Polymer chain mobility

Asloun, El. M., Nardin, M. and Schultz, J. (1989). Stress transfer in single-fiber composites Effect of adhesion, elastic modulus of fiber and matrix and polymer chain mobility. J. Mater. Sei. 24, 1835-1844. 

The melting point is the temperature range in which total or whole polymer chain mobility occurs. The melting point (T ) is called a first-order transition temperature, and Tg is sometimes referred to as a second-order transition. The values for T are usually 33%-100% greater than for Tg. Symmetrical polymers like HDPE exhibit the greatest difference between T and Tg. The Tg values are low for elastomers and flexible polymers such as PE... 

The temperature at which local segmental mobility occurs is called the Eg and that at which wholesale polymer chain mobility occurs is called the T -... 

In composite systems, 2H NMR is particularly suited to investigate interfacial properties. Indeed, isolated nuclei are observed, which potentially allows spatially selective information to be obtained. It has been used to investigate polymer chain mobility at the polymer-filler interface, mainly in filled silicon (in particular PDMS) networks. The chain mobility differs considerably at the polymer-filler interface, and this may be interpreted in terms of an adsorbed polymer layer at the filler surface. T1 relaxation measurements allowed to determine the fraction of chain units involved in the adsorption layer, or equivalently, the thickness of the layer [75, 76, 77]. The molecular mobility and the thickness of the adsorption layer are very sensitive to the type of filler surface [78]. 

The epoxy resin data and the post-cure data, taken together, show that the dipolar relaxation is associated with the temperature dependence of the polymer chain mobility in the vicinity of the glass transition. The WLF analysis of the dipolar relaxation during cure has not been carried out. In order to complete the analysis, correlated measurements of Tg, extent of cure, and dielectric properties must be made as functions of cure time and temperature. In the absence of such definitive studies, various indirect methods have been employed to analyze dielectric relaxations in curing systems, as described below. 

Monomer II is also a polymerizable IL composed of quatemized imidazoliimi salt, as shown in Figure 29.1. This monomer is liquid at room temperature and shows a Tg only at —70°C. Its high ionic conductivity of about 10 S cm at room temperature reflects a low Tg. Although the ionic conductivity of this monomer decreased after polymerization as in the case of monomer I, it was considerably improved by the addition of a small amount of LiTFSI. Figure 29.3 shows the effect of LiTFSI concentration on the ionic conductivity and lithium transference number ( Li ) for polymer II. The bulk ionic conductivity of polymer II was 10 S cm at 50°C. When LiTFSI was added to polymer 11, the ionic conductivity increased up to 10 S cm After that, the ionic conductivity of polymer II decreased gradually with the increasing LiTFSI concentration. On the other hand, when the LiTFSI concentration was 100 mol%, the of this system exceeded 0.5. Because of the fixed imidazolium cations on the polymer chain, mobile anion species exist more than cation species in the polymer matrix at this concentration. Since the TFSI anions form the IL domain with the imidazolium cation, the anion can supply a successive ion conduction path for the lithium caiton. Such behavior is not observed in monomeric IL systems, and is understood to be due to the concentrated charge domains created by the polymerization. 

In addition, we have probed hydrolyzed Estane sample with the NMR Mobile Universal Surface Explorer (NMR MOUSE) (10). This technique is a quick non-invasive technique to determine the effect that polymer degradation has on its physical properties. Polymer chain mobility can be detected by proton spin-spin relaxation time measurements of hydrolyzed Estane using the NMR MOUSE. The spin-spin relaxation time decay curve shows increased chain mobility upon hydrolysis (Figure 11). The decay curve is fitted with a biexponential decay function to give two T2 values. The T22 associated with the more mobile polymer chains shows an inverse relationship to the molecular weight decrease as would be expected. This technique shows promise as an in situ probe of hydrolysis in high explosives in a non-destructive manner. 

The surface dynamic changes, irrespective of starting points, occur in the direction to minimize the interfacial tension between polymer and the contacting medium. The overall change in the surface configuration can be viewed as the product of two major parameters, i.e., (1) polymer chain mobility and (2) driving force ... 

Diffusional flux = T(polymer chain mobility) x G(concentration gradient)... 

Consequently, any factor that changes the polymer chain mobility and any factor that changes interfacial tension cause the change in the rate of surface configuration change. 

Weakly Interactive liquids. Such solvents do not provide sufficient free volume for polymer chain mobility characteristic of the rubbery state ( S). The PET/methanol system Illustrates this amorphous PET imbibed with methanol at s 25 C remains noncrystalline Indefinitely (20), indicating severely restricted chain mobility even in the swollen state. For such systems, the kinetic restrictions to chain rearrangement prevent the rapid achievement of equilibrium in surface layers ( ). As a result, the solvent surface concentration Increases slowly during the sorption process. Several authors (12, 17,28-30) have suggested specific relationships governing the time dependence of the surface concentration in such cases we have employed a simple exponential Increase, viz. ... 

Decomposition of a -labeled mixed anhydride (DF 0.13, 1.0 mmol/g) in a popcorn polystyrene produced polymer-bound carbonate and benzoate esters (Scheme 10) (US). At 25 C for one year or at 100 C for 10 h the dry resin gave 20% or 25% intermolecular decomposition. The resin in dioxane at 90 <>C for 10 h or at 37 °C for 15 h with added triefliylamine gave S4% or 82% intermolecular decomposition. The swelling solvent provided the polymer chain mobility needed for reaction between two polymer-bound functional groups. 

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