Average Molecular Weight Values

Small molecules, such as benzene and glucose, have precise structures, such that each molecule of benzene has six carbon atoms and six hydrogen atoms. By comparison. 

Nitro-/j-octane 7.0 Diisobutyl ketone 7.8 Isoamyl alcohol 10.0 

Carbon tetrachloride 8.6 Methyl ethyl ketone 9.3 n-Amyl alcohol 10.9 

While there are several statistically described averages, we will concentrate on the two that are most germane to polymers—number average and weight average. These are averages based on statistical approaches that can be described mathematically and that correspond to measurements of specific values. 

Polymer Hydrogen Bonding Hydrogen Bonding Hydrogen Bonding 

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The objective of this present work was to investigate the feasibility of using GPC/DV for absolute molecular weight determination of hydroxypropylated lignins. In order to verify the validity of the universal calibration method, vapor phase osmometry (VPO) was used to provide reference number average molecular weight values. Comparisons with LALLS results have also been made and will be reported in another publication. 

Table 27.3 Fractions of aromatic hydrocarbons and averaged molecular weight values measured by field desorption mass spectrometry (FD-MS) analysis on the crude and C-grade oils...

Chitinase from Bacillus sp. was added to a solution of Xyl (l— 4)GlcNAc oxazoline 13 dissolved into a phosphate buffer. The consumption rate of 13 was accelerated by the enzyme addition and chitin-xylan hybrid polysaccharide 14 was produced. During the polymerization, the reaction proceeded homogenously throughout the reaction. The yield was 76% and its average molecular weight value of 14 was M = 1500 with MJMa = 1.76, determined by GPC. Furthermore, MALDI-TOF mass spectrum of 14 indicated the peaks at every m/z 335, which corresponds to the molecular mass of the repeating disaccharide unit. 

All polymers usually contain molecules of varying molecular weight. The manufacturer commonly lists the average molecular weight value. The size of sodium hyaluronate set for production varies. Amvisc , for example, is formulated to a molecular weight of 2 million Daltons, a dynamic viscosity of 40 000 mPas at 25 C and a shear rate of 2 per second. Healon , in contrast, is formulated to a concentration of 10 mg/ml (compare to information leaflet). 

It can be seen that combining different techniques makes the determination of M and and hence PI, possible. A value of PI close to 1 indicates a very narrow distribution of the chain length around the average molecular weight values calculated from the distribution curve, while a PI value much larger than 1 indicates a wide distribution of the molecular weight of the polymer chains contained in the population. 

Average molecular weight values of the original and recovered A-grade heavy oil measured by FI-MS and GPC with different detectors... 

Average molecular weight values measured by FD-MS analysis and fractions of aromatic hydrocarbons in original and recovered crude oil and C-grade heavy oil... 

Combined measurements by GPC and LS of fractionated poly(methylphenyl)silane were performed in THF. They indicate that the absolute weight average molecular weight values of PSi do not differ largely from the GPC values previously obtained using a classical GPC calibration with monodisperse PS standards. Nevertheless, two calibration procedure were developped from which one allows to get free from polysilane "standards". 

Typical number = average molecular weight values, as measured by VPO or GPC, are between 5,000 and 20,000 (n = 7-25). Thus in many cases, the polymers are best described as oligomers. However, it is important to note that no effort was made to maximize the molecular weights. 

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