Oligomer series

The separation on gel beads was more and more refined. Oligomer series of many polyhexapeptides from n = lton = 9 could be completely separated16,20 24) (see Fig. 4). The hexapeptide oligomers could be separated better than the respective tripeptides. 

Table Chain length L(inA°) in the four oligomer series...

There are two different oligomer series present in all spectra. The oligomer series can be identified by calculating the masses of the end groups and assigning them to specific chemical structures (Pasch and Schrepp, 2003 Weidner et al., 2004). In the present example, the two species are the propionic amide-acid (R-am-ac) and the propionic amide-propionic amide polyamides (R-am-am-R). The use of MALDI-TOF MS as a structure-sensitive detector allows the resolution to be indirectly enhanced since several species coelute, as shown in Fig. 17.21. The polarity of the... 

Figure 4.5. Solution- and solid-phase oligomer yields versus length for the indicated oligomer series.

The pure TMS and TES polytriacetylene oligomer series were investigated including a polymer sample. The different end groups in the polymer have a negligible influence on the molecular property as the PTA backbone is long enough to dominate the molecular properties. 

The relationship between Tg and molecular weight, M, is often described by the Fox and Flory equation 266 Tg = T/XJ - K/M, where T/XJ is the glass transition temperature of the polymer with infinite molecular weight and K is a constant characteristic of the polymer. For the malto-oligomer series, a double reciprocal plot of... 

Figure 53. Cisoid— transoidequilibrium of 2,2 -bipyridine and the structure of oligomer series 11 (n = 2, 5, 8, 9, 12).

All members of oligomer series 24 were fully substituted with chiral side chains, not allowing the... 

These results continue to support the hypothesis that all members of oligomer series 23 exist in solution in conformationally well-ordered states with chiral cylindrical cavities capable of binding chiral rodlike guest molecules such as 39. Co-modularity of host—guest oligomeric pairs such as the system described here raises a number of engaging possibili-... 

TIC chromatogram (bottom chart) and contour plot for the LC-ESI-MS analysis of Triton X-100, by using gradient reversed-phase chromatography [2 mm i.d. octadecylsrUca column, 20/80 to 50/50 acetonitrile/10 mM ammonium acetate in 20 min, 200 /iL/min flow rate, 3 1 effluent split, nebulizer-assisted electrospray]. See Figure 4.9 for the oligomer series (I-IV) separated. (Courtesy of PE Sciex, Foster City, CA)... 

A typical Py-FI mass spectrum for a hydrocarbon polymer (isotactic polypropylene) is shown in Figure 6.9 TTie spectrum shows the initial pyrolyzates that are formed as the polymer is held at 400°C in the direct probe. Volatile pyrolyzates are observed at every carbon number up to -1400 Da (Cioo). It is interesting that the principal oligomer series at low mass is simply multiples of the propylene monomer xmit (MW = 42n, series A). The principal series at higher mass values, however, is an a, -diene series (MW = 42n -l-12, series E). The pyrolysis mechanism may be explained by a free radical degradation pathway. ... 

In fact, even for the simplest homopolymers one often experiences several mass peaks due to oligomer series having the same repeat unit but different end-groups. 

The FAB mass spectra obtained for some (PHB-co-HV) copolymers allow the identification of oligomer series up to hexads. A comparison between the experimental and the calculated peak intensities shows a clear distinction... 

Comparison of calculated and observed duster structures for poly(ethylene adipate). Oj is the oligomer series, is a fragment having an integral number of repeat units. (Reprinted with permission from Ref. 47, Copyright 1994 American Chemical Society)... 

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