Polymerization reactions, condensation

These last expressions provide two very useful views of the progress of a condensation polymerization reaction with time. Equation (5.14) describes how the concentration of A groups asymptotically approaches zero at long times Eq. (5.17) describes how the degree of polymerization increases linearly with time. 

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. 

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. ... 

There are innumerable industrially significant reactions that involve the formation of a stable intermediate product that is capable of subsequent reaction to form yet another stable product. These include condensation polymerization reactions, partial oxidation reactions, and reactions in which it is possible to effect multiple substitutions of a particular functional group on the parent species. If an intermediate is the desired product, commercial reactors should be designed to optimize the production of this species. This section is devoted to a discussion of this and related topics for reaction systems in which the reactions may be considered as sequential or consecutive in character. 

Figure 14.1.1 The formation of cellulose during a condensation polymerization reaction in which each new link of glucose monomers releases a water molecule.

Figure 2.3 In the first step, the mixture is emulsified by stirring, and in the second step, an amorphous network of glassy material is prepared at room temperature by the hydrolysis of suitable monomers. The reaction proceeds to a condensation polymerization reaction, followed by subsequent formation of the sol to the gel and xerogel stages. (Adopted from Merck.com)...

Classify each polymerization reaction as an addition or condensation polymerization reaction. 

In this section, you learned how to recognize addition and condensation polymerization reactions. You examined the structures and functions of several important biological molecules, such as proteins, amino acids, carbohydrates, DNA, and lipids. In the next section, you will examine the risks and benefits of manufacturing and using organic compounds. 

Compare addition polymerization reactions with condensation polymerization reactions. 

Our interest in such compounds stems mainly from the possibility that they might be useful precursors to new classes of phosphorus-containing polymers or cyclic oligomers. Functional linkages such as E = NSiMe3 or CR SiMe3 could serve as sites for condensation-polymerization reactions, leading to novel cyclic or polymeric sys terns, ... 

Consider the reversible condensation polymerization reaction of a hydroxyacid A to form a polyester polymer,... 

Polyethylene is formed by addition of C2H4 molecules, which are merely linked together without the elimination of any reactant atoms. When other polymers are formed, molecules are linked together, and particular atoms break loose to form additional products. When water (H20) is the additional product, the reaction is called a condensation reaction. Often the reactants are not simple hydrocarbons but are more complex organic molecules. The formation of nylon is a condensation polymerization reaction. In Activity 5.5 students will prepare a condensation polymer and use it to create a macrosculpture. 

Phenol-formaldehyde adhesives are produced by a condensation polymerization reaction between phenol and formaldehyde. The phenolics used for exterior particleboard are made at a formalde-hyde/phenol ratio greater than 1.0 i.e., they are classified as resoles and additional formaldehyde is not required to complete the curing reaction to a highly cross-linked network structure. Many characteristics can be incorporated into the adhesives by changes in the F/P ratio, condensation pH, and condensation time. The reactive solids content is normally between kO and 50 percent since the stability and viscosity are adversely affected at higher solids. 

During the early 1960 s a new class of chemicals containing one or more double bonds was used to treat wood vinyl type monomers that could be polymerized into the solid polymer by means of free radicals (2). This vinyl polymerization was an improvement over the condensation polymerization reaction because the free radical catalyst was neither acidic nor basic, nor does the reaction leave behind a reaction product that must be removed from the final composite, such as water. The acid and base catalysts used with the other treatments degrade the cellulose chain and cause brittleness of the composite. Vinyl polymers have a large range of properties from soft rubber to hard brittle solids depending upon the groups attached to the carbon-carbon backbone. 

We focus our attention in this experiment on synthetic polymers and the basic mechanism by which some of them are formed. The two most important types of reactions that are employed in polymer manufacturing are the addition and condensation polymerization reactions. The first is represented by the polymerization of styrene and the second by the formation of nylon. 

Ion-exchange polymeric resins are the most important types of exchangers currently in use [113-123], The first, totally organic ion-exchange resin was synthesized in 1935 by Adams and Holmer, when they produced a phenol-formaldehyde cation-exchange resin and an amine-formaldehyde anion-exchange resin, both obtained with the help of condensation polymerization reactions [113], In 1944, D Alelio synthesized styrene-based polymeric resins, which could be modified to obtain both cationic- and anionic-exchange resins. The majority of the resins commercially applied currently are of this type, for example, Amberlite IR-20, Lewatit S-100, Permutit Q, Duolite, C-20, Dowex-50, and Nalcite HCR. 

A typical example of a condensation polymerization reaction is the reaction between a poly functional alcohol (e.g. a glycol) and a dicarboxylic acid (e.g. terephthalic acid). 

Condensation polymerizations are equilibrium reactions, which means they eventually stop reacting when small molecular weight reaction products like water are no longer removed from the system. These characteristics of the condensation polymerization reaction also have an effect on the chemical properties of such plastics. In the presence of water, particularly at high temperatures, polyethylene terephthalate begins to hydrolyze and low molecular weight oligomers are produced which can be transferred into a food in contact with the plastic. 

It is clear that Tgxp is a function of curing conversion or molecular weight (for linear polymers) at adiff. One can observe a noticeable difference between T xp and T for such processes of polymer synthesis as polyaddition or condensation polymerization reactions. It is especially important for polymers with high T . For many heat-resistant polymers, T is higher than the temperature limit of their chemical decomposition. We can never reach natural T for these polymers. For such polymers, one really measures only Tgxp, the value of which depends on the reaction conditions. For structure-glass transition temperature correlations of networks, T is the most important quantity. 

Finally, the solvent isotope effect observed in the crystallization of zeolite A provides further insight into the mechanism. The deuteroxide anion (0D") is a stronger base than OH and should promote the depolymerization equilibria.(32) Also, D20 is more structured than H20 and should promote nucleation.(33) The isotope effect leading to a slower rate of reaction will occur in the condensation polymerization reaction leading to crystal growth, which involves elimination of both H20 and OH". (2) It is a combination of all these factors that lead to the observed nucleation rate. 

In this study, we have shown that both alcohol and D20 have an Important effect on the nucleation and crystal growth of zeolites with Si/Al ratios between 1-2. In the case of alcohol, the formation of large pore zeolites such as zeolites X or Y is markedly accelerated at low alcohol levels. We attribute this to a stabilization of the cation-water complex and structured H20 which act as templates. However, at high alcohol levels, the structure of water disintegrates and leads to the formation of more condensed zeolites such as sodalite or cancrinite. Synthesis of zeolite A in D20 is slower than that in water, which primarily arises from the primary and secondary isotope effect during the condensation polymerization reactions necessary for zeolite growth. 

Segmented copolymers are usually synthesized by condensation polymerization reactions (5, 7, 9). The reaction components consist of a difunctional soft segment, the basic hard segment component, and a chain extender for the hard segment. 

Falling off of the log viscosity-time cure curve can also occur due to dewetting, or wall slip, at the cone-sample interface. This occurs rarely, in our experience, and probably more with highly filled samples as gelation is approached. A kinetic order greater than unity could also produce a curvature similar to C, but evidence of such kinetic orders for condensation polymerization reactions has not been reported from chemorheological studies, to our knowledge. (Certain types of addition polymerization reactions may show non-first-order viscosity kinetics.)(13)... 

Cyclotrimerization of polyfunctional aryl acetylenes offers a unique route to a class of highly aromatic polymers of potential value to the micro-electronics industry. These polymers have high thermal stability and improved melt planarization as well as decreased water absorption and dielectric constant, relative to polyimides. Copolymerization of two or more monomers is often necessary to achieve the proper combination of polymer properties. Use of this type of condensation polymerization reaction with monomers of different reactivity can lead to a heterogeneous polymer. Accordingly, the relative rates of cyclotrimerization of six para-substituted aryl acetylenes were determined. These relative rates were found to closely follow both the Hammett values and the spectroscopic constants A h and AfiCp for the para substituents. With this information, production of such heterogeneous materials can be either avoided or controlled. 

Discoveries made in the late 1970s of electrical conductivity in conjugated polymers spawned a monumental interest in the study of these materials, which are ideally suited for synthesis via cross-coupling reactions. Yamamoto was the first to realize this possibility with a regiochemicahy defined synthesis of poly(/ -phenylene) formed via the Kumada-Corriu protocol. Since then, various cross-coupling reactions have been applied in condensation polymerization reactions,with the Suzuki and Sonogashira protocols gaining the most widespread use. 

In this chapter, we report the results of a study of the synthesis of a more complete series of polymers, la-Ih, by the same low-temperature condensation polymerization reaction (equation 1), All these new polymers were characterized by NMR spectroscopy, gel permeation chromatography (GPC), thermal analysis (differential scanning calorimetry [DSC] and ther-mogravimetric analysis [TGA]), and elemental analysis. 

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