RELAXATION PROCESSES IN A HOMOGENEOUS DIBLOCK COPOLYMER AT LOW AND HIGH-TEMPERATURES BY MEANS OF DYNAMIC LIGHT-SCATTERING

Photon correlation spectroscopy has been employed to probe the segmental dynamics of a low molecular weight homogeneous diblock copolymer of 1,4-isoprene and 1,2-butadiene and of its corresponding homopolymers above T(g). The experimental autocorrelation functions have been analyzed in terms of the function exp(-t/tau)beta to obtain the relaxation time, tau, and the exponent, beta. It has been found that while values of beta in the range 0.33-0.44 can satisfactorily fit the homopolymer density autocorrelation functions close to and above T(g), the corresponding beta of the copolymer data assumes a value 0.22 +/- 0.02. This finding, observed for the first time to the present authors' knowledge, implies a much broader spectrum of relaxation times for the copolymer. On the other hand, the dynamics of local density fluctuations at high temperatures studied by complementary Brillouin scattering measurements are quite similar in both diblock and 1,4-polyisoprene.