Polymers, motion in crystalline

Investigations of Motion in Crystalline Polymers and Related Substances... 

In crystalline polymers, the principal relaxation process is associated with melting. In polyethylene, a (1-. and 7-transit ions have been identified and, particularly in higb-tlensity polyethylene, the a-transition has been sub-divided into a and a. In ethylene-based polymers, the y-transitions at —120°C is generally associated with the amorphous phase, in particular, with crankshaft motion of methylene sequences. " However, based upon studies of solution grown lamellae, it has also been suggested that this may llien be associated with... 

Vega AJ, English AD (1980) Multiple-pulse nuclear magnetic resonance of solid polymers. Polymer motion in crystalline and amorphous poly(tetrafluoroethylene). Macromolecules, 13 1635... 

In the amorphous state, the distribution of polymer chains in the matrix is completely random, with none of the strictures imposed by the ordering encoimtered in the crystallites of partially crystalline polymers. This allows the onset of molecular motion in amorphous polymers to take place at temperatures below the melting point of such crystallites. Consequently, as the molecular motion in an amorphous polymer increases, the sample passes from a glass through a rubberhke state imtil finally it becomes molten. These transitions lead to changes in the physical properties and material application of a polymer, and it is important to examine physical changes wrought in an amorphous polymer as a result of variations in the molecular motion. 

Boyd RH (1985) Relaxation Processes in Crystalline Polymers Experimental Behavior Molecular Interpretation—A Review. Polymer 26 323-347 and 1123-1133. Wunderlich, B (1997) The Basis of Thermal Analysis. In Turi E ed. Thermal Characterization of Polymeric Materials 2" edn. Academic Press, New York, pp 387-389. Wunderlich B (1962) Motion in Polyethylene. III. The Amorphous Polymer. J Chem Phys 37 2429-2432. 

Glass transition Change of state of an amorphous or semi-crystalline polymer from a rubbery (or viscous) state to a glassy state. The glass transition is not a thermodynamic first- or second-order phase transition. It is a relaxation phenomenon which is characterized by a general enhancement of molecular motion in the polymer at the glass transition temperature. 

Because of their large molecular size, complex bonding patterns, the presence of side chains, and other characteristics, polymers exhibit a number of phenomena in the solid state that are much less common in crystalline solids. In the study of bulk polymers, the time, temperature, and other variable-related characteristics have come to be classed as either relaxations or transitions. As a general definition, a relaxation can be considered a time-dependent motion in a polymer system in which the molecules return to an equUibrium from which they have been displaced by the action of some external force. For example, if a polymer sample is compressed under some external load that forces the molecules to rearrange to attain a new equUibrium state and the force is then removed, the material will, with time, relax or return to its original state (before compression). 

The WLF formula shows that the ionic conductivity of the polymer electrolyte is shown in the temperature range higher than Tg. Ionic conductivity decreases rapidly if its temperature goes below that of Tg. The EO unit is recognized as the most excellent structure from the ionic dissociation viewpoint. The ion is transported coupled with the oxyethylene chain motion in amorphous polymer domain. However, oxyethylene structure easily becomes crystalline. Therefore, in order to accelerate the quick molecular motion of the polymer chain and quick ion diffusion, it is important to lower the crystallization of polymer matrixes. The methods for inhibiting the crystallization of the polymer are, for example, to introduce the polyethylene oxide chain into the low Tg polymer such as polysiloxane and phosp-hazene, or to introduce the asymmetric units such as ethylene oxide/propylene oxide (EO/PO) into polymer main chain. 

If, in their use conditions, polymers are subjected to a residual molecular mobility (Ji motions in glassy polymers, a motions in the rubbery amorphous phase of semi-crystalline polymers), they will undergo a molecular reorganization towards the thermodynamic equilibrium, characterized by ... 

Recall that the diffusion coefficient in a glass of water equals 10 " - 10 cmVs, in melted polymer - 10 in a solid amorphous polymer - 10 , and in crystalline polymer - lO -lO" cmVs. Thus the molecule s motion and speed at transition from liquid low molecular compoimd to solid crystalline polymer may vary by 20 orders of magnitude or higher. Hence, a transition from kinetic area (when the reaction rate is defined by reactivities of the substances) to diffusion area (when the situation is completely defined by reagent delivery to the interaction site and the Frank-Rabinovich cage effect) may occur. 

In crystalline polymer systems the tough response, besides cavitation and crazing, is crystallographic in natme. Crystallographic slips ai-e the main plastic deformation mechanisms that require generation and motion of crystallographic dislocations. The concepts of generation of monolithic and half-loop dislocations plausibly explain the observed yield stress dependences on crystal thickness, temperatm-e and strain rate. 

---