Low temperature mechanical relaxation in poly- p-xylylenes

Abstract

The mechanical relaxation behaviour of poly- p-xylylene, poly(chloro- p-xylylene) and poly(dichloro- p-xylylene) has been investigated by means of an inverted torsion pendulum apparatus. Values are given for the shear modulus and loss for each of these three polymers at various temperatures from 80 K to room temperature. It is found that the unsubstituted poly- p-xylylene, even though it contains only two CH 2 sequences in its chain between phenylene units, exhibits a strong, low temperature relaxation process with a loss maximum at 159 K (0.54 Hz). The mono-substituted polymer, poly(chloro- p-xylylene), shows no loss peak in the 150 K region but does exhibit a damping maximum at 254 K (0.40 Hz). For the di-substituted polymer, poly(dichloro- p-xylylene), the loss modulus peak is again found in the low temperature region, being situated at 150 K (0.34 Hz). The data, together with other experimental observations, suggest that local reorientational motions of the phenyl, or substituted phenyl units, are involved in these secondary relaxation processes.