Flexibility, polymer

The high intermolecular attraction leads to polymers of high melting point. However, above the melting point the melt viscosity is low because of the polymer flexibility at such high temperatures, which are usually more than 200°C above the Tg, and the relatively low molecular weight. 

To any one concerned with the production of plasticized resins, compatibility has long meant the ability of two or more materials to mix with each other to form a homogeneous composition of useful desired plastic properties [44,45]. A plasticizer, therefore, can be defined as a material that will soften and make inherently rigid and even brittle polymers flexible. Plasticizers are also sometimes... 

Polymer Flexibility as a Decisive Parameter of the Thermodynamic and Kinetic Features of Orientation Processes... 

Figure B8.2.1 shows the fluorescence spectra of DIPHANT in a polybutadiene matrix. The h/lu ratios turned out to be significantly lower than in solution, which means that the internal rotation of the probe is restricted in such a relatively rigid polymer matrix. The fluorescence intensity of the monomer is approximately constant at temperatures ranging from —100 to —20 °C, which indicates that the probe motions are hindered, and then decreases with a concomitant increase in the excimer fluorescence. The onset of probe mobility, detected by the start of the decrease in the monomer intensity and lifetime occurs at about —20 °C, i.e. well above the low-frequency static reference temperature Tg (glass transition temperature) of the polybutadiene sample, which is —91 °C (measured at 1 Hz). This temperature shift shows the strong dependence of the apparent polymer flexibility on the characteristic frequency of the experimental technique. This frequency is the reciprocal of the monomer excited-state...

While most CA s of disaccharides have depended only on intrinsic characteristics of the molecule, experimental results depend strongly on the environment. By experiment, Kamide and Saito ( ) have shown that the degree of flexibility of cellulose and its derivatives is strongly dependent on the dielectric constant of the solvent as well as the exact type and degree of substitution. Since a substantial portion of the polymer flexibility depends on the extent of variability of the torsion angles at the intermonomer linkage, the dependence of polymer flexibility on type of solvent and substitution means that the disaccharide flexibility also should depend on those factors. Non-polar solvents allowed the molecules to have greater flexibility than did polar solvents (35). 

In any case, the Arrhenius equation is not particularly useful at temperatures above Tg + 100 K. The overall temperature-dependence of polymer flexibility at temperatures of Tt to T% + 100 K can be expressed by the empirical Williams, Landel, and Ferry (WLF) equation... 

Wang and DuPre [94] found that for the PHIC-chloroform system the S values were much larger than predicted by modified Lee s theory with q = 21-37 nm (cf. Table 1). Although DePie and Yang [46] fitted their data to the theory incorporating the polymer flexibility effect, the value of q = 89 nm used is too large when compared with that estimated from the intrinsic viscosity data [98]. 

As sparse as the dataset describing mainchain nematic LCP blends with conventional polymers is, it is rich compared to the almost non-existent data on the blending of other types of LCPs-side chain polymers, flexible spacer polymers, smectics, etc. 

Comfort cushioning is the largest single application of cellular polymers flexible foams are the principal contributors to this field. However, the rapid growth rate of structural, packaging, and insulation applications has brought their volume over that of flexible loams during the past Tew years. Table 5 shows U.S, consumption of foamed plastics by resin and market,... 

Figure 2 Properties in polyphosphazenes are determined hy (1) the backbone bonds that control the inherent flexibility of the polymer via their influence on bond torsional freedom, and also provide photo-and thermo-oxidative stahihty (2) the side groups control polymer solubility, reactivity, thermal stability, crystallinity, cross-linking, and (indirectly) polymer flexibility (3) free volume between the side groups affects polymer motion, solvent penetration, membrane behavior, and density (4) functional groups (usually introduced hy secondary reactions) affect soluhihty, biological behavior, proton conduction, cross-hnking, and many other properties...

The main source of polymer flexibility is the variation of torsion angles [see Fig. 2.1(a)]. In order to describe these variations, consider a plane defined by three neighbouring carbon atoms C, 2, C, i, and C,. The bond... 

A third feature for solubility is molecular architecture, especially in the case of large compounds such as polymers. The polymer should exhibit large free volume with a high degree of flexibility. A good indication of polymer flexibility and high free volume is a low glass transition temperature. 

Both conformational preferences and kinetics are different for different monomers (depending on ring size, substitution, nucleophilicity of the heteroatom in monomer and polymer, flexibility of the chain) and even for a given monomer may change with changing solvent, temperature or counterion. 

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