Polymer-forming reactions

In the polyesterification process p is directly calculated from the carboxyl group titer. Results for the polyesterification reaction between diethylene glycol and adipic acid at 166° and 202°C are plotted in Fig. 3 in accordance with the third-order equation (8). For comparison purposes, the course of the non-polymer-forming reaction of diethylene glycol with the monobasic acid, caproic, is also shown. Eq. (8) is not obeyed from zero to 80 percent esterification [l/(l—p) =l to 25], as is shown by the curvature over this region. From 80 to 93 percent esterification the reaction appears to be third order. The non-polymerforming esterification of diethylene glycol with caproic acid (and other... 

Since that time, synthetic chemists have explored numerous routes to these statistically hyperbranched macromolecular structures. They are recognized to constitute the least controlled subset of structures in the major class of dendritic polymer architecture. In theory, all polymer-forming reactions can be utilized for the synthesis of hyperbranched polymers however, in practice some reactions are more suitable than others. 

The reaction sequence used to synthesize these flexible systems involved four steps which are outlined in Figure 1. The first of these was an aromatic nucleophilic substitution, a polymer forming reaction in which 4,4 -dichlorodiphenyl sulfone reacts with various diols. The second step, an Ullmann ether reaction, gives bromine terminated products in which the bromines can be replaced by ethynyl end groups in the final stages. 

Monomer/Oligomer Synthesis. The first two steps in the four step reaction sequence of Figure 1 are capable of producing both monomer and oligomer. The first step, aromatic nucleophilic substitution, is a polymer forming reaction under the correct stoichiometric conditions. In order to favor the formation of monomer with a small amount of oligomer, the substitution was carried out at a 4 1 ratio of diol to dichlorodiphenyl sulfone. This led to a predominantly monomeric product (IV) with only the requirement that the excess diol be removed from the product to eliminate the potential presence of low molecular weight species in later reactions. 

All solvents for these solution thermolysis reactions were freshly distilled and all reactions were done in sealed glass tubes heated in a thermostatted oven. Over a wide range of solvents (DMF, naphthalene, diphenylmethane, benzene, toluene, and decalin) there was no significant variation in either isomerization rate or product composition. Reactions were done at 125°C, 155°C and 195°C and the only limitation was that DMF could not be used as the solvent in reactions at 195°C it led to substantial substrate destruction (polymer forming reactions of substrate with DMF ). Isomer compositions were ascertained both by HPLC and by NMR. 

On the other hand, diamines of low basicity do not exhibit sufficient nucleophilic character to allow them to enter into a polymer-forming reaction with the anhydride. Ideally, the diamine should exhibit a pKa of 4.5-6 [14]. Furthermore, depending on the exact chemical structure of the diamine, the basicity and the reactivity of the second amine group may be significantly influenced after reaction of the first amine-group to yield an amide linkage [14,... 

The second step of the classical polyimide synthesis, cyclodehydration or imidization, to yield the final polyimide is of equal importance to the polymer forming reaction, since ultimately the application lies in the final polyimide and its inherent properties. The final imidization step can be achieved via two... 

Derivatization of the monomer and subsequent activation to allow the monomer to enter a polymer forming reaction to yield the desired polymer. 

The preparation of polymers from heterocyclic monomers that contain polymerizable functional groups undoubtedly constitutes the most common method of incorporating heterocycles into polymeric materials. Polymer-forming reactions are of two possible types addition reactions and condensation reactions. Addition monomers in general contain a site of unsaturation, i.e. a double or triple bond, through which polymerization occurs by successive single bond formation from one monomer to the next. With condensation monomers a bond is formed between two monomers with concomitant elimination of a... 

The preparation of the related high molecular weight poly-1.4-phenylene sulfide has been accomplished by heating />-bromothio-phenolate salts in pyridine at 250° C (57). The commercially available polyethersulfones are reported to be prepared by condensation of 4.4 -dichlorodiphenyl sulfone with salts of biphenols in solvents such as dimethylsulfoxide at 150° C. The work of Bacon and Hill would suggest that both of these reactions might be carried out at considerably lower temperatures with copper (I) salts as catalysts. In addition, it has been demonstrated that copper (I) acetylides react quantitatively with aromatic iodides to yield tolanes (15, 77) therefore this reaction should also be the basis for a similar polymer forming reaction. 

In this chapter we report on an investigation of the kinetics of this reaction with several monomers. Bunnett and Levitt have studied the kinetics of nucleophilic substitution between p-substituted bromobenzenes and sodium methoxide (1) and found these reactions to be second order. Therefore, for a polymer-forming reaction between difunctional reactants, one would expect a second-order reaction with respect to the concentra-... 

In the presence of an added catalyst such as p-toluenesulphonic acid, simple esterification reactions and polyesterification reactions are second order [48]. Thus the kinetics of the catalysed reaction of lauric acid and lauryl alcohol in a medium of lauryl laurate closely parallels those of the polymer-forming reaction between adipic acid and 1,10-dodecanediol in a medium of polyester product. Second-order rate coefficients for the two reactions were [35], respectively, 45x10 equiv kg" sec and 16 X 10" equiv kg" sec . 

In principle any kind of polymer-forming reactions can be employed for foam preparation. Accordingly, all kinds of thermosetting polymers can theoretically lead to foamed materials. 

The polyisocyanate-based polymer-forming reactions can be classified into three types of reactions addition reactions, condensation reactions, and cyclotrimerization reactions. Among the isocyanate reactions shown in Table 2, the addition reaction is the major isocyanate reaction in polyurethane foam preparation. A model addition reaction is shown below ... 

Thus much of the challenge to the scientist comes from ways in which to control the polymer-forming reaction by limiting the number of points of attack in, for example, the phenol molecule. In polymer terms this means that the functionality of the phenol is modified by the use of substituents to block reactive positions or by controlling the stoichiometry. For convenience, these aspects are discussed in detail under appropriate sections below but we point out here that the approaches have general application. 

Second, it should be neutral and non-reacting, in the sense that the additive may not be a salt or an acid that can interfere with the components of the polymer-forming reaction system. Thus, all groups on the phosphorus atom must be bound to the phosphorus atom through a C-P, C-O-P or N-P bond. 

For nonelectrical insulating uses a rigid poly(ester-imide) with optical anisotropy is known, containing a diphenol with an imide structure, made from the reaction of 4-hydroxyphthalic acid with p-aminophenol [38]. The diacetylated derivate is used in the polymer forming reaction. 

Choice and Amount of Catalyst and Role of the Cu Cocatalyst. Most frequently 0.1—5 mol % (PhsP)2-PdCp and varying amounts of Cul are used in both organic and polymer-forming reactions. In cases where the haloarene is sufficiently active (typically iodoarenes), much smaller amounts (0.1—0.3%) should be sufficient. The successful start of the reaction can be monitored by the increase of turbidity of the reaction mixture, indicating the formation of insoluble ammonium halides. If very small amounts of catalyst are used, it may be necessary to add another batch to the reaction mixture until the reaction... 

One step synthesis of sulfones using formic acids (not polymers but may be useful technique for application to polymer forming reactions) [69]. 

---