Weight, molecular defined

MWR = is used, where Af is a melt-viscosity-average molecular weight defined by the equation Af = antilog, (0.493 log Tf + 3.5576, where Tj is... 

For some purposes this average may be less useful than the weight average molecular weight defined by which considers the fraction by weight of each molecular size i.e. 

To this end, branching has been determined conventionally in dilute solution by the ratio of intrinsic viscosities of branched and linear polymers having the same molecular weight, defined by (3) ... 

These two types of molecular weight averages are representative of the type called absolute methods, in that well-established thermodynamic equations can be used to convert the experimental data directly into a value of the molecular weight. However, some other methods require calibration. The most important of these indirect methods involves a measurement of the intrinsic viscosity. This quantity is a measure of the extent to which a polymer molecule increases the viscosity of the solvent in which it is dissolved. The viscosity method can be calibrated to yield a viscosity-average molecular weight, defined by... 

Other molecular weights are occasionally used. For example, there is the so-called Z-average molecular weight defined by... 

The number-average molecular weight defined as the total weight of a polymer sample divided by the total number of molecules, is given by... 

The dimensionless quantity relative molecular mass (molecular weight), defined as the average mass of the molecule divided by one twelfth the mass of an atom of the nuclide c, is often used in polymer chemistry and called the molecular weight. In this book, the quantity molar mass is also used and the appropriate SI units are given. 

Fig. 80. Miscibility/composition diagrams for ternary PCL (low molecular weight)/SAN-15/SMA-14 blends at different temperatures, molecular weights defined in text the solid line is a suggested phase boundary separating miscible (larger dots) and immiscible (smaller dots) mixtures taken from [149]...

If two chromatographic peaks are immediately adjacent, their resolution will be unity and the ratio of their molecular weights defined as Under these circumstances, Eq. (3) reduces to... 

The quotient M /M of weight- and number-average molecular wei ts is frequently used as a criterion for the d ee of polydispersity in a sample. This ratio can be looked upon as a relative measure of the spread in molecular weight. Defining the stmidard deviation s of the distribution of the number of molecules over the molecular weights by... 

This definition is attributed to Graessley [52], but it first appears in a paper by Fetters et al. [53]. In order to avoid confusion, in the present book we will reserve the symbol for the entanglement molecular weight defined by Eq. 5.18 and will use for the quantity in Eq. 5.21. The two definitions of the molecidar weight between entanglements are thus given by Eqs. 5.22 and 5.23 ... 

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