molecular weight

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weight

 [wāt]
1. heaviness; the degree to which a body is drawn toward the earth by gravity. (See also Tables of Weights and Measures in the Appendix.) Abbreviated wt.
2. in statistics, the process of assigning greater importance to some observations than to others, or a mathematical factor used to apply such a process.
apothecaries' weight see apothecaries' system.
atomic weight the sum of the masses of the constituents of an atom, expressed in atomic mass units (or daltons), in SI units (i.e., kilograms), or as a dimensionless ratio derived by comparing the mass to the mass of an atom of carbon-12, which is taken as 12.000. Abbreviated At wt.
avoirdupois weight see avoirdupois system.
equivalent weight the amount of substance that combines with or displaces 8.0 g of oxygen (or 1.008 g of hydrogen), usually expressed in grams; for acid/base reactions, one equivalent donates or receives a mole of protons and the equivalent weight is the ratio of the molecular weight to the number of protons involved in the reaction. For oxidation-reduction reactions, one equivalent donates or receives a mole of electrons and the equivalent weight is the ratio of the molecular weight to the number of electrons involved in the reaction.
gram molecular weight the molecular weight of a substance expressed in grams; one gram molecular weight of a molecular substance contains one mole of molecules. See also mole1.
low birth weight (LBW) see under infant.
molecular weight the weight of a molecule of a chemical compound as compared with the weight of an atom of carbon-12; it is equal to the sum of the weights of its constituent atoms and is dimensionless. Abbreviated Mol wt or MW. Although widely used, the term is not technically correct; relative molecular mass is preferable.
very low birth weight (VLBW) see under infant.

mo·lec·u·lar weight (mol wt, MW),

the sum of the atomic weights of all the atoms constituting a molecule; the mass of a molecule relative to the mass of a standard atom, now 12C (taken as 12.000). Relative molecular mass (Mr) is the mass relative to the dalton and has no units.
See also: atomic weight.

mo·lec·u·lar weight

(mŏ-lekyū-lăr wāt)
The sum of the atomic weights of all the atoms constituting a molecule; the mass of a molecule relative to the mass of a standard atom, now 12C (taken as 12.000). Relative molecular mass (Mr) is the mass relative to the dalton and has no units.
See also: atomic weight
Synonym(s): molecular weight ratio, relative molecular mass.

molecular weight

The sum of the weights of all the atoms in the molecule.

mo·lec·u·lar weight

(mol wt, MW) (mŏ-lekyū-lăr wāt)
The sum of the atomic weights of all the atoms constituting a molecule.
Synonym(s): molecular weight ratio, relative molecular mass.
References in periodicals archive ?
Two narrow polystyrene standards (obtained from Pressure Chemicals) with weight-average molecular weight ([M.sub.w]) of 30 and 200 kD, respectively, were used for the normalization of light scattering signals and determination of interdetector delay volume and band broadening.
The weight-average molecular weight ([M.sub.w]) and polydispersity index (PDI) are determined with the light scattering detector.
The weight-average molecular weight ([M.sub.w]) and polydispersity index (PDI) data calculated from the light scattering signals are summarized in Table 1.
Their results suggest that weight-average molecular weight, molecular weight distribution, and presence of tie molecules between lamellae all contribute to the increase of [K.sub.Ic], with the weight-average molecular weight being the most important parameter for the fracture behavior.
For polyethylene of similar concentration in short branches, their study shows that the increase of the weight-average molecular weight from 176,600 to 232,900 causes a significant increase of [K.sub.Ic]] from 1.4 to 1.9 MN.[m.sup.[-3/2]].
Similarly, the fracture toughness can be enhanced by the resistance to crack growth because of the presence of tie molecules, even though the tensile yield strength, thus the weight-average molecular weight, is relatively low.
For the C8 copolymers, the [w.sub.e] values based on [W.sub.D] suggest that their toughness is dominated by the weight-average molecular weight, possibly because these copolymers have a relatively low molecular weight, thus very few of the classical type of tie molecules exist in the interlamellar amorphous regions.
Figure 10 shows the zero-shear viscosity data of all CRPP samples at three test temperatures as a function of weight-average molecular weight. The data points at an individual test temperature can be fitted linearly despite the scatter in the data.
To illustrate this effect, elongation at break for all process settings over the weight-average molecular weight [M.sub.w] calculated from the viscosity number data is shown in Fig.
Table 1 includes the number-and weight-average molecular weights of the four polymers.