Polymer molecules containing chemically dissimilar segments have been investigated for many years. Their synthesis and characterization are challenging, and it is evident that their properties are often unusual and useful as witnessed by several books and reviews published on block and graft polymers. In this article we intend to review parts of this rapidly expanding area of polymer research of particular interest in rubber chemistry and technology, namely linear elastomeric block polymers. Sometimes the literature specifies the elastomeric nature of the products, on other occasions it does not. We have arbitrarily included those monomer combinations in which at least one monomer is known to form rubbery homopolymer. Urethan elastomers have been excluded because they have been extensively described elsewhere. In the broadest sense, block polymers are molecules in which two or more chemically dissimilar segments are joined end to end, a feature which distinguishes them from graft polymers. Each segment or block is usually a long sequence of units of a single monomer (A or B or C, etc.), but it may also be a long sequence of randomly copolymerized units (A plus B or C, etc.). Both types are known.
synopsisTri-and tetrachain radial polybutadienes have been synthmized by coupling very dilute solutions of linear polybutadienyllithium with stoichiometric smounts of methyltrichlorosilane or silicon tetrachloride. These polymem have three or four long chaiins (100-2000 carbon atoms) attached to a single atom.
Information concerning the synthesis of linear polybenzoylbenzoic acids of type I is sparse. Koelsch and Bryan2 prepared dibasic acids (la, n la, R = COOH
The physical properties of polybutadiene vulcanizates have been measured as a function of polymer microstructure. Although the over-all properties of any one polybutadiene are determined by the relative ratio of cis, trans and vinyl units in the polymer chain, marked changes in physical properties do not occur until a relatively pure configuration is approached or unless the raw polymer displays crystallinity. Thus, polybutadienes containing more than 85 per cent cis, trans or vinyl units are characteristically different from each other and the differences are accentuated as the isomeric forms approach 100 per cent of a given configuration. Polybutadiene of 95 per cent cis configuration displays very low heat generation and high resilience (equaling natural rubber in these properties) and excellent abrasion resistance. trans-Polybutadiene (90 per cent), a crystalline plastic in the raw state, becomes rubbery after vulcanization. Gum vulcanizates possess high tensile strength, and tread stocks display high modulus and tensile strength, high hardness and fair hysteresis properties. Vulcanizates of amorphous 94 per cent vinyl polybutadiene are characterized by fair tensile properties, low hysteresis, and poor low temperature properties. Crystalline syndiotactic polybutadiene, 70 per cent vinly, displays much higher gum and tread tensile strengths than its amorphous counterpart. Amorphous polybutadienes containing less than 70–80 per cent of any one configuration are generally similar in most properties, and resemble emulsion polybutadiene in many respects. The wide range of properties of the various polybutadienes makes them suitable for many applications. cis-Polybutadiene is an excellent tire rubber, which has given as much as 40 per cent greater abrasion resistance than natural rubber in passenger tire tests. Heavy duty 10:00 × 20 truck tires fabricated with a 1:1 blend of cis-polybutadiene and natural rubber in the treads have given slightly better abrasion ratings and lower running temperatures than control tires fabricated entirely from natural rubber. Amorphous 80 per cent cis-polybutadiene has been found to possess exceptionally good low temperature properties, far superior to present arctic-type unsaturated elastomers, trans-Polybutadienes by virtue of their high modulus, high tensile strength, and high hardness could be utilized in the preparation of hard rubber goods, floor tiles, and shoe soles. While none of these polybutadienes is yet available commercially, their unusual properties and potential applicability in many areas should lead to their manufacture in the future.
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