If the system is amorphous polymer, then no with the anchor points of the crystal structure and the only way to ensure the stability of the temporary is through chain entanglements (physical entanglements and chemical cross-linking does not), plus the ability of the state entrecruzamiento.En vitreous, the movements of long-chain segments are frozen, the movements of these segments depends on an activation temperature that leads to a state rubberized polymer, elastic rotation about the carbon bonds and the movement of the chains are no longer strong enough to accommodate disabilities and to acquire the conformation requires less energy, then chains "unravel" forming random strings without a warrant and therefore more entropy.
If a polymer sample is stretched for a short time in the elastic range, to eliminate the burden, the sample recovered its original form, but if the charge remains for a long enough period, the chains are rearranged and the original form is not recovers the result is an irreversible deformation, also called relaxation process (in this case: English creep or creep).
a polymer to make this the thermal effect of memory, it is necessary to set anchors the strings to avoid these relaxation processes that modify the system.The inelastically amorphous polymers do not have a crystallization temperature (Tm) and the semi-crystalline and have only a glass transition temperature (Tg). This strongly influences the behavior of polymer systems with memory.
is necessary to take into account that a system of self crystalline copolymers alone can be treated with the copolymer loses its crystallinity and crossovers is practically amorphous.
An amorphous polymer crosslinking depends on the level or degree of polymerization, to present this effect. In the case of poly (norbornene) is a linear polymer, amorphous, containing 70 to 80% of trans bonds in commercial products, molecular weight of about 3x106 g mol-1 and Tg approximately 35 to 45 ° C. Because it reaches an unusually high degree of polymerization can be trusted in the entanglements of the chains as anchors to achieve the thermal effect of memory. Therefore this polymer depends solely on physical anchor points. When heated to Tg, the material changes abruptly from a rigid state to a state rubberized (softens). To achieve the effect, the form must be changed quickly to avoid the rearrangement of polymer chain segments and immediately cool the material with high speed also below Tg. By heating the material back to Tg is observed recovery of the original shape.
Maria Linares 19881179 EES
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