Nonactivated Polymerization

The Ullman reaction has long been known as a method for the synthesis of aromatic ethers by the reaction of a phenol with an aromatic halide in the presence of a copper compound as a catalyst. It is a variation on the nucleophilic substitution reaction since a phenolic salt reacts with the halide. Nonactivated aromatic halides can be used in the synthesis of poly(arylene edier)s, dius providing a way of obtaining structures not available by the conventional nucleophilic route. The ease of halogen displacement was found to be the reverse of that observed for activated nucleophilic substitution reaction, that is, I > Br > Cl F. The polymerizations are conducted in benzophenone with a cuprous chloride-pyridine complex as a catalyst. Bromine compounds are the favored reactants.53,124 127 Poly(arylene ether)s have been prepared by Ullman coupling of bisphenols and... 

A2 is also a known function of T and space velocity since the rate constant K2 is known from the steady state results (eq. 1). The parameters Ai and Af are not known independently however, the ratio Aj/Af equals the adsorption coefficient Kpr of propylene oxide which is a known function of T obtained from the steady state measurements (eq. 1). Since the steady state kinetics indicate that the surface reaction is the rate limiting step it can be concluded that Ai is larger than A2. It was assumed that propylene oxide adsorption is nonactivated and Aj was arbitrarily set equal to be two times larger than A2 at 400°C,for Y =. 002 then Aj was calculated from Af = Ai/Kpro Yp. The numerical simulations indicated that the model predictions are rather insensitive to Aj but are sensitive to the unknown parameters A3 and 0 c Since the Heat of Polymerization of Propylene Oxide is 18 Kcal/mol the parameter 0 was set equal to 0 exp(-18000/RT). 

It has long been known that polymerization of nonactivated organic compounds occurs in the solid crystalline state, but the systematic and scientific study of this phenomenon was only begun a few years ago. 

The sublimation of jfjhosphorus with and without the aid of discharge plasma is schematically shown in Fig. 39, together with the various solid polyforms and the conditions for their mutual transformations The thermodynamically stable black phosphorus as well as the slightly metastable red phosphorus evaporate associatively with formation of tetrahedral P4 molecules. Upon nonactivated condensation these molecules remain preserved and the metastable, white phosphorus is deposited. Thus, both the evaporation as well as the condensation of red and black phosphorus is kinetically hindered. The effect of the discharge maintained in the phosphorus vapor is to dissociate these valence saturated P4 molecules, which facilitates conditions for the formation of the polymeric red phosphorus. By means of chemical transport even the stable, orthorhombic modification, amorphous as well as polycrystalline has been obtained... 

Polymerizations in the presence of acylating agents are often called activated polymerization. If the acylating agents are absent from the reaction mixture, the reactions may be called nonactivated. Sometimes, the terms assisted and nonassisted are used instead. 

Among other polymer-bound catalysts, onium compounds can be used successfully in halogen exchange reactions between activated and nonactivated halides. This is the case, for instance, in additions to the double bonds of dichlorocarbene to form substituted cyclopropanes and in C-alkylating nitriles. When optically active polymeric ammonium compounds are used as catalysts in carbene addition reaction, chiral products form. ... 

It should be borne in mind that each activated monomer and polymer should only react with nonactivated monomer (addition polymerization) in both of these chemical examples. Reaction between an activated monomer and another activated monomer or a polymer (polycondensation) should not occur. With cyclophane, the mathematical treatment of the consecutive equilibria yields different expressions to those given in Table 16-1, since the /7-cyclophane, as initial monomer unit, yields two activated monomer molecules, and each reaction with activated monomer and its successive products yields only species with uneven numbers of structural elements. In addition, the polymerization of p-cyclophane is no longer a living polymerization when the degrees of polymerization are low, since, in this case, monomolecular (that is, intramolecular) termination reactions leading to the formation of inactive rings can occur. 

III. The polymerization takes place without the intervention of any intermediate state in equilibrium with the nonactivated species, and without any initiator participation ... 

Lipase-Catalyzed Polymerization of Dicarboxylic Acids or Their Derivatives. Enzymatic synthesis has been achieved via various combinations of dicarboxylic acid derivatives and glycols. As to the diacid monomer, dicarboxylic acids, activated and nonactivated esters, cyclic acid anhydrides, and polyanhydrides were enzymatically reacted with glycols under mild reaction conditions. 

Significantly low is the so-called ceiling temperature of the six-membered 2-piperidone (Tc = 60°C). Equilibrium monomer concentration can be obtained by analyzing the equilibrated polymer, but reliable [Mje data are effectively accessible only in a few cases. For instance, the polymerization of 2-pyrrolidone cannot be regarded as an equilibrium reaction due to the irreversible crystallization during polymerization thus, only a so-called limiting polymerization temperature has been kinetically extrapolated by experimental data. By this way, the actual temperature limit has been found to depend upon the type of initiation, being 66 ° C for its nonactivated anionic polymerization and 76 °C for the activated anionic pol)unerization. ... 

The nature and concentration of the initiator play a cmcial role in the nonactivated anionic polymerization, where the growing centers are formed in the slow reaction [46] between the monomer and the lactam anion bringing about the presence of some induction periods. On the other hand, the evaluation of the specific action of a given initiator in the activated lactam polymerization is more complex, since it cannot be taken in consideration apart from the activator used. It is necessary to consider here the dual system initiator/activator. It seems that the activation energy for the anionic ring-opening polymerization of CL is almost independent of the activator used, " whilst it is probably a fimction of the initiator nature. 

The use of strong bases alone is a limiting factor in the anionic lactam polymerization since high polymerization temperatures and relatively slow reaction rates are necessarily implied side reactions are, therefore, unavoidable. Moreover, only the more reactive lactams, such as CL and ((-enantholactam, readily polymerize in nonactivated reaction conditions. The less reactive lactams, such as 2-pyrrolidone and 2-piperidone, are much harder to polymerize because the formation of the imide dimer is more difficult. These limitations can be overcome if the imide is generated by reaction of... 

Indeed, apart from some specific effects linked to the different nature of R substituents in the acylated lactam, reaction [83] is the same as reaction [49] consequently, the artivator addition allows to avoid the slow self-initiation step, obtaining immediately the fast propagation reaction. In other words, the initiation of activated polymerization corresponds to the fast propagation step in the nonactivated lactam polymerization. 

The anionic polymerization of 2-pyrrolidone has also been accomplished employing carbon dioxide as activator. The use of this gaseous activator has made possible to prepare a PA4 possessing a satisfactory thermal stability for fiber preparation and melt spinning. Nonactivated anionic polymerization, on the contrary, enables high molar masses of poly (2-pyrrolidone) to be obtained, but at the expenses of much longer polymerization times. 

Formation of the nonionic growth center (N-acylated lactam) is the controlling step of the polymerization process. Thus, the nonactivated (nonassisted) [7] polymerization, in which the initiation system consists solely of the lactam anion, has an autocatalytic character [12]. 

During the nonactivated polymerization, the nonionic growth centers are formed continuously through a slow reaction between the lactam and its anion (see Equation 7.2), and their concentration is at least one order of magnitude lower than the initial concentration of the salt. The process is therefore characterized by a distinct induction period and a markedly lower rate than the activated polymerization. The key component here is the initiator, which has a crucial effect on the course of the polymerization process. On the other hand, it is an excellent kinetic tool for assessing the quality of the initiation, the purity of the system and the monomer, and the suitability of the experimental technique applied, and so on. 

The nonactivated polymerizations differ also in the extent of the inhibitory effect of water. In a CLNa-initiated polymerization, the polymerization system is able to reach the content of polymer at the equilibrium, if the water content... 

The effect of initiator type on the formation of cyclic oligomers manifests itself very markedly in the nonactivated anionic polymerization of CL [24]. When the process is initiated by the sodium salt of lactam, the formation of macrocycles is kinetically controlled the concentration of the cycles pronouncedly exceeds the equilibrium values, in similar fashion to cationic polymerization. In contrast, when the magnesium salts of CL or ethyl magnesium bromide are used as initiators, a considerable suppression of cyclization reactions was demonstrated for... 

In a nonactivated polymerization, which is an order of magnitude slower from the outset, the polymerization of PD runs as a heterogeneous process, with its conversion-time dependences being linear at least up to 50% conversion (formal zero-order kinetics) [106]. The high values of molar mass that are attained in this way confirm a low concentration of the growth centers. The polymers prepared by nonactivated polymerization contain no labile structures, which otherwise arise from side reactions [107], and also show a better thermal stability than those synthesized by activated polymerization [108] this should be true also for the CL polymerization. 

An anionic polymerization of PD, accelerated by CO2 or by potassium 2-pyrrohdone carboxylate, represents a special case [34] that enables the preparation of a relatively thermally stable polymer with a high molar mass. Its kinetics resembles that of the nonactivated polymerization [109, 110]. 

In spite of a marked acceleration of the polymerization process due to the presence of NIL, some features of the nonactivated polymerization remain preserved. 

---