Dielectric Relaxation Spectroscopy of Gradient Copolymers and Block Copolymers: Comparison of Breadths in Relaxation Time for Systems with Increasing Interphase

Two series of styrene/n-butyl acrylate (S/nBA) gradient copolymers and block copolymers are prepared with a range of molecular weights to investigate the effect of increasing interphase on relaxation time distributions and to relate these to measurements of glass transition breadth using differential scanning calorimetry and dielectric relaxation spectroscopy (DRS). This is the first time DRS has been used in the study of gradient copolymers. The segmental relaxation associated with the dielectrically active component of the block copolymers (nBA) resembles that of poly(n-butyl acrylate) in behavior but becomes broader as the system shifts from highly segregating to moderately segregating. In contrast, the gradient copolymer segmental relaxation largely resembles that of a random copolymer with similar composition but with broader relaxation time distributions. The one exception is the most phase-segregated of the gradient copolymers, for which the relaxation response appears as two overlapping contributions representing regions of high nBA content and low nBA content. The breadth in relaxation time achieved by this gradient copolymer is comparable to or exceeds that of a weakly segregated block copolymer.