Blend samples

The refractograp of figure 4 shows highly oriented micro cracks of a polystyrene sample. The orientation of the cracks is perpendicular to the mechanical strain direction. The X-ray refracted intensitiy can be interpreted as crack density, i.e. the inner surfaces within a unit volume. Changing the tilt angle (of polystyrene and polystyrene blend samples) with respect to the primary beam leads to significantly different distributions of crack orientation (Fig. 5). 

In a molded polymer blend, the surface morphology results from variations in composition between the surface and the bulk. Static SIMS was used to semiquan-titatively provide information on the surface chemistry on a polycarbonate (PC)/polybutylene terephthalate (PBT) blend. Samples of pure PC, pure PBT, and PC/PBT blends of known composition were prepared and analyzed using static SIMS. Fn ment peaks characteristic of the PC and PBT materials were identified. By measuring the SIMS intensities of these characteristic peaks from the PC/PBT blends, a typical working curve between secondary ion intensity and polymer blend composition was determined. A static SIMS analysis of the extruded surface of a blended polymer was performed. The peak intensities could then be compared with the known samples in the working curve to provide information about the relative amounts of PC and PBT on the actual surface. 

The second example, a blend sample consists of 80% PA 6.6, 18% PTFE and 2% silicone oil. From the relative concentrations, it can be seen that PA forms the matrix and provides the necessary stability to the bearing. PTFE acts as an incorporated lubricant. The two main components are not chemically linked. Therefore, silicone oil has been added to work as a boundary lubricant during the break-in phase of the bearing. Due to its liquid nature, it quickly migrates to the surface when pressure is applied and prevents abrasion at the first stage. Shortly after, a thin film of PTFE forms at the interface between the thermoplastic bearing and the counter part. 

The GPC traces in Fig. 24 reveal a broad molecular weight distribution, MJMn = 4.42, for the dual reactor blend sample. On the other hand, the diblock OBC displays an overall MJMn of 1.67. The narrowing of the distribution indicates that the polymerization has CCTP characteristics. The theoretical molecular weight distribution from an ideal living polymerization in a series of two CSTR reactors is given by the following equation, where/j and/2 are the mass fractions of polymer comprising the two blocks [11] ... 

Fi sh Soxhlet extraction of Qui ntani11a- blended sample clean-up... 

For a statistical analysis to adequately characterize the distribution of a component, the data should first be processed to obtain the optimum selectivity for that component. In this application the PLS model produces a score image that effectively separates the spectral response of the API from the excipients. Even though there is very little observable contrast in the images of the well blended samples, the results from the poorly blended samples convey conhdence that the method is effective at tracking the API distribution. 

From such a background, some kinds of polypeptide blend samples have been studied by solid state NMR.27,72 74 Especially, detailed information for four kinds of blend samples such as poly(L-alanine) (PLA)/poly(L-valine) (PLV), PLA/poly(L-isoleucine) (PLIL), poly(D-alanine) (PDA)/PLV and polyglycine (PG)/PLV blends, have been reported. Here, let us describe some reasons why PLA/PLV, PDA/PLV, PLA/PLIL and PG/PLV blends are interesting systems. PLA and PDA in the solid-state can take the a-helix and (3-sheet forms due to intra- and intermolecular HBs, respectively. PG in the solid-state can take the 3j-helix (PG-II) and (3-sheet (PG-I) forms due to intra- and intermolecular HBs, respectively. However, PLIL and PLV in the solid state can predominantly take the (3-sheet form as the stable conformation. For this reason, it is interesting to know whether an isolated a-helix or 3i-helix form polypeptide surrounded by a major polypeptide in the (3-sheet form can take the helical conformation, or not, due to the balance between intramolecular and intermolecular hydrogen bonds. In addition, we would like to know whether a polypeptide in the (3-sheet form surrounded by a major polypeptide in the a-helix or 3 -helix form can take the (3-sheet form. 

Some kinds of polypeptide blend samples (PLA/PLV, PLA/PLIL, PG/PLV and PDA/PLV) have been treated with different blend conditions, and their miscibility has been investigated by the observation of 13C NMR chemical shifts and 3H 7) data.17 27 Furthermore, we need more detailed information about the miscibility of the polypeptides to understand the polypeptide blend by using further sophisticated NMR methodology. Thus, 2D FSLG 13C- H HETCOR NMR is useful to elucidate intermolecular HB interactions between two kinds of polypeptide chains and their miscibility. 

On the other hand, the deposition process is also important to prepare blend samples. A mixture of homopolypeptide solutions in which they take a random coiled structure are added into a poor solvent. For polypeptides, water is a poor solvent in general. If the hydration rate is different for each polypeptides, they form their preferred secondary structures by themselves and then do not blend with each other. On the basis of this assumption, in order to make the hydration at the same time, the solution is added to alkaline water. In this review, two kinds of quieting solvents such as water and alkaline water have been used. (Methods 1-4 and Method 5). Method 1 Helical polypeptide and (3-sheet polypeptide are dissolved in DCA and agitated... 

In order to elucidate the conformational characterization of PLA/PLV blend samples obtained by using the four methods as mentioned above, solid-state 13C NMR measurements are made on the blend samples. 

Furthermore, the observed 13C CP/MAS NMR spectra of PLA, PLV and PLA/PLV blend samples obtained by Method 4, with various mixture ratios, are shown in Fig. 4. The assignments of these spectra are made using reference data reported previously.21,22,26 The 13C chemical shift values of these polypeptide samples are listed together with reference data in Table 4. In the spectrum of PLA (Fig. 4a) we can assign peaks to the C=0, Coe and Cp carbons, respectively. From the 13C chemical shift values, it is found that PLA takes the right-handed a-helix form. On the other hand, in the spectrum of PLV (Fig. 4e) we can assign peaks to the C=0, Ca, Cp and Cy carbons,... 

Table 3. Observed solid-state 13C chemical shifts of pure PLA, pure PLV and PLA/PLV blend samples obtained by Methods 2 and 3...

If we look at the spectra carefully, another new peak of the Cp carbon of PLA appears at about 21.1 ppm, in addition to an intense peak assigned to the a-helix form (16.0 ppm), and can be assigned to the p-sheet form (21.1 ppm) by using reference data. These results show that the a-helix form of PLA in the PLA/PLV blend samples are partially transformed to the p-sheet form. 

It is very significant to state that if only PLA is treated by TFA alkaline water (Method 5), then PLA does not change its conformation. Nevertheless, when PLA/PLV blend samples prepared by the same treatment are used then, the p-sheet form is formed. The origin of the formation of the p-sheet form in PLA comes from the existence of PLV. Therefore, it can be said that the p-sheet form of PLA in the PLA/PLV blends is incorporated into the PLV with the p-sheet form and then takes the p-sheet form by forming intermolecular interactions with PLV. Another component of PLA remains in the a-helix form, and the p-sheet form of the PLA chains intermolecular interactions with PLV chains is much more stable than the a-helix form of the PLA chains themselves. Thus, the generation of same conformations of PLA in PLA/PLV blends may be closely associated with... 

Fig. 5. 13 CP/MAS NMR spectra of PLA ( ), PLV ( ) and PLA/PLV blend samples which were prepared by adding their TFA solutions with a 2.0 wt/wt% amount of H2SO4 to alkaline water (Method 5). Homopolypeptides of PLA (a-helix) and PLV (P-sheet) are prepared using same condition as PLA/PLV (80/20, 50/50, 20/80) blend samples. The symbols of starpA) show the new signals that were produced by this blend condition, (a) PLA, (b) PLA/PLV (80/20), (c) PLA/PLV (50/50), (d) PLA/PLV (20/80) and (e) PLV.

Fig. 6. Expanded 13C CP/MAS NMR spectra for the carbonyl-carbon region and for the Ca, Cp and Cy carbons region of PLA/PLV (50/50) blend sample.

By computer-fitting the observed spectrum was decomposed to a sum of Lorentzian lineshapes, and then the fractions of the a-helix and p-sheet forms for PLA and PLIL were determined. The PLA/PLIL blend sample with a mixture ratio of 50/50 (wt/wt%) corresponds to the molar mixture ratio... 

The observed 13C CP/MAS NMR spectra of PG, PLV and the PG/PLV (20/80, 50/50 and 80/20 wt/wt%) blend samples as prepared by adding a TFA solution with a 2.0 wt/wt% amount of H2S04 to alkaline water (Method 5) are shown in Fig. 10. In the 13C CP/MAS NMR spectra, homopolypeptides of PG (3i-helix) and PLV ((5-sheet) are prepared using the same conditions as for PG/PLV blend samples. The assignments of these spectra were made by the above-mentioned method. The 13C chemical shift values of these blend samples are listed together with those for PG in the 3i-helix form (PG-II) and the p-sheet form (PG-I), and PLV in the p-sheet form in Table 7.21,22,26 The two intense peaks at 172.9 and 42.9 ppm, which appear in the spectrum of PG (Fig. 10 a) can be assigned to the C=0 and Ca carbons. From these 13C chemical shift values, it is found that the PG used in this work takes the 3 -helix form. There are no peaks which come from the p-sheet form. On the other hand, in the spectrum of PLV (Fig. 10 e), the four intense peaks appear at 172.0, 58.6, 32.8 and 19.0 ppm and can be assigned to the C=0, Ca, Cp and Cy carbons, respectively. From these 13C chemical shift values, it is found that PLV takes the p-sheet form. 

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