Brillouin scattering and dielectric relaxation in PPG of different chain lengths and end groups

We have investigated the structural relaxational behavior of poly(propylene glycol), PPG, for polymer chains of increasing number of monomer units, n( = 3, 7, 70), and for different end groups (OH and CH3) using Brillouin scat tering and dielectric relaxation. In the case of the OH capped systems the relaxation dynamics are rather insensitive to chain length variations, wher eas large effects are demonstrated when changing to CH3 end groups. For cha ins with n less than or similar to 20, there is a radical decrease in the s ound velocity and the average relaxation time, when the hydroxyl terminatio ns are replaced by methyl terminations. By using the nonpolar CH3 endcappin g the linking of adjacent chains, as is the case in the hydrogen bonded OH capped systems, is avoided. (C) 1999 Elsevier Science Ltd. All rights reser ved.