Small angle neutron scattering, dynamic light scattering, and magnetic rheometry of the equilibrium polymer poly-alpha-methylstyrene in solution with tetrahydrofuran

Experimental study has been made of the equilibrium (living) polymer poly-{dollar}alpha{dollar}-methylstyrene in solution with tetrahydrofuran. Equilibrium polymers are those which have no termination step. For such polymers, there exists an equilibrium between polymer and free monomer, which depends on temperature. This equilibrium yields interesting physical behavior that was studied by several techniques. First, small-angle neutron scattering was used to study the polymerization of poly-{dollar}alpha{dollar}-methylstyrene in solution with tetradeuterofuran as a function of temperature and time. The scattering intensity, I(q,T), which is related to the concentration structure function, S(q,T), was measured as a function of the scattering vector, q. The results were extrapolated to q = 0, using the Omstein-Zernike expression, to obtain the zero-angle scattering intensity, I(0,T), and the characteristic length, {dollar}xi{dollar}(T). Results were compared to predictions from the mean field approximation of the n {dollar}to{dollar} 0 limit of the n-vector model of a magnetic phase transition and from the recently proposed dilute n {dollar}to{dollar} 0 theory. The observed maximum in I(0,T) was better predicted by the dilute n {dollar}to{dollar} 0 theory than by the mean field theory. The form of {dollar}xi{dollar}(T) was better described by the mean field theory than by the dilute n {dollar}to{dollar} 0 theory. The relaxation of I(0,T) as a function of time was observed to be faster for depolymerization than for polymerization for temperature jumps greater than or equal to 1 K. Second, dynamic light scattering was used, for the first time, to measure the autocorrelation function of living poly-{dollar}alpha{dollar}-methylstyrene in solution with tetrahydrofuran as a function of temperature. The diffusion coefficient as a function of temperature was determined from the autocorrelation function and was found to decrease as the temperature was increased. Finally, a magnetic rheometer was built and programmed for measuring viscoelastic properties of living polymer solutions.