Polymer chain packing

Mesomorphic forms characterized by conformationally ordered polymer chains packed in lattices with different kinds of lateral disorder have been described for various isotactic and syndiotactic polymers. For instance, for iPP,706 sPP,201 sPS,202 syndiotactic poly(p-methylstyrene) (sPPMS),203 and syndiotactic poly(m -methylstyrene),204 mesomorphic forms have been found. In all of these cases the X-ray fiber diffraction patterns show diffraction confined in well-defined layer lines, indicating order in the conformation of the chains, but broad reflections and diffuse haloes on the equator and on the other layer lines, indicating the presence of disorder in the arrangement of the chain axes as well as the absence of long-range lateral correlations between the chains. 

Scheme 1 Representation of polymer chain packing in PEI controlled by the formation of and subsequent coalescence from its y-CD-inclusion compound...

The presence of crystalline materials has a strong influence on their properties, e.g. polymer chains pack more tightly together, hence have a higher density, as shown by LDPE (60-65% crystalline), HDPE (90-95% crystalline), with densities of, say, 0.915 and 0.965 respectively. 

In the lamellar crystals of semicrystalline materials and the extended chain structure of oriented polymers, chain packing is usually much more efficient than in the amorphous, isotropic state. The efficiency of chain packing in the crystalline phase reduces the free volume available for transport to such an extent that, as a first approximation, the crystalline phase may be regarded as impermeable relative to the amorphous phase. 

It has been reported recently that flux and even selectivity of PMP and PTMSP can be enhanced by the addition of nanoparticles (285, 286]. Merkel et al. [285] added fumed sihca to PMP and observed a simultaneous increase of butane flux and butane/methane selectivity. This unusual behavior was explained by fumed-silica-induced disruption of polymer chain packing and an accompanying increase in the size of free volume elements through which molecular transport occurs. Gomes et al. [286] incorporated nanosized sihca particles by a sol-gel technique into PTMSP and found also for this polymer a simultaneous increase in flux and selectivity. It has to be studied, if physical aging of the polyacetylenes is reduced by the addition of nanoparticles. 

The sheet conductivities of the PPy-PEO composite nanofiber mats were in the order of 10" S/cm calculated from the four-probe measurement data. Conductivities of electrospun nanofibers measured by using the four-probe method were about 10" S/cm. PPy was coated on PS nanofiber mats, and the conductivities of the PS-Cl-PPy and PS-TS-PPy fiber mats were found to be 2 x 10" S/ cm and 5 x 10 S/cm, respectively. It was demonstrated that the conductivity of the porous fiber mat could be influenced by the amount (PPy/PS ratio), doping, and crystallinity (polymer chain packing) of PPy in the fibers, the void volume, and the connectivity between fibers in the mat. When the PS template of the PS-TS-PPy fiber mat was removed by THF treatment and the electrical conductivity of the remaining material (TS-PPy) was measured, the conductivity increased to 0.13 S/cm by using the four-probe Van der Pauw method. ... 

According to Equation (27.8), an increase in polymer free volume is expected to enhance penetrant diffusion. It could be described that the increased free volume results from the disruption of nanofillers in polymer-chain packing. Thus, gas diffusion through rubbery polymer is enhanced and subsequently... 

For hybrid membranes, the presence of nanofillers can influence the polymer chain packing results in a larger free volume in the hybrid matrix compared with the neat... 

The effect of the heterocyclic moiety and the catenation angle on the poly(ether amide)s was also investigated [47]. It was observed that with the decrease in the catenation angle, the solubility of the polymers increased due to the inhibition in polymer chain packing. All these PAs (Figure 4.7) showed good thermal stability (Tdjo%=409-475 °C) under air. Differential... 

If the polymer chain packing is not perfect, interchain disorder will reduce the interchain transfer rate and hence decrease the conductivity. A more realistic model describes heterogeneous polymers. Polymer chains are packed into a bundle and are well ordered inside the bundle. The interchain localization length in the perpendicular direction is Na and the in-chain localization length is M, where / is the localization length in a strictly one-dimensional chain. The state inside these bundles is metallic if localization lengths are high in comparison with lattice constants, Lp > c and > a. The electrical behavior of particular samples is controlled by the dimensions of the bundles. 

Pouget et al. [55] have compared the structural characteristics of POT-CSA with PANI-CSA as obtained from the X-ray powder patterns. They emphasize that polymer chain packing, disorder and interchain separation have a key influence on the charge conduction process. The degradation of metallic properties from PANI-CSA to POT-CSA can be ascribed to the enhancement of disorder and to a large increase in the interlayer separation due to the presence of bulky -CH3 groups. 

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