Polystyrene as standard

In most cases PAEs have been characterized by either light scattering or GPC with polystyrene as standard. The values obtained by GPC experience the same systematic error, i.e., overestimation of the molecular weight as discussed for the PPEs. However, PAEs, which deviate from linearity, display a more coiled conformation in solution, and a better match of the real molecular weights with the ones obtained by GPC is expected. 

Molecular weights were measured on a 150 ALC/GPC, Waters Associates, Inc., using polystyrenes as standards for molecular weight and separation. No corrections were made so that the distributions may be slightly more narrow than reported. 

The structure of this copolymer was characterized by IR, and NMR, GPC, DSC, and TGA. The composition of the poly(TSE-co-4FST) copolymer was calculated from nitrogen analysis (%N = 7.22%), the molar percentage of cyano monomer (TSE) was closed to 38%. The molecular weight calculated from SEC using polystyrenes as standards was around 8000 g/mol. 

Af , Afw and MJM were obtained from SEC measurements by using narrowly distributed polystyrenes as standards... 

Figure 9.7 shows separations under identical conditions using PSS SDV columns with 3 (Fig. 9.7a)-, 5 (Fig. 9.7b)- and 10 (Fig. 9.7c)-/i,m particle size columns. A polystyrene oligomer standard was injected and all analyses were performed in THF as the eluent. The much higher efficiencies of small particle size columns are obvious, which is important in the SEC separation of low molecular weight compounds such as additives, by-products, and resins. The reader should note that all chromatograms are area normalized and have the same Y axis to show the differences in peak width and height. 

Determinarion of MW and MWD by SEC using commercial narrow molecular weight distribution polystyrene as calibration standards is an ASTM-D5296 standard method for polystyrene (11). However, no data on precision are included in the 1997 edition of the ASTM method. In the ASTM-D3536 method for gel-permeation chromatography from seven replicates, the M of a polystyrene is 263,000 30,000 (11.4%) for a single determination within the 95% confidence level (12). A relative standard deviation of 3.9% was reported for a cooperative determination of of polystyrene by SEC (7). In another cooperative study, a 11.3% relative standard deviation in M, of polystyrene by GPC was reported (13). 

Most frequently, SEC with dextran-, pullulan-, or polystyrene calibration standards has been used to characterize the molecular properties of xylans. However, as for viscometric studies [108], a sufficient solvent ionic strength is a prerequisite for useful SEC measurements of charged polysaccharides, including glucuronoxylans [111-113]. An advantage of the SEC technique is that the presence of protein and phenolic components or oxidative changes can be detected by simultaneous ultraviolet (UV) detection. 

Heller and Tabibian (13) noted that errors, due to laterally scattered light and the corona effect, as large as to cause a 30 reduction in measured turbidity, may result if instruments which are perfectly suitable for ordinary absorption measurements are used for turbidity measurements without proper modifications. To evaluate the performance of our turbidity detector, particle suspensions of various concentrations of several polystyrene latex standards were prepared. Their extinction coefficients were measured using both a bench-top UV spectrophotometer (Beckman, Model 25) and the online detector (Pharmacia). 

Conjugated boron polymers containing platimnn or palladium atom in the main chain were also prepared by hydroboration polymerization between tetrayne/ metal complex monomers and tripylborane (scheme 16).30 From gel permeation chromatographic analysis [THF, polystyrene (PSt) standards], the number-average molecular weights of the polymers obtained were found to be 9000. The polymers were soluble in common organic solvents such as THF, chloroform, and benzene. The absorption peaks due to tt-tt transition were observed around 390 nm in the UV-vis spectra of these polymers. The fluorescence emission spectra exhibited intense peaks at 490 nm in chloroform. 

Carefully constructed Probe Mixtures based on small molecules and polystyrene standards are used as standardized reference points to better define the functional capabilities of individual columns and column combinations. The result using the method of Probe Mixtures to evaluate columns is better than can be attained from calibration curves alone and is especially useful in this high resolution capability situation. 

Estimation of Molecular Weight Distribution of Polyamide Blocks. The molecular weight distribution of the polyamide blocks was estimated by gel permeation chromatography (GPC) using two instruments, model HLC-802R (Toyo Soda Industry Co., Ltd.) and model GPC-2i U (Waters Associates, Inc.). Polystyrene and nylon oligomer were used as standards. 

Since no adequate SEC standards were available, linear polystyrene was used as standard. As expected, the determined molar masses were not in agreement with the theoretical molar masses. This could be explained by the differences in hydro-dynamic volume between linear polystyrene standards and the dendritic polyesters. SEC analyses showed polydispersity values (A/ /M ) below 1.02 for dendrimers Dl, D2, and D3, which was the maximum resolution of the column (Table 2, Figure 4). 

Preparation of the Living" Polystyrene. 18 g of the living polymer was prepared by standard anionic polymerization using n-butyl lithium. The reaction was carried out by the dropwise addition of 20 ml of styrene to 5 ml of the initiator solution in 150 ml of neat THF at -78°C. The styrene drip was adjusted to take approximately 30 min for completion and then the reaction was allowed to stir for two hours before the grafting reaction with mesylated lignin was carried out. The number average molecular weight of the polystyrene, as determined by HPSEC, was 9500 with polydispersity of 1.2. 

Monodisperse spheres are not only uniquely easy to characterize, but also very rarely encountered. Polymerization under carefully controlled conditions allows the preparation of the polystyrene latex shown in Figure 1.8. Latexes of this sort are used as standards for the size calibration of optical and electron micrographs (also see Section 1.5a.3). However, in the majority of colloidal systems, the particles are neither spherical nor monodisperse, but it is often useful to define convenient effective linear dimensions that are representative of the sizes and shapes of the particles. There are many ways of doing this, and whether they are appropriate or not depends on the use of such dimensions in practice. There are excellent books devoted to this topic (see, for example, Allen 1990) and, therefore, we consider only a few examples here for the purpose of illustration. 

The polystyrene seed latex was monodispersed. Even after several grow-ups (polymerizations) the final 1650 A latex was monodispersed. Hydrodynamic chromatography on the 1650 A latex gave a mean diameter of 1660 a with a size variance as small as for normal polystyrene latex standards (typical standard of 1760 8 with a standard deviation of 23 a). The final latex particle size could be accurately predicted from the initial particle size and the total amounts of monomer and polymer used. 

As in the case of terpyridine-based polymers, we first reported the application of Zn(II) Schiff base polymers in PLEDs.33 We prepared a family of soluble self-assembled Zn(II) Schiff base polymers, which are thermally stable, structurally diverse and easily modified (Fig. 17). The number-average molecular weight (Mn) of the polymers range from 13580 to 20440, as determined using gel permeation chromatography (GPC) with polystyrene as a standard in THF (tetrahydrofuran) at 35°C. The decomposition temperature (Td) of the polymers range from 389° (2g) to 461°C (2h). No phase transition was observed in DSC up to 300°C for these polymers (Table 4). 

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