Polycondensation multifunctional

Scheme 6. The multifunctional polycondensation synthetic strategy to polycatenane.

The principle of the second synthetic approach to polycatenanes, i.e. stepwise polycondensation, has been proposed by Shaffer and Tsay, but not experimentally demonstrated [42, 43], This approach has the advantage over multifunctional polycondensation that a linear polymer is formed before cyclization (Scheme 7). However, the second step, which consists of the cyclization of n macrocycles along the polymer chain 19, is likely, again, to give rise to an undefined network, containing some rotaxane and catenane units 21, similar to the multifunctional polycondensation approach. 

Figure 16 represents schematically a vatiation of molecular mass and content of sol fraction, calculated on the basis of the branching the ory, in the process of three-dimensional polycondensation of multifunctional compounds [89, W]. According to these calculations, the weight-average molecular mass of curing oligomer increases monotonically up to the gel point where it diverges. At this same point the gel appears. A real variation of the same characteristics, obtained on the basis of GPC analysis of curing of an epoxy resing with diamine and dibutylphthalate has a different nature (Fig. 17). Molecular mass of the resulting...

Nevertheless, the route is attractive, because many interesting ladder structures are not accessible using the polycondensation or polyaddition of multifunctional monomers [2, 5]. Besides the specific problems of ladder polymer synthesis discussed above, another problem is almost invariably associated with... 

Polycondensation Methods of Preparing Ladder Polymers (Multifunctional Condensation)... 

The authors feel, that the classification of the synthetic principles applied here is somewhat arbitrary. Multifunctional polycondensations which are conducted in a two-step manner (generation of single-strand intermediates, followed by cyclization), could be classified with the same justification as stepwise processes. On the other hand some of the stepwise syntheses of ladder structures constitute condensations of multifunctional monomers (e.g. the use of butadiynes as starting compounds, see Sect. 4.1.). 

A new quality in ladder polymer synthesis via multifunctional polycondensation was reached in the late 1960s when poly(benzimidazobenzo-phenanthroline) (BBL) 12 was prepared by Arnold and van Deusen [21 -24]. The polymer was synthesized from naphthalene-l,4,5,8-tetracarboxylic acid dianhydride (11) and 1,2,4,5-tetraaminobenzene (la) in strong acidic media (polyphosphoric acid, sulfuric acid). BBL is completely soluble in concentratal sulfuric acid or methanesulfonic add and is processible into durable films and... 

The majority of ladder polymem, however, synthesized by multifunctional polycondensation do not have a well-defined structure, sinre side reactions such... 

Case 3 Case of Many Mono-, Bi-, Tri-, and Multifunctional Monomers The equations described in the previous two cases are not applicable to polycondensation systems in which either monofunctional monomers are present or a great number of branching monomers of a number of different functionalities of both type A and B are present. If one considers the most general case of a polycondensation system as... 

In interfacial polymerization, the two reactants in a polycondensation meet at an interface and react rapidly. The substances used are multifunctional monomers. Generally used monomers include multifunctional isocyanates and multifunctional acid chlorides. The basis of this method is the classical Schottenn-Baumann reaction between an acid chloride and a compound containing an active hydrogen atom, such as an amine or alcohol, polyesters, polyurea, and polyurethane. Under the right conditions, thin, flexible waUs/sheU will be formed at or on the surface of the droplet or particle by polymerization of the reactive monomers. 

Let s now talk briefly about branched polymers. If, say, polycondensation is going on, and initial monomers have only two functional groups each, then we shall end up with linear polymer chains (with a small proportion of loops). However, if the monomers have three or more functional groups, a branched macromolecule can be synthesized (see Figure 2.8 c). Given plenty of multifunctional monomer units at the start, one can even obtain a polymer network (Figure 2.8 d). 

Descriptions of networks in terms of cross-link index and density provide no information on the internal architecture, that is, the homogeneity, of the network. Depending on how they are produced, most networks are more or less inhomogeneous, that is, the local density has a distribution. With multifunctional polycondensation, the gel point is most often reached at relatively high yields, and the network formed is quite homogeneous. In addition polymerization, the gel point occurs already at relatively low yields. The polymerization continues around the spatially fixed network structured centers, and, so, densely cross-linked centers are produced within a less densely cross-linked matrix. 

Since the monomers are joined by ester linkages, the resulting polymer is called polyester. The polycondensation can be achieved in melt, solution, and at interfacial boundary between two liquids in which the respective monomers are dissolved. It is a slow step addition process and molecular weight is >1,00,000 and highly dependent on monomer stoichiometry. The addition of little amount of tri- or multifunctional monomers develops extensive cross-linking. 

With multifunctional polycondensations, however, the yield of reacted functional groups does not have to be very high to produce cross-linked polymers. In this case, it only requires at least two functional groups per initially present chain to react before they are all cross-linked to each other (Section 17-5). Thus, the requirement of high yield for high degrees of polymerization is not so critical in the case of multifunctional polycondensations as it is for bifunctional polycondensations. 

Under certain conditions, however, multifunctional polycondensations produce linear or branched polymers instead of cross-linked networks. If the functional groups are favorably arranged spatially, of course, cyclization reactions occur instead of cross-linking reactions. Such cyclopolycondensations are especially important for producing polymers with hetero rings in the main chain. 

At least one reaction partner has a functionality of three or more in multifunctional polycondensations. In certain cases, two of the groups of a trifunctional molecule can react with a group from a bifunctional molecule to form a ring. Thus, in such cyclopolycondensations, linear or slightly branched polymers are produced despite there being a multifunctional molecule present at the start of the polycondensation. But in all other multifunctional polycondensations a network polymer is obtained above a certain conversion which is macroscopically manifested as the gel point of the system. 

According to this equation, the extent of the reaction (pA)cnt at the gel point depends only on the functionality / of the branch molecules, the molar fraction xk of the branch molecules, and the ratio ro of functional groups. These predictions are confirmed by experiment, since gel formation in the polycondensation of 2 mol of glycerine with 3 mol of phthalic anhydride (ro = 3 2/2 3) andxA = 1 always occurs at the same degree of reactionpA (Table 17-8). The gel point occurs at higher yields, however, than is calculated [theoretically (pA)cnt = 0.707]. Similar effects have also been observed with other multifunctional polycondensations (Table 17-9). 

Figure 17-9. Variation with time of the viscosity v (in 0.1 Pa s), the number-average degree of polymerization the extent of reaction p, and the branching coefficient in the p-toluene sulfonic-acid-catalyzed multifunctional polycondensation of diethylene glycol with a mixture of succinic acid and tricarballylic acid, ro = 1.002 xa = 0.404at 109° C gel = gel point. (After P. J. Flory.)...

In this approach, AB2 type or other similar monomers such as AB (x = 4, 6, 8, etc.) monomers are polymerised by a polycondensation reaction. Gelation, a general problem in the polymerisation of multifunctional monomers, is avoided by the use of a dilute solution and the slow addition of monomer(s). Vegetable oil-based hyperbranched polyhydrocarbons, polyethers, polyesters, polyamides, and so on may be prepared by this method. 

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