Molecular weight conversion dependence

Lewis acids 436 metal complex-mediated radical polymerization 484-6 molecular weight distributions 251,453-4, 458-60,490-1.499-501 molecular weight conversion dependence 452-3,455... 

Figure 2. Molecular weight-conversion dependence for VAc polymerization initiated by Al(iBu)3/Bpy/TEMPO (1 1 2). Initiator concentration [I]o. 0.05 M, 60 °C (n) 0.05 M, 20 °C (o) 0.3 M, 60 °C (6). (Reproduced with permission from American Chemical Society)...

Unless working with superdried systems or in the presence of proton traps, adventitious water is always present as a proton source. Polymeriza tion rates, monomer conversions, and to some extent polymer molecular weights are dependent on the amount of protic impurities therefore, weU-estabHshed drying methods should be followed to obtain reproducible results. The importance is not the elimination of the last trace of adventitious water, a heroic task, but to estabhsh a more or less constant level of dryness. 

Optimized molecular weight-conversion relationship is related to the system heat transfer coefficient. The degree of conversion improvement from improved heat transfer depends on the average molecular weights of polymer being produced for a given initiator system. 

Figure 6.24 Molecular weight, M , dependence on monomer conversion for bulk polymerization of styrene at 114°C with only PS-TEMPO adduct initiator (System I) and with both PS-TEMPO and t--butyl hydroperoxide initiators (System n). The theoretical line represents molecular weight calculated on the assumption of a constant number of polymer molecules (due only to PS-TEMPO adduct) throughout the course of poymeriza-tion (Problem 6.42).

Figure C2.1.3. Schematic dependence of tire molecular weight of a polymer as a function of tire degree of monomer conversion for different polymerization reactions.

Prior to the discovery of plentihil suppHes of natural gas, and depending on the definition of the resources (1), there were plans to accommodate any shortfalls in gas supply from soHd fossil fuels and from gaseous resources by the conversion of hydrocarbon (petroleum) Hquids to lower molecular weight gaseous products. 

Bulk polymerization has been studied at relatively low temperatures and in toluene and carbon tetrachloride solutions carried to low conversions (12). The effects of temperature and different organic peroxide initiators have been observed. The molecular weight of soluble polymer after 3% conversion is ca — 19,000 and is somewhat dependent on initiator concentration or temperature between 35 and 65 °C. With di-2-methylpentanoyl... 

The equivalent weight distribution of natural petroleum sulfonates depends on the boiling range of the aromatic components in the feedstock, but generally consists of a broad continuum of molecular weight components (139). For many appHcations it is precisely this property of derived petroleum sulfonates that provides the unique properties, such as emulsification. Conversely, most oil-soluble synthetic sulfonates have much more limited components and molecular weight distribution. 

Although reactivity ratios indicate that VP is the more reactive monomer, reaction conditions such as solvent polarity, initiator type, percent conversion, and molecular weight of the growing radical can alter these ratios (138). Therefore, depending on polymerization conditions, copolymers produced by one manufacturer may not be identical to those of another, especially if the end use appHcation of the resin is sensitive to monomer sequence distribution and MWD. 

For permeation of flavor, aroma, and solvent molecules another metric combination of units is more useful, namely, (kg-m)/(m -sPa). In this unit the permeant quantity has mass units. This is consistent with the common practice of describing these materials. Permeabihty values in these units often carry a cumbersome exponent hence, a modified unit, an MZU (10 ° kgm)/(m -s-Pa), is used herein. The conversion from this permeabihty unit to the preferred unit for small molecules depends on the molecular weight of the permeant. Equation 4 expresses the relationship where MW is the molecular weight of the permeant in daltons (g/mol). 

Factor II. Prothrombin is a vitamin K-dependent compound synthesized by the Hver. When prothrombin is activated it is cleaved at two sites, resulting in a two-chain molecule linked by a disulfide bond that has a molecular weight of 37,000 daltons. Thrombin is the serine protease that initiates the conversion of soluble fibrinogen into fibrin. 

The relative importance of these mechanisms, and the value of the overall kt, depends on the molecular weight and dispersity of the propagating species, the medium and the degree of conversion. The value of k, is not a constant ... 

---