Molecular weight data

Table 1.4 Some Classified Molecular Weight Data for a Hypothetical Polymer Used in Example 1.5...

This contrasts with a limiting ratio of 2 for the case of termination by disproportionation. Since and can be measured, this difference is potentially a method for determining the mode of termination in a polymer system. In most instances, however, termination occurs by some proportion of both modes. Although general expressions exist for the various averages and their ratio when both modes of termination are operative, molecular weight data are generally not sufficiently precise to allow the proportions of termination modes to be determined in this way. 

Analytical information taken from a chromatogram has almost exclusively involved either retention data (retention times, capacity factors, etc.) for peak identification or peak heights and peak areas for quantitative assessment. The width of the peak has been rarely used for analytical purposes, except occasionally to obtain approximate values for peak areas. Nevertheless, as seen from the Rate Theory, the peak width is inversely proportional to the solute diffusivity which, in turn, is a function of the solute molecular weight. It follows that for high molecular weight materials, particularly those that cannot be volatalized in the ionization source of a mass spectrometer, peak width measurement offers an approximate source of molecular weight data for very intractable solutes. 

Errors in the molecular weight data from HPSEC are usually due to improperly prepared samples, column dispersity, or flow rate variations. The sample to be analyzed should be completely dissolved in the mobile phase and filtered prior to injection onto the column. A plugged column inlet frit will invalidate results. In addition, do not load the column with excess sample. Column overloading affects the accuracy of data by broadening peaks, reducing resolution, and increasing elution volume. For best results, the concentration of the injected sample should be as low as possible while still providing adequate... 

Compounds with structure 9 have been obtained by oxidative coupling of 4-alkyloxazolones, using mercuric acetate, as shown in Eq. (6). The structure was deduced from molecular weight data. 

The nature of the termination reaction in MMA polymerization has been investigated by a number of groups using a wide range of techniques (Tabic 5.5), There is general agreement that there is substantial disproportionation. However, there is considerable discrepancy in the precise values of k tk. In some cases the difference has been attributed to variations in the way molecular weight data are interpreted or to the failure to allow for other modes of termination under the polymerization conditions (chain transfer, primary radical termination).154 In other eases the reasons for the discrepancies are less clear. MALDI-TOF mass... 

The molecular weight data in this paper will be discussed in detail in the subsequent paper ... 

PIB s prepared with r-BuBr/Et2AlCl/MeCl show similar characteristics. Figure 2 and Table 2 show the molecular weight data obtained in the range from —30° to -60 °C. M and Mw of the total polymer show some scatter, though Mw and MWD tend to increase with decreasing temperatures. The data obtained at -45 °C, Le., the exceptionally high M and Mw, are difficult to explain. 

Figure 3 and Table 3 give the data for PIB prepared with f-BuCl/Et2AlBr/MeBr in the range from -30° to -65 °C. All GPC traces are monomodal, even for samples prepared below -50 °C (an exception was the sample prepared at -65 °C, which showed a small shoulder). While the molecular weight data are scattered and a trend... 

Both types of complex are extremely air-sensitive and are paramagnetic, with one unpaired electron per titanium atom. Their formulation as monomeric, symmetrical, bidentate, chelate complexes, (IV) and (V), has been established from spectral, magnetic, and molecular-weight data. 

This sometimes complicates the extraction of molecular weight data as it is not always immediately clear which ions in the spectrum originate from each component. This can be determined by the use of equation (4.6). An example of this is shown in Figure 4.18, which shows the electrospray spectrum from what is apparently a single chromatographic response, while Table 4.3(a) displays the results of applying equation (4.6) to the major ions found in that spectrum. As... 

In the previous section, the generation and processing of molecular weight data from electrospray spectra have been described. The other great strength of mass spectrometry is its ability to generate structural information from the analyte... 

The PCP (Aldrich, catalogue no. 18,168-4, lot no. 03) had no listed molecular weight data. A broad MMD polystyrene (PS) standard (National Bureau of Standards) had a light scattering fl = 257,800 (SRM 706, R7R =2.1). Six of the narrow MMD PS standards (Pressure ChemTcaT Co.) had nominal molecular weights... 

Table I shows molecular weight data obtained from SEC/LALLS measurements on the narrow MWD polystyrene standards. Bandspreading correction of the ft values generally resulted in a decrease in fl of 1% to 4% Below the value directly obtained from treatment 8f SEC/LALLS data with the MOLWT program.

The second method assumes that the molecular weight calibration curve is linear on a semilog plot and should be employed where universal calibration is not practical as with aqueous SEC. Several variants of these methods involving different molecular weight data for the standards are discussed. The proposed methods have been evaluated using aqueous SEC and polydextran standards and nonaqueous SEC with polyvinylchloride standards. 

Two Pieces of Molecular Weight Data Per Standard. This method uses the fact that when equations (la) and (2a) or (la) and (3a) with proper modification are multiplied the peak broadening parameter vanishes. The equations for two broad MWD standards where M and M are known follow ... 

One Piece of Molecular Weight Data Per Standard. With this amount of molecular weight information per standard, one should estimate the peak broadening parameters (a ) for each standard using narrow MWD polystyrene standards. With this method there are various possible combinations of molecular weight data, Mj, and [q]. follow ... 

There are many additional combinations which may be employed. Any of these combinations of molecular weight data permit a singlevariable search for a followed by a direct calculation of K. 

The molecular weight data for the two broad MWD PVC standards used in this investigation of universal calibration are given in Table... 

Figure 2. Intrinsic viscosity-molecular weight data for polystyrene and polyvinyl chloride measured by osmometry and by SEC using broad MWD standard calibration (polystyrene (m) M = 7,06 X 10 in THF/1% PPG (O) [ ] =...

The third class of polymers contains one or more nitrogen atoms on a pendant sidechain in the polymer repeat unit (13,14). The nitrogen may or may not be quaternary. In addition to being swelling clay stabilizers, these polymers also stabilize nonswelling mineral fine particles. Limited molecular weight data ig available but molecular weight values from 50,000 to 1 X 10 daltons have been cited for various polymers. 

Figure 5. Initiator loadings (O) Experimental values ( ) Calculated from the molecular weight data and the assumption of two end groups per molecule (1) Calculated from Case I efficiencies (2) Calculated from Case II efficiencies (3) Calculated from Case III efficiencies.

Confirmation of the modification of the hydroxyl end groups from the PPG can be accomplished by analysis using MALDI-TOF MS [59]. An example MALDI-TOF mass spectrum of a prepolymer based on PPG 2000 is shown in Figure 28. End group and average molecular weight data can be gleaned from the spectrum. The dominant distribution of peaks centred at approximately m/z 2,500... 

Figure 13.1 Dependence of the hardness of linear polyethylene on its molecular weight. Data from Balta-Calleja et al., (1990).

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