Restricted chain mobility

Polymers with a high cross-link density do not melt. A small degree of cross-linking restricts chain mobility and increases the Tg values. Partly crystalline polymers may be flexible at temperatures above the Tg and below the T... 

The presence of two substituents on every alternate carbon atom restricts chain mobility, so polyalkyl methacrylates are less flexible than the corresponding polyalkyl acrylates. Also, the presence of an alpha alkyl group increases (compared with the corresponding polyalkyl acrylates) the stability of polyalkyl methacrylates to light and chemical degradation,... 

Control of this property is possible by controlling the structure of the polymer chain. Monomers with bulky side groups restrict chain mobility and thus raise the glass transition temperature. The composition of copolymers and the ratio of polymer blends often are determined by the desired glass transition temperature of the final product. 

Figure 11 (a) Schematic representation of an ion-cluster ( multiplet ) and the region of restricted chain mobility according to the EHM-model... 

The amount of bound rubber depends on carbon black loading (Figure 7.20). Experimental studies show that small additions of carbon black (below 40 phr) obey different relationship than larger additions. The cross-section of both relationships gives a critical coherent loading. This data also shows that bound rubber increases rapidly above 30 phr. Above 80 phr, the bound rubber content begins to level off. NMR studies show a very restricted chain mobility above 80 phr. ... 

In polymersomes with thicker membranes the limited mobility of high MW polymer chains is the reason for the better resistance to dissolution. Thus, while liposomes would normally be destroyed when exposed to SDS (sodium dodecyl sulfate) or other strong detergents, polymer vesicles would be more resistant to detergents since this process is obstructed by the restricted chain mobility. Combination of experimental data and theoretical modeling suggests that polymer vesicle dissolution is mediated by the diffusion of detergent molecules across the membrane [132],... 

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. ... 

Because is a function of macromolecular mobility, any changes to the macromolecular structure that increase or decrease this mobility will have similar effects on Tg. For example, increased cross-linking restricts chain mobility of larger macromolecular segments, while increased attractive forces between molecules (as measured by the solubility parameter, C7p) require more thermal energy to produce... 

The processes involved in the formation of a crystalline polymeric solid are complex and still open to some debate. Using the analogy of the short-chain hydrocarbon dodecane (Chapter 1), the crystallization process simplistically involves the creation of favourable interactions between neighbouring chains. However, such an approach does not recognize the unique features possessed by polymers restricted chain mobility and the elfects of entanglement and other long-range interactions. 

The effective molecular weight for influencing physical properties is thus highly affected hy the mohihty of these chain ends. This can be controlled by the use of bulky end groups that restrict chain mobility in the solid state, but do not significantly affect chain mobility in the melt. 

In the case of SBR, which cannot easily achieve bond formation, when 40 phr of easy processing channel (EPC) black is added the tack is reduced and then remains almost the same during mastication. The filler in this case further restricts chain mobility, reducing interfacial interactions and thus leading to lower tack. If an SBR can be synthesised with... 

It was claimed that the hard cyclic structure restricts chain mobility to become an effective tie-down point (thus avoiding the need for chemical cross-linking). When 65% of the formulation was the poly(tetramethylene ether)glycol, elastic fibres similar to the Spandex polyurethane fibres were obtained. 

In their paper Perry et al. proposed that the hard cyclic structure restricted chain mobility and became an effective tie-down point. From subsequent experience with the thermoplastic polyether-polyesters and the S—B—S materials it would seem reasonable to suppose that blocks of the polycarbonate of the cyclic glycol provided the basis of the hard segment rather than single cyclic glycol units randomly positioned along the polymer chain. 

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