GPC calibration

Hydrodynamic volume of polymer (here considered equivalent to the separation parameter KM Table II for GPC calibration)... 

The polymerization was carried out in THF under the conditions of high vacuum or argon atmosphere with a catalytic amount of alkyllithium as an initiator. Anionic polymerization of 3a with n-BuLi in THF followed by quenching with ethanol afforded polymer 6 in 56 % yield. The molecular weight distribution of the polymer was determined by gel permeation chromatography (GPC), calibrated by polystyrene standards, with chlorofrom as eluent Mn = 6.1xl0"4, Mw/Mn = 1.3. 

In examining these GPC data it should be noted that the averages and the Mz/Mn ratios are meant only to convey qualitative information about scission and branching owing to the problem of GPC calibration not being for branched molecules like those being produced [8],... 

GPC calibration curves are established based on the radius of gyration of known-molecular-weight polymers, such as well characterized, narrow-molecular-weight distribution polystyrene. Branched polymers have a lower radius of gyration for their molar mass than the corresponding linear molecule. Thus, as branching increases the GPC numbers become less and less accurate and so should only be used for trends, and not exact calculations as some authors have done. 

The hmax obtained from the GPC calibration curve by estima-... 

Figure 1. Schematic for GPC calibration subject to Poisson constraints.

Determination of Pore Size Distributions. The shape and range of a GPC calibration curve are, in part, a reflection of the pore size distribution (PSD) of the column packing material. A consideration of the nature of PSDs for the ULTRASTYRAGEL columns to be used in this work is therefore appropriate. The classical techniques for the measurement of PSDs are mercury porisimetry and capillary condensation. The equipment required to perform these measurements is expensive to own and maintain and the experiments are tedious. In addition, it is not clear that these methods can be effectively applied to swellable gels such as the styrene-divinylbenzene copolymer used in ULTRASTYRAGEL columns. Both of the classical techniques are applied to dry solids, but a significant portion of the pore structure of the gel is collapsed in this state. For this reason, it would be desirable to find a way to determine the PSD from measurements taken on gels in the swollen state in which they are normally used, e.g. a conventional packed GPC column. 

While the effects of flow rate drift or noise at the one percent level over the duration of the separation are not nearly as disastrous as the case illustrated in Taible VI, the data serve to demonstrate the need for flow rate staibility and repeatcibility. The cibsolute accuracy of flow rate is of lesser importance, as this type of variation only manifests itself when comparing raw data obtained on different instruments, all of which should be calibrated independently of each other in any case. It should be pointed out that the GPC calibration should always be redetermined whenever any component of the system is changed this is simply good leiboratory practice. 

The use of a continuous GPC viscosity detector in conjunction with a DRI detector permits the quantitative determination of absolute molecular weight distribution in polymers. Furthermore, from this combination one can obtain Mark-Houwink parameters and the bulk intrinsic viscosity of a given polymer with a GPC calibration curve based only on polystyrene standards. Coupling these two detectors with ultraviolet and infrared detectors then will permit the concurrent determination of polymer composition as a function of molecular weight and... 

Figure 2 shows a co hvent i ona 1 GPC calibration curve for the standards, that is, a plot of GPC retention vs log M. These dat.a were fitted to a Fth order polyriomial and the molecular weights of all the standards recomputed from this fit using the measured retention volumeis. These values are shown in column 7 of Table I. 

NMR end group [OCH(CH3)2] analysis, were used as standards for GPC calibration for... 

In addition, hydroxyl polymers prepared by use of lithium alkyl acetal initiators have shown a high degree of functional purity (Table II). The functionality data for XI is a bit low, in part, because a linear GPC calibration was used to calculate nn (GPC). It should also be noted that Equations 1-9 proceed in the absence of anionic association or gel. 

This is the case of parallel calibration curves discussed in the previous paper. Equation 4 shows that when the calibration curves are parallel, the equivalence ratio, r, is constant to the elution volume V. It varies with the latter when aA aB—i.e., the calibration curves are not parallel. For that case Equation 3 would have to be used. Equation 4 also shows that the equivalence ratio can be calculated from the Mark-Houwink parameters K and a. It offers a way to determine r in addition to obtaining it from the GPC calibration curves of homopolymers. 

Figure I. Plot of GPC calibration data showing the relationship of the number-average molecular weight vs. the elution volume (counts) of the...

Moreover, no general valid mathematical expression is available for the GPC-calibration curve because the GPC-resolution mechanism has not yet been described mathematically to a sufficient extent. However, as the GPC-calibration curve is temperature-independent, spline polynomials 16) can well be used here, or a 4-para-meter-formula propsed by Yau and Malone 281 can be applied (cf. also the papers of Rosen and Provder quoted in Ref. 27i). 

C6Hj-N = N-C(C6H5)2(OCOCH3) b By membrane osmometry, PM AN = poly(methacrylonitrile) c By GPC, calibrated with polystyrene standards d Grafting efficiency (see Sect. 3.2.7)... 

BPF, which has low solubility in both water and organic liquids, was used. Phosgene was bubbled into the chloroform/water/salt slurry, and sodium hydroxide was added at a rate to maintain pH 10.5. Gel permeation chromatograms of these polymers showed a bimodal distribution the smaller peak was attributable to cyclic carbonates (1-10% ). Soxhlet extraction with dimethoxymethane reduced these to 1% or less, and subsequent to extraction Mw/Mn = 2.5-3.5 apparent Mn s (based on a polystyrene GPC calibration) were 25,000-50,000. (Corresponding osmo-metric molecular weights are roughly one-third greater.)... 

Figure 2. GPC calibration curve using Dextran T standards.

Figure 2. GPC Calibration Plot for TGMDA-DDS Reaction Products.

Most likely, M curves downward early because the GPC calibration is no longer applicable at relatively high extents of reaction... 

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