Polyethylene thermoelastic

Opschoor, A., and W. Prins Thermoelasticity and conformational behaviour of polyethylene and ethylene-propylene copolymers. J. Polymer Sci., Pt. C16, 1095 (1967). 

In our own recent low temperature studies45 of ultra high drawn polyethylene, a change in the background level of tan 6 in tensile tests when the environmental gas is changed, is attributed to thermoelastic effects resulting from the different heat transfer characteristics of the gases used. 

As far as the thermoelasticity performance of a polymer network k concerned, it is generally true that the hi er the concentration of crosslinks or the lower the dimensions of loopholes in the network, the more significant are the changes in the polymer I operties. The elasticity of a polymer is also enhanced by i iyskally entangled chains, whose number increases with the number of crosslinks, the character of the crosslinks being interrdated with the character of the physical aitan ements [27]. This may be illustrated by experiments with two crosslinked samples prepared from low density polyethylene. The first sample was crosslinked via the silane pathway, the second by... 

Fig. 1.15. Thermoelastic results on (amorphous) polyethylene networks and their interpretation in terms of the preferred, all-trani conformation of the chain [3, 6],...

McCrum [213, 214] recently suggested that the above approach is subject to large errors and based on an irrational premiss. He proposed a new method of thermoviscoelasticity . Smith and Mark [215] have demonstrated McCrum s analysis to be flawed and have shown that the classical thermoelasticity approach is soundly based on theory. Indeed, there is excellent agreement between thermoelastic and viscometric results for poly(l-pentene) [206, 211], polyethylene [151, 154, 155, 211, 216], poly(dimethyl siloxane) [205, 211, 217], poly(ethylene oxide) [211, 218], poly (isobutylene) [207, 211, 216, 219] and poly(H-butyl methacrylate) [220, 221] (Table 6). 

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