Effect of vinyl content on self-diffusion in polybutadiene melts

Diffusion coefficients, D, have been measured at five temperatures for melt s of 14 samples of polybutadiene with varying vinyl content, f(v), covering a broad range. Seven of the samples have a molecular weight, M, near 1300, and the other seven have M near 3400. The experiments show that D tends to decrease with increasing f(v). This trend in the experiments can be ration alized by two seemingly different approaches. One successful approach utili zes free volume theory. The other successful approach is a Monte Carlo simu lation that employs different jump rates for beads representing the two typ es of butadiene units. The two methods may not be as different as they appe ar initially, because they both incorporate, directly or indirectly, the fa ct that the glass transition temperature moves closer to the temperature us ed for measurement of D as f(v) increases.