We have studied the time development of the molecular mass distribution (MWD) of living bifunctional poly(α-methylstyrene) in tetrahydrofuran after a quench to 21 K below the polymerization temperature Tp. We see an intermediate Gaussian distribution evolving toward a final exponential distribution, as expected from theoretical considerations. We see a longer equilibration time for the number average molecular mass (Mn) as well as for the mass average molecular mass (Mw) than for the monomer concentration ([M]), whereas theories predict that Mn and [M] will relax together and that Mw will take much longer.We have also studied the equilibrium MWD of this same system as a function of the average degree of polymerization (L). These measurements and the time study discussed above are the first experimental evidence that the equilibrium MWD for an organic polymer in a state of equilibrium polymerization is, indeed, an exponential/Flory-Schulz distribution, and is consistent with scaling predictions. We find that the bifunctionality of the polymer does not change the equilibrium MWD. However, near Tp and at low L, we observe a deviation from the exponential distribution, which may be evidence of the effect of a chain length dependence of the equilibrium constant for polymerization, or of the effects of polydispersity on correlations due to excluded volume.
Citation: Journal of Chemical Physics
Issue: No. 20
Pub Type: Journals
anion polymerization, Flory-Schulz distribution, living polymerization, molecular mass distribution, α-methylstyrene