We demonstrate that the poly(butyl acrylate) (PBA) elastomers containing considerable amounts of dangling chains with uniform lengths exhibit pronounced viscoelastic relaxation (tan δ > 1) at characteristic frequencies. The elastomers are obtained by the copolymerization of monoacryloyl- and diacryloyl-terminated precursor PBA with narrow size distributions. The molecular weights of the precursors are smaller than the critical molecular weight for the onset of entanglement coupling. The relaxation time of the elastomers (τD) is proportional to the square of the molecular weight of the dangling chains equivalent to the monofunctional PBA (M D), and τD is about 2.5 times larger than the relaxation time of the corresponding free guest chains in the elastomers (τG). These observations are close to the expectations from the Rouse-chain dynamics without entanglement effect (τD ∼ M D 2 and τD = 4τG). These results provide an important basis for the understanding of the dynamics of the unentangled chains whose one end is tethered to the permanent networks. The results also offer a route of molecular control of characteristic frequency and strength of mechanical damping of elastomers.

No abstract

Influences of vapors evaporated from an acryl-based non-silicone-type polymeric cured material and conventional silicone-containing polymeric cured materials were evaluated with respect to their effects on contact resistance characteristics of relay contacts at an ambient temperature of 120ºC. More specifically, a commercially-available mechanical relay (AgSnIn contacts) was sealed into a metal can with one of these materials, and placed in a heating chamber to operate, at an operating frequency of 0.5 Hz, 40,000 break operations of an inductive DC 14V-1A, 14V-0.4A, 10V-1A, 5V-1A load currents, or a resistive DC 14V-1A load current. Contact resistance values were measured at every 50 operations. As a result, the relays sealed with the acryl-based non-silicone-type polymeric cured material showed no deterioration in contact resistances, irrespective of the load conditions. On the other hand, the relays sealed with the silicone-containing polymeric cured materials showed more significant deteriorations and fluctuations of the contact resistance characteristics, and certain influences of load conditions on their behaviors were recognized.

Influences of vapors evaporated from a newlydeveloped acryl-based polymeric material (containing no silicone components) and conventional silicone-containing polymeric materials were evaluated with respect to their effects on contact resistance characteristics of relay contacts at an ambient temperature of 120ºC. More specifically, a commerciallyavailable mechanical relay (AgSnIn contacts) was sealed into a can with one of the two materials, and placed in a heating chamber to operate, at an operating frequency of 0.5 Hz, 40,000 break operations of an inductive DC14V-0.4A load current, an inductive DC5V-1A load current, or a resistive DC14V-1A load current. Contact resistance values were measured at every 50 operations, and compared with the results obtained in the similar operation tests conducted at an operating frequency of 1 Hz. As a result, the relays sealed with the acryl-based non-silicone-type polymeric material showed no deterioration in contact resistances, irrespective of the load conditions or operating frequencies. On the other hand, the relays sealed with the silicone-containing material showed more significant deteriorations and fluctuations of the contact resistance characteristics in the 0.5 Hz operations as compared with the cases of the 1 Hz operations.

No abstract