Molecular Structure of Styrene-Butadiene Copolymers. Dynamic Mechanical Measurements

The dynamic shear modulus, mechanical damping, swelling properties in benzene, and infrared spectra have been determined on a series of styrene-butadiene copolymers which were prepared under a variety of polymerization conditions. Evidence is presented which indicates it may be possible to prepare a poly-butadiene rubber which retains its rubberlike properties down to −120° C. Materials of the same overall composition were often found to differ greatly in structure as determined by these experimental methods. Many of these differences can be explained in terms of various types of heterogeneity found in the copolymers. The temperature of maximum mechanical damping is primarily determined by the composition of the copolymer, whereas the width of the damping peak is related to the heterogeneity of the material. The work reported here is part of an investigation of the differences in physical properaties of polymers of like composition that occur as a result of changes in polymerization conditions.