Polybutadienes made with six different catalyst systems were examined: (1) butyllithium, (2) “nickel-based”, (3) alfin, (4) “titanium-based”, (5) “cobalt-based”, and (6) free radical emulsion. The microstructure and macrostructure of the polybutadienes have been determined and are compared to the results published in the literature. These polybutadienes may be considered to be random terpolymers of cis, trans, and vinyl addition of butadiene. The glass transition temperature is specified by the vinyl content. The crystalline melting points of the high trans and also the high cis polybutadienes obey to a high measure Flory's equation for melting point depression of a random terpolymer. The molecular weights of the polybutadienes have been determined by light scattering and osmometry and the degree of long chain branching has been determined by the branching index, 〈g′〉. The macro-structural features of the linear polymers are confirmed by fractionation. However, the polydispersities calculated from fractionation data do not agree with those determined from light scattering and osmometry for the branched samples. The discrepancy is attributed to the method of characterization of the fractions. A distinction is made between molecular weight distribution and molecular size distribution.

A new flex testing machine has been developed which yields accurate information on cut growth of vulcanizates. Its unique features are accurate temperature control of the test chamber (25°–200° ± 1° C), adjustable work input upon the test specimen by varying both the frequency of flexing (100–600 ± 1 rpm) and flex angle, and accomodation of a large number of test specimens (90–120). Furthermore, provision is made to test with a specific testing atmosphere, either oxidative or inert, depending on the required severity of conditions. Advantages of the test machine are: a) simple operation, once the test conditions are established: b) rapidity of testing, since a large number of specimens can be tested at the same time; and c) excellent reproducibility in preparing test specimens, varying and maintaining test conditions, and measuring cut growth. The maximum standard error for the test is about 12%. A further advantage is that compounds of varying degrees of hardness, for example, tire treads, shoe soles, and belt compounds, can be tested on the same machine by adjusting the severity of the test conditions. Effects of polymer and compounding variables on cut growth are discussed using data obtained with this new flexing machine.