Flexibility of the Polymer Chains

The existence of the mesophase layer has been proved by infra-red spectroscopy, ESP, NMR, electron microscopy and other experimental methods. Moreover, it has been also proved that the thickness of this layer depends on the polymer cohesion energy, free surface energy of the solid, and on the flexibility of the polymer chains. 

As was expected, the substitution of PPO with rigid and bulky side groups decreases the flexibility of the polymer chain and the glass transition temperatures of modified polymers increases. This... 

In a similar way, Mizota et al. grafted polymer chains functionalized with sulfonic sites over a polystyrene-type polymer. As observed above, the flexibility of the polymer chains allowed better accessibility of the catalytic sites and this solid acid catalyst was ten times more active than the conventionally used cross-linked resin in the hydrolysis of sucrose (Scheme 2) [27]. 

The diffusion of larger organic vapor molecules is related to absorption. The rate of diffusion is dependent on the size and shape of the diffusate molecules, their interaction with the polymer molecules, and the rise shape, and stiffness of the polymer chains. The rate of diffusion is related directly to the flexibility of the polymer chain and inversely to the size of the diffusate molecule. 

The lack of flexibility of the polymer chain has to be improved by introducing linkage groups into the dianhydride component. Accordingly, continuous and flexible films of perfluorinated polyimides are expected to be obtained by combining diamines, which have high reactivities, with dianhydrides, which have flexible molecular structures. 

We believe the difficulty is that the free-volume theory as applied to the glass-transition does not take account of the essential role of intra- and intermolecular interaction in the system and the flexibility of the polymer chains, all of which factors play an important role in the glass-transition phenomena. 

In the preceeding section we discussed physisorbed polymers. Now we concentrate on chemisorbed polymer layers (review Ref. [424], see also Section 6.7). Chemisorbed polymers on solid surfaces have the advantage of forming thick flexible layers up to several 100 nm thickness. Due to the flexibility of the polymer chains the layer is relativley homogeneous. Additionally, the large variety of the monomers suitable for surface polymerization leads to a large variety in the surface properties. Also, the mechanical flexibility can be manipulated by the polymer chain density. A high density leads to polymer brushes. 

The rate of this reaction strongly depends on the pH (Fig. 9.3), i.e., the protonation state of the polymer. With increasing pH, the rate of reaction slows down considerably, an indication that the flexibility of the polymer chain is of importance for this reaction to occur efficiently. Whether this implies that H-abstrac-tion mainly occurs from distant sites and not from a neighboring subunit [as shown in reaction (4)], cannot be decided yet on the basis of the existing data. 

Here three constants appear Go is the equilibrium modulus of elasticity 0p is the characteristic relaxation time, and AG is the relaxation part of elastic modulus. There are six measured quantities (components of the dynamic modulus for three frequencies) for any curing time. It is essential that the relaxation characteristics are related to actual physical mechanisms the Go value reflects the existence of a three-dimensional network of permanent (chemical) bonds 0p and AG are related to the relaxation process due to the segmental flexibility of the polymer chains. According to the model, in-termolecular interactions are modelled by assuming the existence of a network of temporary bonds, which are sometimes interpreted as physical (or geometrical) long-chain entanglements. 

Figure 2 shows the degree of hydrolysis of poly(MAOT-co-AA) (Sample no. 10 in Table 3), poly(AOT-co-AA) (No. 15), and poly(MAOA-co-AA) (No. 12) at 60 °C in a 0.1 M phosphate buffer solution (pH 7.8) as a function of time. Acryloyloxyethyltype copolymer (poly(AOT-co- AA)) was hydrolyzed rather easily, but no significant difference between the kinds of leaving group was observed. The flexibility of the polymer chain is supposed to be an important factor for the hydrolysis of the polymer side chain. 

The molar volume in these equations is difficult to assign. This was found to be a problem in the case of a polar liquid. Recently Roe (29) pointed out that, in the case of polymeric liquids, the thickness of the transition layer depends not only on the size of the repeat unit but also on the degree of correlation between successive structural units, or, in other words, on the flexibility of the polymer chain. It is, therefore, not appropriate to use the cube root of the molar volume as a measure of the thickness of the monomolecular layer at the vapor-liquid interface. 

If the monomers are uniformly distributed within the polymer chain, the ratio of monomers will define the flexibility of the polymer chain.10 Because many properties depend on this chain mobility, polymer composition is carefully controlled. In addition to... 

An easy recovery of a catalyst from a mixture of reagents/products as well as its simple handling and recycling are important problems in chemical synthesis. Consequently, new recoverable catalysts attract increasing attention and the use of polymeric supports became a common practice. Polystyrene [1] is one of the most popular polymer supports due to its availability, facile functionalization and chemical inertness. However, such organic polymers usually show a solvent swelling dependent performance, which impacts the catalytic activity of the supported species. Polysiloxanes, due to unusually high flexibility of the polymer chain and low barrier... 

In solution, the flexibility of the polymer chain allows the polymer to collapse into a compact, randomly coiled structure rather than to retain an extended form. A transition between these two forms can be observed depending on solvent quality and temperature and is best known as the rod-to-coil transition of biomacromolecules such as DNA. 

Soper et al. have investigated the copolymerization of St with DVB [21] the intrinsic viscosity [ii] of the resulting polymer was measured in order to explore the occurrence of intramolecular cyclization leading to the formation of loop structure and thus, resulting in the reduced [r ] of the polymer. As a matter of course, this intramolecular cyclization is influenced by the flexibility of the polymer chain, the content of pendant double bonds, and the primary chain length. 

The optimisation of the polymer structure proved to be rather complicated. On the one hand, the polymers should be rather rigid to preserve the structure of the cavity after the template is split off. On the other hand, a certain flexibility of the polymer chain is necessary to facilitate the attainment of a fast equilibrium between... 

Nature of the polymer the greater the flexibility of the polymer chains, the greater will be the diffusivity. An increase in the cohesive energy of the polymer reduces diffusivity. 

As can be seen from Table 1, the parameter Vj increases with increasing molecular weight of PDMS-OH because the flexibility of the polymer chains increase in the same direction. Furthermore, the ratio CT/LE shows higher values with increasing molecular weight of PDMS-OH because of an... 

Comparing each structure of the first series 7a-d to the structurally similar polymers of the second series 8a-d, the second series possesses Tg which are 11-16 °C higher. This indicates that by replacing two methyl groups with two trifluoromethyl groups in the dianhydride moiety, the flexibility of the polymer chain decreases. All synthesized F-PEIs exhibit excellent temperature stability In air they show a 5 wt% loss between 530 °C and 540 °C, but for 7d, the Ts% is at 495 °C. 

If there is restricted rotation about the inter-unit bond in the polymer chain (because of the presence, for example, of large substituent groups), Am will be increased. This parameter is, in fact, an inverse measure of the molecular flexibility of the polymer chain (as is also the parameter b of the Kirkwood-Riseman treatment), and so, of the tightness of the random coil and its tendency to immobilize the entrained solvent. 

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