Stoichiometric polymerization

Problem 5.31 Stoichiometric polymerization of 1,3,5-benzenetriacetic acid with 1,10-decanediol was conducted beyond the gel point to measure the mass fraction of sol Ws at different extents of reaction p, yielding the following data [22] ... 

A sample of phthalic anhydride which contains 5% (w/w) phthalic acid as impurity is to be polymerized with propylene glycol. What would be the limiting degree of polymerization if stoichiometric polymerization were carried out without taking note of the impurity ... 

There are some cases in homogeneous anionic polymerization in which the initiator dissociates completely with quantitative transformation into the active ionic form and the process is also virually instantaneous (stoichiometric polymerization). This is the case, for example, when one uses, as initiators, alkali organic... 

Problem 5.31 Stoichiometric polymerization of l,3,Sbenzenetriacetic acid with 1,10-decanediol was con-... 

There are some cases in homogeneous anionic polymerization in which the initiator dissociates completely with quantitative transformation into the active ioitic form and the process is also virtually instantaneous stoichiometric polymerization). This is the case, for example, when one uses, as initiators, alkali orgaiuc compounds (e.g., phenyUithium, butylhthium, or sodium naphthalene) in solvents which have unshared electron pairs (Lewis bases). The alkah forms stable positively charged complex ions with the Lewis base (Lenz, 1967), while the organic residue becomes negatively charged (carbanion) and can initiate an ioiuc polymerization [cf. Eqs. (8.11) and (8.12)] ... 

Of course, in reactions (5.A) and (5.B) the hydrocarbon sequences R and R can be the same or different, contain any number of carbon atoms, be linear or cyclic, and so on. Likewise, the general reactions (5.C) and (5.E) certainly involve hydrocarbon sequences between the reactive groups A and B. The notation involved in these latter reactions is particularly convenient, however, and we shall use it extensively in this chapter. It will become clear as we proceed that the stoichiometric proportions of reactive groups-A and B in the above notation—play an important role in determining the characteristics of the polymeric product. Accordingly, we shall confine our discussions for the present to reactions of the type given by (5.E), since equimolar proportions of A and B are assured by the structure of this monomer. 

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. 

We define the problem by assuming the polymerization involves AA and BB monomers and that the B groups are present in excess. We define and to be the numbers of A and B functional groups, respectively. The number of either of these quantities in the initial reaction mixture is indicated by a superscript 0 the numbers at various stages of reaction have no superscript. The stoichiometric imbalance is defined by the ratio r, where... 

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. 

Using the case of f = 3 and p = 0.3 as an example, p, = 0.877 when r = 1 in contrast to, say, 0.886 when r = 0.98. This illustrates that failure to maintain stoichiometric balance continues to have a limiting effect on polymerization in this case also. 

For a fixed extent of reaction, the presence of multifunctional monomers in an equimolar mixture of reactive groups increases the degree of polymerization. Conversely, for the same mixture a lesser extent of reaction is needed to reach a specified with multifunctional reactants than without them. Remember that this entire approach is developed for the case of stoichiometric balance. If the numbers of functional groups are unequal, this effect works in opposition to the multifunctional groups. 

Fig. 13. Polymerization chemistry of phenol—formaldehyde condensation synthesis of novolac resia. The phenol monomer(s) are used ia stoichiometric excess to avoid geUation, although branching iavariably occurs due to the multiple reactive sites on the aromatic ring.

Phosphorus(III) Oxide. Phosphoms(III) oxide [12440-00-5] the anhydride of phosphonic acid, is formed along with by-products such as phosphoms pentoxide and red phosphoms when phosphoms is burned with less than stoichiometric amounts of oxygen (62). Phosphoms(III) oxide is a poisonous, white, wax-like, crystalline material, which has a melting point of 23.8°C and a boiling point of 175.3°C. When added to hot water, phosphoms(III) oxide reacts violentiy and forms phosphine, phosphoric acid, and red phosphoms. Even in cold water, disproportionation maybe observed if the oxide is not well agitated, resulting in the formation of phosphoric acid and yellow or orange poorly defined polymeric lower oxides of phosphoms (LOOP). 

Incorporation of less than a stoichiometric amount of alkyl sulfonamides of copper phthalocyanines into copper phthalocyanine improves the pigment s properties in rotogravure inks (67). Monomeric and polymeric phthalocyanine derivatives with basic substituents adsorb strongly to the pigment surface and promote the adsorption of binder molecules (68—72). 

Foi lineal step-giowth, the numbei-aveiage degree of polymerization, is given by equation 7, where r = j, the stoichiometric ratio of the... 

With as httie as 0.5% hydrolysis of the sulfone monomer, the polymerization stoichiometric balance is sufficientiy upset to prevent high molecular weight polymer from being achieved. The dependence of maximum attainable PSF molecular weight on water content during polymerization can be inferred from Figure 1. 

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

The concept of functionaUty and its relationship to polymer formation was first advanced by Carothers (15). Flory (16) gready expanded the theoretical consideration and mathematical treatment of polycondensation systems. Thus if a dibasic acid and a diol react to form a polyester, assumiag there is no possibihty of other side reactions to compHcate the issue, only linear polymer molecules are formed. When the reactants are present ia stoichiometric amouats, the average degree of polymerization, follows the equatioa ... 

Ah these polymerizations proceed only in the absence of oxygen or water, which react with the highly reactive propagating species. Polymerization is usuahy carried out in an inert, hydrocarbon solvent and under a nitrogen blanket. Under these conditions, polymers with narrow molecular-weight distributions and precise molecular weights can be produced in stoichiometric amounts. 

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