Polyreactions

Deuflhard P and Wulkow M 1989 Computational treatment of polyreaction kinetics by orthogonal polynomials of a discrete variable Impact of Computing in Science and Engineering vol 1... 

S. S. Medvedev, Proc. Int. Symp. Makromol Chem. Prague 1957, Pergamon Press, New York, 1958, p. 174 S. S. Medvedev, YSnet. Mech. Polyreactions, lUPAC Int. Symp. Makromol. Chem., Plenary Main Lect., 1969, p. 39 S. S. Medvedev and co-workers,/ Macromol Sd Chem. Al, 715 (1973). 

Tudcs, f. (Ed.), Kinetics and Mechanisms of Polyreactions, Akademai, Kiado, Budapest (1971)... 

Formation of polymer chains or networks from these compounds can be conceived either as a ring-opening polymerization process or a polyreaction involving exo-cyclic functional groups. 

The problems associated with route B also have something to do with steric hindrance. Here the critical point is the steric demand of both monomer and chain end. Incoming monomer will only be connected to the chain end, if steric hindrance is not too high. Otherwise this process will be slowed down or even rendered impossible. Depending on the kind of polyreaction applied, this may lead to termination of the reactive chain end and/or to side reactions of the monomer, like loss of coupling functionality as in some polycondensations or auto-initiation specifically in radical polymerizations. From this discussion it can be extracted that the basic problems for both routes are incomplete coverage (route A) and low molecular weight dendronized polymer (route B). 

For a crosslinking polyreaction the functionality of the monomers is the basic parameter. However, it was found long ago that, after their reaction, not all functional groups are involved in intermolecular crosslinks but also in intramolecular and cyclic links. 

In monolayers the polyreaction is only possible, if the monomers are in the condensed phase. (That this, however, is some-... 

In-all. cases the polyreaction at a constant surface pressure can qualftatively be followed by the change of surface area (32). 

Although monolayers at the gas-water interface are useful to study adsorption phenomena of e.g. proteins at membranes they are not a very good model, since they represent only one half of a biological membrane. Attempts have therefore been made to extend this concept of polymer monolayers to bilayers and particularly to liposomes. It was to prove, whether the monomers (Table I.) could form bilayers and whether a polyreaction within these bi-layers was possible under retention of the structure and the orientation of the molecules. 

Polymerization in Bilayers. Upon irradiation with UV light the monomer vesicles are transferred to polymer vesicles (Figure 12.). In the case of the diyne monomers (2,5-9,12,13,14) the polyreaction can again be followed by the color change via blue to red except phospholipids (5,6), which turn red without going through the blue intermediate as observed in monolayers. The VIS spectra of these polymer vesicle dispersions are qualitatively identical to those of the polymer monolayers (Figure 13.). 

The basic characteristics as well as some advantages and disadvantages are illustrated in Sects. 2.2.2 (polyreactions in bulk), 2.2.3 (polyreactions in solution), and 2.2.4 (polyreactions in dispersion). Prior to this some special features... 

Polyreactions in bulk are divided into homogeneous and heterogeneous reactions, depending on whether the polymer remains dissolved in its monomer or not or, respectively, whether the polyreaction is performed above or below the softening temperature of the polymer. 

In heterogeneous polymerizations in bulk, the formed polymer is insoluble in its monomer and the polyreaction is performed below the softening point of the polymer. On an industrial scale, this type of process is especially utilized for chain polymerizations, for example, the radical polymerization of liquid vinyl chloride, the polymerization of liquid propylene with Ziegler-Natta or with metallocene catalysts, and the polymerization of molten trioxane. 

Besides in the liquid phase, some polyreactions are also performed in the solid state, for example, the polymerization of acrylamide or trioxane (see Example 3-24). The so-called post condensation, for example, in the case of polyesters (see Example 4-3), also proceeds in the solid phase. Finally, ring closure reactions on polymers with reactive heterocyclic rings in the main chain (e.g., poly-imides, see Example 4-20) are also performed in the solid state. 

There are two different ways for carrying out polyreactions in a solvent. When both the monomer and the resulting polymer are soluble in the solvent, one speaks of a homogeneous solution polymerization on the other hand, if the polymer precipitates during the course of the reaction, it is called precipitation polymerization. By addition of a solvent, different effects are obtained Basically, the viscosity of the reaction mixture is decreased in comparison to a bulk polyreaction this facilitates heat transfer, mass transport, and handling. 

It was not until the synthesis was accomplished in two steps that it became possible to process these polymers from solution. In the first reaction step, two tetrafunctional monomers form a linear and soluble macromolecule by a polyreaction of two of the functional groups of each molecule. Subsequently, cy-... 

Stepwise addition polymerisation (polyaddition) or condensation polymerisation (polycondensation) are possible polyreactions for the first step. The two latter combinations attained interest in the technical synthesis of polyimides and polybenzimidazoles. 

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