Crosslinks thermoelasticity

Other studies of interest include the modification of polysulphone membranes using crosslinking agents, thermoelastic properties of network polymers, and the effects of coating thickness on initiator activity for oligourethane acrylates and triethylene glycol dimethacrylate. ... 

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... 

Thermoelastics are chemically or physically wide-meshed crosslinked plastics that become elastic above the softening temperature (glass transition temperature) or fusing temperature, but do not flow viscously up to the decomposition temperature, making them nonprocessable as thermoplastics. Below the softening temperature, their characteristics are similar to thermoplastics. 

The idea that the critical behaviour of LCEs may be influenced by varying the geometry and density of the crosslinkers was introduced in an early theoretical work [23]. Indications that an increased crosslinking density leads to a more gradual (more supercritical-like) thermoelastic response and birefringence temperature dependence may be found in various publications [7, 18]. Recently, the first systematic and dedicated experimental investigation, by means of H-NMR and high-resolution calorimetry [4,5], demonstrated that the increase in the crosslinkers... 

Thermoelastic measurements on such samples reveal a spontaneous elongation along n at the transition to the smectic phase, indicating a prolate polymer backbone conformation in the smectic elastomer [137]. On another hand, SANS results for end-on side-chain polymers in the smectic phase indicate an oblate chain conformation, with the backbone preferentially confined in the plane of the layers (Sect. 2.2). Thus, the chain distribution and macroscopic shape of the smectic elastomer change their sign if crosslinking is made under uniaxial mechanical stress in the isotropic and/or nematic phase. This result is remarkable and indicates that the oblate chain conformation of a smectic end-on polymer can be easily turned into prolate by a low uniaxial extension during solvent evaporation. 

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