Molecular weight. See

They are colourless liquids with characteristic odours, and are prepared by the condensation of ketones with alkyl orthoformates in the presence of alcohols, or by the reaction of acetylenes with alcohols in presence of HgO and BF3. In some cases trichloroethanoic acid is used as the catalyst. They lose alcohol when heated and form vinyl ethers. Exchange of alcohol groups occurs when the ketals of the lower alcohols are boiled with alcohols of greater molecular weight. See acetals. 

Even lower molecular weights will be obtained where there is an excess of one reactive group, since these will eventually monopolise all the chain ends and prevent further reaction. The presence of monofunctional ingredients will have similar effects and they are sometimes added deliberately to control molecular weight (see for example Section 20.4.1). 

The properties of styrenic block copolymers are dependent on many factors besides the polymerization process. The styrene end block is typically atactic. Atactic polystyrene has a molecular weight between entanglements (Me) of about 18,000 g/mol. The typical end block molecular weight of styrenic block copolymers is less than Mg. Thus the softening point of these polymers is less than that of pure polystyrene. In fact many of the raw materials in hot melts are in the oligomeric region, where properties still depend on molecular weight (see Fig. 1). 

The refining of oil produces the monomer feed streams for tackifiers as byproducts of the process. Tackifiers are low molecular weight polymers, typically 300-5000 g/mol, most often 500-1000 g/mol. Generally molecular weights are well below Mg and thus, within a given class of resins, softening points are controlled primarily by molecular weight (see Fig. 1). 

The composition of the nonsolvent-solvent mixture representing the critical composition of the ternary system with polymer of infinite molecular weight (see Fig. 123,a) possesses unique significance. Scott and Tompa have shown that the composition at the critical point in the limit of infinite molecular weight is specified by... 

Several other synthetic techniques have also been described. Redistribution polymerization was outlined in COMC II (1995) (chapter Organopolysilanes, p 99) and proceeds by phosphonium salt-catalyzed redistribution of chlorodisilanes.133 Disproportionation polymerization, which is a similar process, has been described for the formation of polymers by ethoxide-catalyzed disproportionation of alkoxydisilanes via silyl anion intermediates.134 These procedures give rise to network polymeric products of rather low molecular weight (see below, Section 3.11.7.1). 

The stiffness of the main chain of a polymer is of great importance for the solution viscosity the stiffer the chain is, the higher is the viscosity for polymers with the same molecular weight (see Sect. 2.3.3.3.1 for the dependency of K and a in the viscosity equation on the shape of macromolecules in solution). 

In zinc-deficient rats, the zinc content of the epididymis was only about half the normal value,28,87 and the level of a-D-mannosidase activity was also little over half the value usually observed.26 However, the zinc concentration of the tissue was still in vast excess over that required for stoichiometric combination with the enzyme protein, calculated on any probable estimate of its specific activity and molecular weight (see Section III,5 p. 433). 

Appropriate column set suitable for the analysis of high molecular weight (see Notes 1 and 2)... 

JComparable data for phytochrome preparations of the same molecular weight (see Tables 1, 3, and 4 and the text) may show small deviations, which are insignificant considering the fact that these values have often been measured at different times with samples obtained from different isolation runs. 

Visualize protein bands by Coomassie brilliant blue (see Support Protocol 1) or silver staining (see Support Protocol 2). To estimate protein molecular weight, see Support Protocol 3. 

Fig. 11a,b. Bright field TEM micrographs of a a linear tetrablock copolymer b a topologically asymmetric miktoarm starblock copolymer of the same composition and molecular weight (see text) (reproduced with permission from [62])... 

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