Ttgg conformation

Since two resonance lines at 39.0 and 47.7 ppm that correspond to those observed in the ttgg form and a resonance line at 49.0 ppm that corresponds to that in the tttt form are recognized in the gel spectrum, a coexistence of these two forms in the gel might be supposed. In an attempt to determine the possibility of the coexistence of the two forms in the gel, we measured the IR spectrum that is sensitive to the molecular conformation. The number of normal vibrational modes depends sensitively on the molecular conformation based on the selection rule of the symmetry species. Kobayashi et al. confirmed the vibrational modes assignable to the ttgg conformation in the IR spectrum for the gel from a sPP/carbon disulfide system [117]. However, since we used o-dichlorobenzene as solvent, we examined whether the gel structure depends on the solvent. 

SPS takes two different conformations in its crystal, TT and TTGG conformations, depending on the crystallization conditions, and exhibits a very complex polymorphic structure [6-14]. One is the TT conformation which appears when SPS crystallizes from the melt. Two different transcrystals are reported when SPS takes the TT conformation in the crystal, a-form [15-19] and 3-form. The identity period is 5.06 A (Figure 18.3) in both crystal forms. The 3-form is more thermally stable than the a-form. Figure 18.4 shows the detailed structure of the 3-form [6,10]. 

SPS takes the TTGG conformation when it crystallizes in the presence of organic solvents. SPS takes the TTGG conformation in -y-form and 8-form crystals. The 8-form is a complex of SPS and solvent [20-24], Figure 18.5 shows the complex of SPS and toluene. 

An example of this is syndiotactic poly(propylene). The ir spectrum has a pronounced crystalline band at 868 cm" for the stablest crystalline state. According to theoretical considerations, this band, (see Figure 4-10), is practically entirely due to helical (TTGG) conformations. The band disappears on melting. 

Figure 3 shows the infrared spectra of the phenyl out-of-plane mode of sPS and sPPMS, before and after soaking in phenol solution. The peaks characteristic of the ttgg conformation at 572 cm i and 566 cm i for sPS and sPPMS are well-known to be very sensitive to the conformation. These peaks increased in intensity for both cast-crystaUized and melt-quenched films after soaking in phenol solution. This is direct evidence that the crystal with a ttgg conformation was induced by the presence of phenol. 

Raman (wavenumber-assignment) cmV- frans-planar chains - 2917, 2845 TTGG conformation - 2850 Zheng, K Liu, R Kang, H Gao, X Shen, D Huang, Y, Polymer, in press, 2011. 

Figure 1 Effect of annealing time and temperature on chain conformation in annealing time and temperature. Ri and Rz characterize the relative amounts of polymer in the TT and TTGG conformations, respectively.

Figure 11 indicates that Eq. (9) holds at any temperature. The value of p, which is obtained from the slope of the straight Unes, depends on temperature. For example, p = 5.2 at 10°C. This indicates that approximately five segments are gathering to stabilize the TTGG conformational chain order. As the temperature reduces, the value of p, that is, the number of the segments necessary to stabilize the TTGG conformational chain order, decreases. This number becomes 1 below — 15°C (see Fig. 12). 

The highly stereoregular syndiotactic polystyrene (s-PS) has received considerable interest recently. Depending on the thermal history, s-PS possesses several polymorphie erystalline structures. Helical (TTGG) conformation is formed in solution reeovered s-PS, whereas the thermodynamically favored all-trans (TTTT) eonformations are formed from either melt or annealing at an elevated temperature. The extent to which thermal history affects the crystalline strueture and erystallization kinetics for s-PS has been extensively studied. ... 

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