Polystyrene mass range

Figure 1 shows a positive static SIMS spectrum (obtained using a quadrupole) for polyethylene over the mass range 0—200 amu. The data are plotted as secondary ion intensity on a linear y-axis as a function of their chaige-to-mass ratios (amu). This spectrum can be compared to a similar analysis from polystyrene seen in Figure 2. One can note easily the differences in fragmentation patterns between the...

In this stage of the investigation, poly(methyl methacrylates) (PMMAs) were selected as the polymeric probes of intermediate polarity. Polymers of medium broad molar mass distribution and of low tacticity (14) were a gift of Dr. W. Wunderlich of Rohm Co., Darmstadt, Germany. Their molar masses ranged from 1.6 X 10" to 6.13 X 10 g-mol. For some comparative tests, narrow polystyrene standards from Pressure Co. (Pittsburgh, PA) were used. 

MALDI is the method of choice for the analysis of synthetic polymers because it usually provides solely intact and singly charged [62] quasimolecular ions over an essentially unlimited mass range. [22,23] While polar polymers such as poly(methylmethacrylate) (PMMA), [83,120] polyethylene glycol (PEG), [120,121] and others [79,122,123] readily form [M+H] or [M+alkali] ions, nonpolar polymers like polystyrene (PS) [99,100,105,106] or non-functionalized polymers like polyethylene (PE) [102,103] can only be cationized by transition metal ions in their l-t oxidation state. [99,100] The formation of evenly spaced oligomer ion series can also be employed to establish an internal mass calibration of a spectrum. [122]... 

As explained in Sections 16.3.4, 6.4.1, and 16.4.2, SEC is a nonabsolute method, which needs calibration. The most popular calibration materials are narrow molar mass distribution polystyrenes (PS). Their molar mass averages are determined by the classical absolute methods—or by SEC applying either the absolute detection or the previously calibrated equipment. The latter approach may bring about the transfer and even the augmentation of errors. Therefore, it is recommended to apply exclusively the certified well-characterized materials for calibrations. These are often called PS calibration standards and are readily available from numerous companies in the molar mass range from about 600 to over 30,000,000g moL. Their prices are reasonable and on average (much) lower than the cost of other narrow MMD polymers. Other available homopolymer calibration materials include various poly(acrylate)s and poly(methacrylate)s. They are, similar to PS, synthesized by anionic polymerization. Some calibration materials are prepared by the methods of preparative fractionation, for example, poly(isobutylene)s and poly(vinylchloride)s. 

Figure 23 Data of zero-shear viscosities of polystyrene firactions ranging from 900 g.mol l to 30 000 g.mol as a function of temperature [29-37]. The master curve is obtained by experimental shifts from the data of a reference mass of 110 000 g. mole-1, includes more than one hundred experiments lying within the experimental bar error. A least squares analysis gives the parameters of the reference mass and the other ones are deduced fiem the shift frictors.

Figure 15.10 Separation of a polystyrene mixture with a broad molecular mass range [reproduced with permission from R.V. Vivilecchia, B.G. Lightbody, N.Z. Thimot and H.M. Quinn, J. Chromatogr. Sci., 15, 424 (1977)]. Mobile phase, 2mlmin dichloromethane. Molecular masses 1=2145000 2 = 411000 3 = 170 000 4 = 51 000 5 = 20 000 6= 4000 7 = 600 8 = 78 (benzene).

Figure 7.3 Characteristics of stationary phases used for gel filtration and GPC columns. (a) Graphs indicating the mass ranges for two phases in gel filtration and for three phases in gel permeation (b) Calibration curves (logM = /(V)) for these different phases obtained with proteins for gel filtration and with polystyrene standards for the others (known molecular weights). A weak slope from the linear section reveals a better resolution between neighbouring masses. This is the case when the pores are of regular dimension. The curves logM = f[K), more rarely studied, reveal the same aspect (reproduced courtesy of Tosohaas and Polymer Lab.). To avoid protein aggregate formation, denaturing compounds are sometimes introduced to the aqueous mobile phase.

Clearly, the characterization of a broad-MMD calibrant requires a considerable amount of effort and expertise, and they have been mainly used where there are problems in producing narrow-MMD calibrants. In practice, the main applications of this approach have been the use of NBS Standard Sample 706 (polystyrene) and, in particular, NBS Standard Sample 1475 (linear polyethylene). SEC has been a very valuable technique for examining the MMDs of polyethylene, but as there has only been limited success in producing narrow-MMD polyethylene calibrants, NBS 1475 has been widely used for calibrating high-temperature SEC systems used for this application. Unfortunately, the molecular mass range of NBS 1475 is rather low and is not really appropriate for many samples. Barlow et al [5] used NBS 1475 and extended the calibration range with additional polymers (see Chapter 4, section 4.5.1.1). 

Commercial polyethylenes have a broad molecular mass distribution (see Figure 4.2), and a column or columns with a wide range of molecular size separation is required. Polystyrene/divinylbenzene column packings alone have the necessary range and resolution. Silica-based columns may replace these in the future, since they have better thermal stability, but at the moment are limited by the molecular mass range available. 

The following is a summary of the current state of knowledge regarding Dj for polymer solutions. The first observation predates the advent of thermal FFF Dj is independent of polymer molecular mass for a series of linear polystyrene polymers [21,22]. This conclusion has been verified using thermal FFF over a broader molecular-mass range it has also been confirmed in a preliminary manner for polymers such as polymethylmethacrylate and polyisoprene [28]. It has also been found that Dj is the same for linear and branched polymers of the same composition, irrespective of the type of branching [20]. 

Figure 3 Positive ion ToF-SIMS spectrum from polystyrene in the mass range mlz=0-200. (Reproduced with permission from Briggs D (1998) Surface Analysis of Polymers by XPS and Static SIMS. Cambridge Cambridge University Press Cambridge University Press.)...

Aksenov, A.A. and Bier, M.E. (2008) The analysis of polystyrene and polystyrene aggregates into the mega Dalton mass range by cryodetection MALDl TOE MS./. Am. Soc. Mass Spectrom., 19, 219-230. 

Figure 23-10 Purification of carbon nanotubes by molecular exclusion chromatography. An electric arc struck between graphite rods creates nanometer-size carbon products, including tubes with extraordinary strength and possible use in electronic devices. Molecular exclusion chromatography separates nanotubes (fraction i) from other forms of carbon in fractions 2 and 3. The stationary phase is PLgel MIXED-A, a polystyrene-divinylbenzene resin with pore sizes corresponding to a molecular mass range of 2 000 to 40 000 000 Da. Images of carbon in each fraction were made by atomic force microscopy. [B. Zao, H. Hu, S. Niyogi, M. E. Itkis. M. A. Hamon, P. Bhowmik, M. S. Meier, and R. C. Haddon, . Am. Chem. Soc. 2001, i23,11673.]...

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