SER for tread compounds. 

McGarey and Richards also found some evidence for a shoulder in their SANS studies from cross-poly(dimethylsiloxane)-inrer-cross-polystyrene sequential IPN s corresponding to a wavelength of 2500 A. This may have been the result of the very low vinyl content in their poly(dimethyl-siloxane). By other methods of analysis, they estimated chord lengths of the order of 200-500 A. Examination of the older literature, both by Sperling s group as well as others, suggests that spinodal decomposition plays an important part in domain formation of many IPN systems. 

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