RHEOLOGY OF THE LOWER CRITICAL ORDERING TRANSITION

Linear viscoelastic dynamic theological measurements were performed on symmetric diblock copolymers of deuterated polystyrene and poly(n-but yl methacrylate), denoted P(d-S-b-nBMA). Isothermal frequency sweep da ta were time-temperature superposed. A transition from a disordered to ordered morphology was found with increasing temperature as a functio n of molecular weight. P(d-S-b-nBMA) with molecular weights less than 6.8 x 10(4) were always disordered, as evidenced by the scaling of the storage and loss moduli with frequency at low frequencies, G' proport ional to omega(2) and G' proportional to omega. Copolymers with molecu lar weights above 9.9 x 10(4) were always ordered, exhibiting very lon g relaxation times and appearing almost solidlike in the low-frequency limit. Mixtures of the 6.8 x 10(4) and 9.9 x 10(4) copolymers, howeve r, showed a transition from fluid to solidlike behavior as the tempera ture was increased. This theological data is consistent with the exist ence of a lower critical ordering temperature, LCOT, where a transitio n from a disordered to ordered state occurs with increasing temperatur e.