Dielectric normal mode relaxation of undiluted poly(propylene glycol)s

Dielectric measurements were carried out for linear and star-shaped poly(propylene glycol)s (PPGs) of different molecular weights (M). A small loss peak due to the normal mode relaxation was observed on the low-frequency side of the main loss peak. Two peaks were resolved and the normal mode relaxation time τn, the distribution of relaxation times and relaxation strength were examined. The effect of OH groups attached at the chain ends on the normal mode relaxation was also investigated by using PPG samples whose end groups were substituted by acetyl groups. The results indicate that τn is proportional to M2 in accordance with the Rouse theory. The mode distribution of star-shaped PPGs is slightly broader than that of linear PPGs. The effect of hydrogen bonding between the OH groups on the normal mode relaxation time is negligibly small.