Flexibility of a polymer chain

The dissolution of polymer is determined by chain flexibility. The mechanism of dissolution consists of separating chains from each other and their transfer into solution. If a chain is flexible, its segments can be separated without a large expenditure of energy. Thus functional groups in polymer chain may interact with solvent molecules. 

Thermal movement facilitates swelling of polymers with flexible chains. The flexible chain separated from an adjacent chain penetrates easily into solvent and the diffusion occurs at the expense of sequential transition of links. 

The spontaneous dissolution is accompanied by decrease in free energy (AG 0) and that is possible at some defined values of AH and AS. At the dissolution of high-elasticity polymers AH 0, AS 0 then AG 0. Therefore high-elasticity polymers are dissolved in solvents completely. 

Glassy polymers with a dense molecular sfructure swell in solvents with the heat absorption AH 0. The value of AS is very small. Therefore AG 0 and spontaneous dissolution is not observed and the limited swelling occurs. To a greater degree this concerns crystalline polymers which are dissolved if AH 0 and AH TAS.  

When molecular mass of elastic polymers is increased, AH does not change but AS decreases. The AG becomes less negative. In glassy polymers, the increase in molecular mass 

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The minimum polymer chain length or critical molecular weight, M for the formation of stable entanglements depends upon the flexibility of a polymer chain which is affected by the polarity and shape of the polymer. Relatively flexible polymer chains, such as polystyrene, have a... 

These factors were mentioned soon after the first experimental works on liquid crystalline state of polymers were published. For example, Frenkel considered the effect of these factors by studying the change in the statistical flexibility parameter/ introduced by Flory in his analysis of flexible chain polymers Frenkel proposed the following equation to describe the effect of the type of the solvent on the flexibility of a polymer chain ... 

As we know, the flexibility of a polymer chain is not very noticeable at smaller scales, but it starts showing up as the scale increases. This means... 

The chemical structure of a polymer chain determines its statistical properties, such as its average dimensions in space and its flexibility. These parameters, in turn, affect various properties of a network consisting of these chains. A detailed understanding of the single chain is therefore important in this regard. 

Chain flexibility also effects the ability of a polymer to crystallize. Excessive flexibility in a polymer chain as in polysiloxanes and natural rubber leads to an inability of the chains to pack. The chain conformations required for packing cannot be maintained because of the high flexibility of the chains. The flexibility in the cases of the polysiloxanes and natural rubber is due to the bulky Si—O and rxv-olelin groups, respectively. Such polymers remain as almost completely amorphous materials, which, however, show the important property of elastic behavior. 

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]. 

With increasing polymer concentration, we may expect that the polymer global motion changes from the fuzzy cylinder model mechanism to the repta-tion model mechanism. The onset of the crossover should depend on the degree in which the lateral motion of a polymer chain is suppressed by entanglement with its surrounding chains, but it is difficult to estimate this degree. There are some disputes over it in the case of flexible polymers [20]. 

The conformational entropies of copolymer chains are calculated through utilization of semiempirical potential energy functions and adoption of the RIS model of polymers. It is assumed that the glass transition temperature, Tg, is inversely related to the intramolecular, equilibrium flexibility of a copolymer chain as manifested by its conformational entropy. This approach is applied to the vinyl copolymers of vinyl chloride and vinylidene chloride with methyl acrylate, where the stereoregularity of each copolymer is explicitly considered, and correctly predicts the observed deviations from the Fox relation when they occur. It therefore appears that the sequence distribution - Tg effects observed in many copolymers may have an intramolecular origin in the form of specific molecular interactions between adjacent monomer units, which can be characterized by estimating the resultant conformational entropy. 

So far, it has been shown that the stability of a model membrane can be tremendously increased by polymerization. This increased stability however, is associated with the presence of a polymer chain in the membrane itself or on its surface, bringing about increased viscosity and thus reduced flexibility. How does the reduced membrane mobility affect one of the most vital properties of biomembranes, the phase transition ... 

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. 

Some examples of stiff-chain polymers able to form a liquid-crystalline phase in the solution are listed in Table l1. The ratio of the statistical segment length1 of a polymer chain, 1, to its width, d, (last column of Table 1) measures the degree of chain stiffness. For flexible macromolecules fid 1 stiff-chain macromolecules are those for which fid t> 1. 

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... 

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