Polystyrene-equivalent molecular weights

GPC analyses were performed with a Waters Model 244 chromatograph using Microstyragel columns. Both differential refractive index and UV (254 nm) detectors were used. THF was the eluant with a flow rate of 2 ml min-1. A benzene internal standard was employed to correct for flow variations and for normalization of the integrated peak areas. The column set was calibrated using nearly monodispersed polystyrene standards and all molecular data are reported as polystyrene-equivalent molecular weights. 

Not unexpectedly in view of their composition that includes two globular A components, the polystyrene equivalent molecular weights of the ABA structures, as assessed by SEC, were lower than expected [38-40]. Although this is... 

In a previous report (30), we found that n-hydrocarbon standards are useful to extend the range of (small) pore sizes which may be probed. Polystyrene-equivalent molecular weights (MWp) are assigned to each hydrocarbon using the empirical relationship (31) ... 

Molecular weight and polydispersity were determined by gel permeation chromatography. The values reported are in terms of polystyrene equivalent molecular weights. 

Copolymerization of I with styrene. A glass ampoule was charged with 1.45g (5m mol) of 1,0.53g (5m mol) of styrene, and 33 mg of AIBN (2 mol %) dissolved in 2.0 ml of dioxane. The ampoule was sealed under vacuum after a freeze-thaw cycle and the copolymerization was carried out at 58°C for 3 hours. The jelly-like polymer mixture was dissolved in NMP and the polymer was isolated by precipitation into methanol. After drying in vacuo, 1.76g (89%) of a white fibrous polymer were collected. The polystyrene equivalent molecular weight (Mw) is 1.3 x 10 by GPC. 

Gel permeation chromatography was carried out at 80 C with 0.05 M lithium bromide in dimethylformamide as eluent on a Waters Associates chromatograph with 10 , 10 , and 50 A i-Styragel columns. The system was equipped with a refractive index detector and was calibrated with narrow distribution polystyrene standards. Results are expressed, therefore, as polystyrene-equivalent molecular weights. 

This means that unavoidable errors result when the calibration made with narrow polystyrene standards is used to characterize polymers of other types. Estimations of Mw obtained with this method are often referred to as polystyrene equivalent molecular weights and their acmal values can be in error by a factor of 2 or 3. 

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