Macromolecular architecture effects on block copolymer dynamics: Linear tetrablocks and inverse starblocks

Photon correlation spectroscopy and pulsed-field-gradient NMR have been use d to investigate the role of different macromolecular architecture on the d ynamics of block copolymer solutions in the low wavevector (q) limit using linear tetrablock (TB) and inverse starblock (SB) copolymers composed of tw o jointed TB's (N-SB = 2N(TB)) The three relaxation processes observed for diblocks are also evident in the present case: the cooperative diffusion, t he internal copolymer chain relaxation (q(2)-dependent intensity and q-inde pendent rate), and the polydispersity diffusive mode, controlled by the sel f-diffusion (due to the finite composition polydispersity). The internal mo de characteristics are identical for both systems at a given concentration, in agreement with theoretical estimates for Rouse chains, whereas the self -diffusivities show the effect of the total molecular weight and the archit ecture. At high concentrations of the SB copolymers, there is evidence for an extra relaxation process with a strong-concentration-dependent intensity apparently due to the proximity to the ODT and due to the macromolecular a rchitecture.