Molecular weight determination poly

The phenomena we discuss, phase separation and osmotic pressure, are developed with particular attention to their applications in polymer characterization. Phase separation can be used to fractionate poly disperse polymer specimens into samples in which the molecular weight distribution is more narrow. Osmostic pressure experiments can be used to provide absolute values for the number average molecular weight of a polymer. Alternative methods for both fractionation and molecular weight determination exist, but the methods discussed in this chapter occupy a place of prominence among the alternatives, both historically and in contemporary practice. 

Molecular weight determinations of ECH—EO, ECH—AGE, ECH—EO—AGE, ECH—PO—AGE, and PO—AGE have not been reported. Some solution studies have been done on poly(propylene oxide), and these may approximate solution behavior of the PO—AGE copolymer (33,34). 

Devaux, J., Delimoy, D., Daoust, D., Legras, R., and Mercier, F. J., On the molecular weight determination of a poly(aryl-ether-ether-ketone) (PEEK ), Polymer, 26, 1994, 1985. 

Poly-(iV-/3-hydroxyethyl-2,2,6,6-tetramethyl-4-hyd-roxypiperidyl succinate) (II) (Figure 4.15) is an oligomer where n is assumed to be 2-14, whereas the majority of the product is believed to be n = 11-14. The average molecular weight, determined by SEC,... 

MOLECULAR WEIGHT DETERMINATION OF POLY(DIMETHYL SILOXANE) COPOLYMERS VIA GEL PERMEATION CHROMATOGRAPHY... 

Staudinger was probably the first to recognize this, for in 1928 he proposed that synthetic macromolecules were poly-disperse and their molecular weights would have to be expressed as average values (93). He also recognized the dependence of physical properties on molecular weight, and pursued this dependence as a measure of molecular weight determination. The result was his application of solution viscosity. 

Table 1. Molecular weight determination for poly(4-methyl-l-pentene)...

Many natural polymers are monodisperse (all molecules have the same molecular weight). In this case the ullracentrifuge which separates materials according to their effective density in solutions is a most powerful tool for molecular weight determination. With poly-disperse materials, the interpretation of ultracentrifuge results becomes more complex and widespread application of this method to synthetic polymer molecular weighl determination has not yet been achieved... 

The poly(metal)silazanes 62-77 are isolated usually as colorless crystals. They are unstable with respect to water and oxygen and are soluble in nonpolar solvents (with the exception of compound 77), The formulas drawn for 64-67 are merely formal and do not imply that these substances have a considerable ionic character. They are soluble in benzene and are monomo-lecular as found by cryoscopic molecular weight determinations. The H NMR spectra of 64 and 65 (64) demonstrate that the metal atoms are coordinated by methyl groups, the most reasonable structure being depicted in the formulas 64 and 65. The trigonal-bipyramidal arrangement of the N2SiAlM... 

Similar work was performed by Asami on the copolymerization of poly-THF macromonomers The formation of graft copolymers was evidenced though their molecular weights, determined by GPC, were obviously underestimated. 

C 25 Co nix, A. On the molecular weight determination of poly (ethylene terephtha-late). Makromol. Chem. 26, 226 (1958). 

Research grade poly(styrene-b-butadiene-b-styrene), designated as TR-41-1647, TR-41-1648, and TR-41-1649, were received from Shell Development Co. These block copolymers contain 26.8, 29.3, and 48.2 wt% polystyrene (PS), respectively. The average molecular weights, determined by intrinsic viscosity measurements in toluene at 30°C, were found to be 7-36-6, 16-78-16, and 14-30-14 in units of thousands. The microstructure of polybutadiene (PB) blocks was found to contain about 40 mol% in cis-1,4, 50% in trans-1,4, and 10% in 1,2 units. 

The molecular weight-mobility relations shown in Fig. 7.18 indicate that all RNA species do indeed behave as homologues in formamide. Most strikingly, poly(rA) and poly(rU) fractions conform to the same law. Two-stranded viral RNAs do not necessarily melt spontaneously at room temperature, but remain in the fully melted state after heating to 40 or 50°C (Finder et al. 1974a). The formamide method has been successfully used for molecular-weight determination of such species (Bevan et al. 1973). 

Three histone-specific acetyltransferases have been partially purified and characterized from rat thymus nuclei (225). The enzymes were extracted from rat thymus nuclei by sonication in the presence of 1M ammonium sulfate and separated into two active fractions (A and B) by DEAE-cellulose chromatography. Fraction B was further separated into two active fractions (Bi and B2) by gel filtration on Sephadex G-200. Each fraction was then purified further by chromatography on hydroxyapatite. The molecular weights, determined by Sephadex G-200 and by sucrose density gradient centrifugation, were 99,000, 110,000, and 92,000 for enzymes A, Bi, and B2, respectively. All three enzymes required acetyl CoA as acetate donor, and the activity of the enzymes was inhibited by p-chloromercuribenzoate. Acetyltransferase A preferentially acetylated histone I (FI) and also poly-L-lysine. Acetyltransferase Bi and B2 preferred histone H4 (other names IV, F2al) and did not acet-ylate poly-L-lysine and histone H3 (III, F3). In addition to c-N-acetyl-lysine, two other unidentified amino acid derivatives were obtained from a digest of histone H4 acetylated by the two B enzymes. 

The molecular weight obtained by application of Eq. (4.82) to a poly disperse polymer will be some average over the molecular weight distribution characteristic of the polymer. It can be easily shown that the molecular weight determined from light scattering measurement is Mw (see Problem 4.13). 

Materials. Three samples of poly-7-benzyl-L-glutamate were studied. Polymer I was obtained by polymerizing 7-benzyl A-carboxy-L-glutamate anhydride by sodium methoxide in DMF and polymer II by a similar polymerization using n-hexylamine as initiator. Both were purified by reprecipitation. The molecular weights determined from the viscosity-molecular weight ratio of Doty et al. (4) were 67,000 for polymer I and 21,000 for polymer II. Polymer III was a commercial sample (Pilot Chemical Co.) of molecular weight 275,000. All solvents were purified by standard laboratory procedures. 

Calculate the number average, weight average from these data. Draw the molecular weight distribution curve and indicate in the plot the position of the weight- and number-average molecular weights. Determine the poly-dispersity of the sample. 

Theoretical and experimentally determined volume fraction of PLA Total molecular weight determined by NMR and poly(styrene) calibrated SEC Total degree of polymerization calculated using the NMR data... 

Ohtani, H., Tanaka, M., and Tsuge, S., End Group of Poly(methyl methacrylate) as a Fimction of Molecular Weight Determined by Pyrolysis-Gas Chromatography, Bull Chem. Soc. Japan, 63,1196, 1990. 

Recently, Ballard and co-workers discovered a novel path to prepare linear polyphenylene, based on the polymerization of derivatives of 5,6-dihydroxycyclohexa-1,3-diene. The advantage of this method is that the diene polymer remains soluble in a variety of solvents, because of the presence of solubilizing groups, such as ester functions. Because of this, molecular weight determinations can be made before the final pyrolysis to remove the attached groups. Ballard et al. reported that the final product is a high molecular weight poly(p-phenylene). 

---