SEGMENTAL AND CHAIN DYNAMICS IN A DIBLOCK COPOLYMER MELT NEAR THE MICROPHASE SEPARATION TRANSITION

The dynamics of segmental and chain orientation in poly(styrene-b-isop rene) (P(S-b-I)) block copolymer with PI fraction f(PI) = 0.61, degree of polymerization N = 70 and chiN congruent-to 9 at 25-degrees-C (chi is the interaction parameter) were investigated by depolarized Raylei gh scattering (DRS) and dielectric spectroscopy (d.s.) over a broad te mperature range (240-370 K) in the disordered phase. Two distinct prim ary relaxation processes with vastly different timescales were associa ted with segmental orientation within PS- and PI-rich regions selectiv ely probed by DRS and d.s. techniques. The width of the distribution r elaxation function for the slow segmental process was found to increas e with decreasing temperature, whereas the freezing of the slow segmen tal fluctuations was observed for the first time within the time windo w of photon correlation spectroscopy. Compared with an equivalent PI h omopolymer chain, the first normal mode describing the end-to-end fluc tuation of the copolymer chain displayed slower time tau1 but similar amplitude deltaepsilon(N)/f(PI). The new experimental results were dis cussed in terms of the fluctuation picture of block copolymers in the disordered melt, the chain conformation and the friction coefficient r atio of the foreign blocks.