Macromolecular Architecture Effects on Block Copolymer Dynamics: Linear Tetrablocks and Inverse Starblocks

Abstract

Photon correlation spectroscopy and pulsed-field-gradient NMR have been used to investigate the role of different macromolecular architecture on the dynamics of block copolymer solutions in the low wavevector (q) limit using linear tetrablock (TB) and inverse starblock (SB) copolymers composed of two jointed TB's (N SB = 2N TB ). The three relaxation processes observed for diblocks are also evident in the present case: the cooperative diffusion, the internal copolymer chain relaxation (q 2 -dependent intensity and q-independent rate), and the polydispersity diffusive mode, controlled by the self-diffusion (due to the finite composition polydispersity). The internal mode 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 architecture. 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 architecture.