Gauche conformations, polymer melts

Figure 4 Cartoon for hidden liquid-liquid spinodal in a polymer melt, calculated for a Flory Rotational Isomeric State chain with a simple coupling between density and conformational order A is the trans-gauche energy gap and a dimensionless density. Shown is the path of an isochoric quence into the unstable regime. r, is the spinodal temperature, T the melting temperature, T the liquid-liquid critical point, and Tp the temperature at which the harrier between dense liquid and crystal is of order ksT ...

The IR evidence of PEO in the crystalline form, the melt, and in benzene solutions indicated that (1) the conformation of the repeating unit in crystalline PEO is in the TGT form as previously suggested [19, 25, 26], (2) in the melt or in benzene solution most of the ethylene groups in PEO remain in the gauche conformation, and the disorder of the polymer chain occurs mainly at the C-O bonds, (3) the conformations of the repeating unit of oligomeric PEO in benzene become more disordered in the dissociated state than in the associated form, and (4) the random conformations of... 

Unlike other synthetic polymers, PVDF has a wealth of polymorphs at least four chain conformations are known and a fifth has been suggested (119). The four known distinct forms or phases are alpha (II), beta (I), gamma (III), and delta (IV). The most common a-phase is the trans-gauche (tgtg ) chain conformation placing hydrogen and fluorine atoms alternately on each side of the chain (120,121). It forms during polymerization and crystallizes from the melt at all temperatures (122,123). The other forms have also been well characterized (124—128). The density of the a polymorph crystals is 1.92 g/cm and that of the P polymorph crystals 1.97 g/cm (129) the density of amorphous PVDF is 1.68 g/cm (130). 

Poly(ethylene 2,6-naphthalate) (PEN) film containing alpha, beta and amorphous phases were prepared, and the amorphous contribution digitally subtracted to yield the characteristic spectra of the amorphous, alpha, and beta phases. In other words, the amorphous spectrum is determined by melting the polymer, so after subtraction, one knows the spectrum of all of them. The alpha crystal form adopts an all-rran conformation, while the beta crystal form adopts a conformation with appreciable gauche character. Conformational changes in PEN occur due to the rotation of the naphthalene ring as well as rotation of the ethylene glycol units. The normalised absorbances of the bands at 824 and 814 cm were correlated to polymer density, and can be used to represent the amorphous and alpha crystalline phases, respectively (56). 

Syndiotactic polystyrene, s-PS, is a highly stereoregular, semicrystalline vinyl polymer that normally melts at 270 °C [45,46], S-PS shows a large number of crystalline polymorphs [47-50] obtained by melt crystallization and solvent-exposure techniques. However, s-PS assumes only two distinct crystalline conformations [all trans, planar zigzag (... tttttttt...) and 2 -helical (... ttggttgg. ..) t= trans and g = gauche], which are characterized by fiber repeats of... 

Potential impact of rotator phase on crystallization. Molecular dynamics simulations have been carried out to study the conformational defects in the orientationally ordered structures of short-chain molecules and polymer chains. The simulation showed the creation of orientationally ordered structures from a random coil configuration by cooling from the melt. The longer chains exhibit folding with double gauche defects with the same sign ( tg( + )g( + )t. . . ) predominantly located at the chain ends and the kink... 

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