Oligomers, fractionation

Fig. 3. Graph based on an hplc chromatogram of a commercial PTMEG of molecular weight = 1000. The bars represent the weight percentage of the individual oligomer fractions. The degree of polymerization is the number of repeating monomer units per polymer chain.

Polyn rization times and yields are given in Table I. The pol3rmers and oligomer fractions are designated according to the batch or lot number of the trimer from which they were derived. 

Occasionally there is the need for simultaneous determination of MW, MWD of polymers and identifica-tion/quantilication of additives [38]. This was the case for polymer and additive analysis of SBR/(softeners, flavour agents, stabilisers) (chewing gum) [41]. The many constituents of the SBR portion of the sample were not resolved, since adjacent components were similar in size. It should be stressed, however, that the need for simultaneous determination of the molecular weight of polymers and the identification/quantification of additives is exceptional rather than the rule. The determination of molecular weight distributions by SEC has indicated that oligomer fractions analysed by dissolution and (Soxhlet) extraction methods may differ essentially [42],... 

The contour plot clearly shows five spots corresponding to the five functionality fractions, compared to Fig. 17.6, with fraction 2 being the main fraction containing the a-octylphenoxy-co-hydroxy oligomers. In addition, a,CO-di(octylphenoxy) oligomer fractions and fractions having butylphenoxy end groups are obtained. It is obvious that the fractions have very similar molar masses. 

To resolve the linear oligomer fractions, Weidner et al. (2004) proposed an alternative approach. He used the combination of LCCC and MALDI-TOF to identify the different functionalities. Weidner performed a separation according to chemical composition by LCCC, and used a spray interface (LC-Transform from LabConnections) to deposit the chromatographic fractions on a MALDI-TOF target. In the second step, each individual... 

Fractions of the higher molecular weight, more complex reaction products were obtained by the preparative SEC of further advanced TGMDA/DDS reaction mixtures. For example, the proposed components of the next highest oligomer fraction are the 3-1, 2-2, and 1-3 TGMDA-DDS products. The relative ratio of the products depends upon the initial composition of the TGMDA/DDS resin formulation. 

Research on model compounds and sharp oligomer fractions has already had a profound effect on our understanding of polymer crystallization and morphology. The availability of monodisperse polymers removes the dependence of this field of science on essentially impure multicomponent experimental systems. It also helps close the gap between polymer science and mainstream chemistry and physics. 

NMR spectra of oligomer fractions a (dimers), b (trimer), c (trimers), d (tetramer), e (tetramers), f (pentamer). 

The next attempt at these reactions were carried out by Yamamoto et al. [26], They coupled 2,7-dibromo-9,10-dihydrophenanthrene to give an ethano-bridged poly(p-phenylene) derivative [poly(9,10-dihydrophenanthrene-2,7-diyl)] (9) by way of low-valent nickel complexes, which were used either stoichiometrically as reagent (Ni(COD)2) or were generated electrochemically in the reaction mixture. As a result of the insufficient solubilization of the ethano substituents only the oligomer fraction with Mn<1000 is soluble, the polymeric products precipitating out as an insoluble powder. The value of for the soluble fraction of 9 is about 360 nm. 

C-NMR studies of these polymers showed that the spectrum of the oligomer fraction had very complicated features owing to the irregular structure admixed with head-to-head and tail-to-tail enchainments of the monomeric unit, which again is in sharp contrast with the clear-cut NMR patterns for the polymers prepared with the one to one catalyst system. 

Figure 5.4 I3C-NMR spectrum of the oligomer fraction obtained by PE catalytic degradation over amorphous silica-alumina.13...

The copolymer prepared by Hammond et al. 33), under essentially the same conditions, had different characteristics. GPC analysis showed bimodal molecular weight distribution, besides a high-molecular-weight polymer an oligomer fraction was also formed. The latter consisted mainly of cyclic PO tetramer but mixed (PO and THF) tetramers and pentamers were also identified. The M determined by GPC was low (usually below M = 500). The OH end-groups were determined by acetylation with acetic anhydride in pyridine with HC104 catalyst. 

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