Longitudinal Wave Relaxation of Poly (methyl acrylate) in Solution

Abstract

Recently, molecular motions of some vinyl-polymers in solution have been investigated by means of dynamic mechanical and dielectic methods. Masuda et al. reported that a molecular model of relaxation for PMA (low molecular weight)-acetone solution can be imagined in terms of the rotational isomer of a head-tail bond in the polymer chain, and for PMA (high M. W.)-acetone solution, a double relaxation was found in the same frequency region. A second relaxation for PMA (high M. W.)-acetone solution was related to the spreading of the polymer chain, on the basis of the solvent dependence of the relaxation processes.
In this study, the temperature dependence of the ultrasonic absorption and velocity for PMA (M_w=88×10⁴) in 1, 2-dichloroethane (good solvent) solution and also for PMA (M_w=108×10⁴) in toluene (poor solvent) solution were measured to investigate the difference between the thermal relaxation and the second relaxation. Double relaxation due to two kinds of molecular motion was found in the case of the high molecular weight PMA-toluene solution. It was concluded that one of them was a thermal relaxation due to the rotational motion of a chain segment, and the other was an order-disorder configuration transition based on the association of segments in a polymer sphere. A single relaxation was found in the low molecular weight PMA-1, 2-dichloroethane solution, the relaxation frequency of which has a transition temperature at 20°C. It was concluded that the molecular motion of the relaxation process below the transition temperature was that of the order-disorder configuration transition, as in the high molecular weight PMA-toluene solution.