Big Chemical Encyclopedia

Chemical substances, components, reactions, process design ...

Articles Figures Tables About

Stoichiometric imbalance, effect

We now turn to two of the problems we have sidestepped until now. In this section we consider the polymerization of reactants in which a stoichiometric imbalance exists in the numbers of reactive groups A and B. In the next section we shall consider the effect of monomers with a functionality greater than 2. [Pg.309]

The parameter r continues to measure the ratio of the number of A and B groups the factor 2 enters since the monofunctional reagent has the same effect on the degree of polymerization as a difunctional molecule with two B groups and, hence, is doubly effective compared to the latter. With this modification taken into account, Eq. (5.40) enables us to quantitatively evaluate the effect of stoichiometric imbalance or monofunctional reagents, whether these are intentionally introduced to regulate or whether they arise from impurities or side reactions. [Pg.312]

Eig. 2. Effect of stoichiometric imbalance in polysulfone polymerization on maximum attainable polymer reduced viscosity where (x) is theoretical,... [Pg.462]

In order to properly control the polymer molecular weight, one must precisely adjust the stoichiometric imbalance of the bifunctional monomers or of the monofunctional monomer. If the nonstoichiometry is too large, the polymer molecular weight will be too low. It is therefore important to understand the quantitative effect of the stoichiometric imbalance of reactants on the molecular weight. This is also necessary in order to know the quantitative effect of any reactive impurities that may be present in the reaction mixture either initially or that are formed by undesirable side reactions. Impurities with A or B functional groups may drastically lower the polymer molecular weight unless one can quantitatively take their presence into account. Consider now the various different reactant systems which are employed in step polymerizations ... [Pg.75]

FIGURE 7.1 The effects of conversion and stoichiometric imbalance on the number average degree of polymerization. [Pg.419]

Effectiveness factor is given vs. the intrapellet Damkohler number for different stoichiometric imbalances between reactants A2 and B, denoted by I b, surf-... [Pg.504]

E vs. Aa seems to be most sensitive to product concentrations near the external surface of the catalyst and adsorption/desorption equilibrium constants. I c.surf. I d, surf, and 6>, directly affect the vacant-site fraction on the interior catalytic surface and the rate of reactant consumption. In the previous simulations, product molar densities near the external surface of the catalyst were varied by a factor of 50 (i.e., from 0.1 to 5), and 0, was varied by a factor of 20 (i.e., from 0.05 to 1). The effectiveness factor increases significantly when either 4 c,surf, I d. surf or 6i is larger. E vs. Aa is marginally sensitive to a stoichiometric imbalance between reactants A2 and B, but I B.sur ce was only varied by a factor of 4 (i.e., from 0.5 to 2). A four-fold decrease in the molecular weight of reactant B, which produces two-fold changes in 30b, effective and 5b, does not affect E. [Pg.505]

Another class of adherends is that of thermoplastic polymers. In contrast to metal adherends, thermoplastics are not impenetrable and thus absorption effects can be expected in addition to adsorption phenomena. Hence, given sufficient conditions for preferential absorption, a considerable mass uptake by the thermoplastic can occur, potentially resulting in significant stoichiometric imbalances on the epoxy side. Apart from the driving force for absorption of molecules from the liquid epoxy formulation, it is the diffusivity of these molecules within the thermoplastic which plays a major role in the interdiffusion process. In particular, the diffusivity is affected by the mobility of the host molecules. Thus enhancement of diffusivity occurs in the glass transition region and at higher temperatures when intermolecular cooperative motion is activated. [Pg.118]

To examine the effect of stoichiometric imbalance, consider the limiting case of complete conversion, p= I, for which Equation 8.7 reduces to... [Pg.135]

An alternative procedure would involve feeding the polymerization reactor with a deliberate imbalance of diacid and diamine to limit to 50,000 even if p were effectively forced close to unity. This is not attractive in this particular case because hexamethylene diamine and adipic acid react to form a zwitterion salt (5-5) which can be recrystallized from methanol and used to provide a pure feedstock with a stoichiometric balance of coreactive functional groups. [Pg.173]


See other pages where Stoichiometric imbalance, effect is mentioned: [Pg.461]    [Pg.176]    [Pg.76]    [Pg.461]    [Pg.313]    [Pg.339]    [Pg.252]    [Pg.76]    [Pg.37]    [Pg.290]    [Pg.24]    [Pg.156]    [Pg.228]    [Pg.30]    [Pg.253]    [Pg.309]    [Pg.78]    [Pg.61]    [Pg.41]    [Pg.78]    [Pg.284]    [Pg.465]    [Pg.77]   
See also in sourсe #XX -- [ Pg.252 ]




SEARCH



IMBALANCE

Quantitative Effect of Stoichiometric Imbalance

Stoichiometric imbalance

© 2024 chempedia.info