Dynamic mechanical properties and creep of poly- n-dodecyl methacrylate

Abstract

The real ( J′) and imaginary ( J″) components of the complex compliance have been measured between 24 and 3600 cycles/sec. in the temperature range from −40° to 45° C. for a fractionated poly- n-dodecyl methacrylate with molecular weight 0.95 × 10 6. The creep compliance, J( t), was measured from −30° to 30°C. The method of reduced variables gave superposed curves for J′ and J″ against frequency and for J( t) against time except for an anomaly at and below −28°, interpreted as due to crystallization of the side groups. The temperature dependence of relaxation times followed the WLF form with α f (thermal expansion coefficient of free volume) = 3.7 × 10 −4 deg. −1. The retardation and relaxation spectra, combining dynamic and creep data, show a rudimentary plateau region from which the average spacing between entanglement points is estimated to correspond to a degree of polymerization of 650. The logarithm of the monomeric friction coefficient (in dynes-sec./cm.) is −6.57 extrapolated to 100°C. The dependence of friction coefficient on side group length in the methacrylate series, using revised data including now those for the dodecyl polymer, can be rather satisfactorily attributed to differences in free volume by either the treatment of Dannhauser, Child, and Ferry or that of Fujita and Kishimoto.