Chemical reaction condensation polymerization

Cure — A process of changing the properties of a polymer by a chemical reaction (condensation, polymerization, or addition). In elastomers it means mainly cross-linking or vulcanization. 

The scaleup of polymerization processes is conceptually identical to the scaleup of ordinary chemical reactions. The principal difference is that polymer systems are more likely to be highly viscous and in laminar flow. Although polymer melts can be markedly non-Newtonian, this is rarely a critical factor in the scaleup of polymer reaction and recovery systems. Vinyl polymerizations have strong exotherms so that parametric sensitivity and thermal runaways can be a problem, but so do many other chemical reactions. Condensation polymerizations tend to be equilibrium-limited, but so do many other chemical reactions. 

Chemical reaction monitoring Polymerizations, esterifications and other condensation reactions, diazo reactions, oxidation, and reduction On-line and dip-probe applications... 

Changes in the color of red wines that occur during aging are due to the anthocyanins undergoing chemical reactions and polymerization with the other wine compounds. More than 100 structures belong to the pigment families of anthocyanins, pyranoanthocyanins, direct flava-nol-anthocyanin condensation products, and acetaldehyde-mediated... 

Polymerization is an addition reaction of a basic building-block that remains chemically unchanged, except for the absence of the double bond, after the reaction. Condensation polymerization is a substitution reaction. Two groups of reactive compounds of the same or different types react with one another. Low molecular secondary products such as water, ammonia, hydrogen chloride, alcohols, etc. are produced in the reaction. 

In the last section we examined some of the categories into which polymers can be classified. Various aspects of molecular structure were used as the basis for classification in that section. Next we shall consider the chemical reactions that produce the molecules as a basis for classification. The objective of this discussion is simply to provide some orientation and to introduce some typical polymers. For this purpose a number of polymers may be classified as either addition or condensation polymers. Each of these classes of polymers are discussed in detail in Part II of this book, specifically Chaps. 5 and 6 for condensation and addition, respectively. Even though these categories are based on the reactions which produce the polymers, it should not be inferred that only two types of polymerization reactions exist. We have to start somewhere, and these two important categories are the usual place to begin. 

Polymerization. Thermal polymerization or curing of an ink film at elevated temperatures can foUow many different chemical paths. Condensation and cross-linking reactions may be accompHshed with or without the use of catalysts. However, this method of drying generally has not been widely used for printing inks, except those used for metal and glass decoration, and some clear coatings. 

The diacids are characterized by two carboxyHc acid groups attached to a linear or branched hydrocarbon chain. AUphatic, linear dicarboxyhc acids of the general formula HOOC(CH2) COOH, and branched dicarboxyhc acids are the subject of this article. The more common aUphatic diacids (oxaUc, malonic, succinic, and adipic) as weU as the common unsaturated diacids (maleic acid, fumaric acid), the dimer acids (qv), and the aromatic diacids (phthaUc acids) are not discussed here (see Adipic acid Maleic anhydride, maleic acid, and fumaric acid Malonic acid and derivatives Oxalic acid Phthalic acid and OTHERBENZENE-POLYCARBOXYLIC ACIDS SucciNic ACID AND SUCCINIC ANHYDRIDE). The bihinctionahty of the diacids makes them versatile materials, ideally suited for a variety of condensation polymerization reactions. Several diacids are commercially important chemicals that are produced in multimillion kg quantities and find appHcation in a myriad of uses. 

Determine the worst-case gas mixture combustion charac teris-tics, system pressure, and permissible pressure drop across the arrester, to help select the most appropriate element design. Not only does element design impac t pressure drop, but the rate of blockage due to particle impact, liquid condensation, and chemical reaction (such as monomer polymerization) can make some designs impractical even if in-service and out-of-seivdce arresters are provided in parallel. 

Process in wliich the addition of heat, catalyst or both, with or without pressure, causes the physical properties of the plastic to change through a chemical reaction. Reaction may be condensation, polymerization or addition reactions. 

In recent years, the rate of information available on the use of ion-exchange resins as reaction catalysts has increased, and the practical application of ion-exchanger catalysis in the field of chemistry has been widely developed. Ion-exchangers are already used in more than twenty types of different chemical reactions. Some of the significant examples of the applications of ion-exchange catalysis are in hydration [1,2], dehydration [3,4], esterification [5,6], alkylation [7], condensation [8-11], and polymerization, and isomerization reactions [12-14]. Cationic resins in form, also used as catalysts in the hydrolysis reactions, and the literature on hydrolysis itself is quite extensive [15-28], Several types of ion exchange catalysts have been used in the hydrolysis of different compounds. Some of these are given in Table 1. 

The most common form of step growth polymerization is condensation polymerization. Condensation polymers are generally formed from simple reactions involving two different monomers. The monomers are difunctional, having a chemically reactive group on each end of their molecules. Examples of condensation polymerization are the formation of nylon 66, a polyamide, and of poly(ethylene terephthalate), a polyester. Because condensation poly-... 

The problem of achieving the highest possible molecular weight in a linear condensation polymerization resolves itself into the problem of reducing the number of end groups to the lowest possible value. Just as a chemical reaction cannot be carried to absolute completion, the... 

The combined results of kinetic studies on condensation polymerization reactions and on the degradation of various polymers by reactions which bring about chain scission demonstrate quite clearly that the chemical reactivity of a functional group does not ordinarily depend on the size of the molecule to which it is attached. Exceptions occur only when the chain is so short as to allow the specific effect of one end group on the reactivity of the other to be appreciable. Evidence from a third type of polymer reaction, namely, that in which the lateral substituents of the polymer chain undergo reaction without alteration in the degree of polymerization, also support this conclusion. The velocity of saponification of polyvinyl acetate, for example, is very nearly the same as that for ethyl acetate under the same conditions. ... 

Combined condensation of melamine and of the acid residue is also shown by the phosphate and borate. In these cases however, the polymeric dehydrated compound derived from the acid is thermally stable up to above 500 C allowing chemical reactions with melamine condensation products simultaneously formed. The resulting material is stable to 950 C (phosphate, ca 30% of original salt) or to above 1100 C (borate, ca. 20% of original salt). 

The refractory compounds in the HMW DOM pool seems to be generated through abiotic reactions that act to link degradation products into macromolecules. These new chemical bonds create molecular structures that enhance the overall refractory nature of the DOM. The chemical changes lead to increased crosslinking, aromaticity, cyclization, esterification, and nitrogen depletion. The general types of chemical reactions responsible are oxidations, polymerizations, and condensations. Considerable debate exists as to whether these reactions are wholly abiotic or whether they are, at least in part, microbially mediated. 

Many of the common condensation polymers are listed in Table 1-1. In all instances the polymerization reactions shown are those proceeding by the step polymerization mechanism. This chapter will consider the characteristics of step polymerization in detail. The synthesis of condensation polymers by ring-opening polymerization will be subsequently treated in Chap. 7. A number of different chemical reactions may be used to synthesize polymeric materials by step polymerization. These include esterification, amidation, the formation of urethanes, aromatic substitution, and others. Polymerization usually proceeds by the reactions between two different functional groups, for example, hydroxyl and carboxyl groups, or isocyanate and hydroxyl groups. 

A wide variety of chemical reactions can occur following ionization or excitation of a molecule in both gaseous and condensed phases. These may be of uni-molecular or bi-molecular nature, initiated by electrons, ions or by the transformations of excited or ionized molecules. These reactions include, but are not limited to, dissociation, elimination of atoms and smaller molecules (H, H2, etc.), transfer of H, H2, H, and H2, fragmentation, ion-molecule reaction, luminescence and energy transfer, neutralization, chain reaction, condensation, and polymerization, etc. These reactions will not be reviewed in this chapter but may be found elsewhere in this book. A brief summary is also found in Chapters 4 and 5 of Ref. 2. In the next section, some features of yields and mechanisms following excitation and/ or ionization in the liquid phase are discussed with special reference to water. 

The aminophenols are chemically reactive, undergoing reactions involving both the aromatic amino group and the phenolic hydroxyl moiety, as well as substitution on the benzene ring. Oxidation leads to the formation of highly colored polymeric quinoid structures. 2-Aminophenol undergoes a variety of cyclization reactions. Important reactions include alkylation, acylation, diazonium salt formation, cyclization reactions, condensation reactions, and reactions of the benzene ring. 

As outlined earlier, three methods of polymerization have been established for the preparation of thiophenes, viz. electrochemical polymerization [189, 190], oxidative chemical polymerization using Lewis acid catalysts such as FeCl3 [191,192], and step-growth condensation polymerization using transition metal-catalyzed coupling reactions [lj]. 

A large number of successful experimental studies which tried to work out plausible chemical scenarios for the origin of life have been conducted in the past (Mason, 1991). A sketch of a possible sequence of events in prebiotic evolution is shown in Figure 3. Most of the building blocks of present day biomolecules are available from different prebiotic sources, from extraterrestrial origins as well as from processes taking place in the primordial atmosphere or near hot vents in deep oceans. Condensation reactions and polymerization reactions formed non-in-structed polymers, for example random oligopeptides of the protenoid type (Fox... 

---