CHAIN DIFFUSION IN THE MELT OF AN ASYMMETRIC DIBLOCK COPOLYMER IN THEDISORDERED AND ORDERED STATE

The self-diffusion in a polystyrene-b-polyisoprene diblock copolymer w ith a strongly asymmetric composition was investigated with dependence on temperature by pulsed field gradient (PFG) NMR. The diblock shows with decreasing temperature a disorder-to-order-transition at T-ODT = 393 K from a micellar liquid-like to a bcc ordered state which was rec ently measured by SAXS [M. Schwab and B. Stuhn, Phys. Rev. Lett. (1996 ) 76: 924]. Two diffusivities were observed, one of the free diblock c hains and one of the diblock chains fixed in micelles. The volume frac tion of free chains decreases with decreasing temperature. The diffusi vity of the free chains must be related to chain stretching. The exper iments show that within the time of the NMR experiment (300 ms) there is no exchange between the diblock chains in the free state and those fixed in the core of the micelles.