Synthesis, of polymers

Two broad classes of polymers are based on the two types of polymerization reactions addition polymerization and condensation polymerization of monomers. Most high-volume thermoplastics such as PP, PE, PS, and PVC are addition polymers. Those such as nylons or PC are examples of condensation polymers. 

TABLE 3.1 Glass Transition Temperature of Common Plastics 

Low-density polyethylene (LDPE) -100 Plastic film, bags, and containers 

High-density polyethylene (HDPE) -100 Bottles, milk jugs, toys 

Polypropylene (PP) -20 Bottle caps, tape, film, fiber 

Carothers in 1929 made the classical subdivision of polymers into two main groups, condensation and addition polymers. Condensation polymers, are characteristically formed by reactions involving the elimination of a small molecule, such as water, in each step. Polyester formation is a good example of this type of polymerisation. Bifunctional monomers react with each other with the elimination of water as shown in Reaction 6.1. 

In addition polymers, no loss of small molecules takes place. The most important group of addition polymers are synthesised from unsaturated vinyl monomers, see Reaction 6.2. 

Only growth reaction adds repeating units one at a time to the chain. Any two molecnlar species present can react. 

Monomer concentration decreases steadily throughout the reaction. Monomer disappears early in reaction at a DP 10, less than 1% monomer remains. 

High polymer is formed at once. Polymer molecular weight changes little throughout the reaction. Polymer molecnlar weight rises steadily throughout the reaction. 

Gravity acts on molecules, and, as in a gas, it has an effect on their concentration. This effect perturbs the (monophasic) state of a solution. 

Using Boltzmann s law, we can calculate the concentration of the dissolved material in terms of the height h, measured from the bottom of the vessel containing the solution. The concentration C(h) reads 

In this example, the effect is perceptible, even experimentally. However, the experiments are generally made with samples of molecular mass smaller than M = 107 and, in this case, the concentration gradient resulting from gravity is negligible. 

Oligomerization continues to give polymers containing many subunits. To control the temperature of these highly exothermic reactions, to minimize Ei (see footnote on p. 329), and to maximize polymer length, industrial processes are executed with extensive cooling. 

In Summary Catalytic acid causes alkene-alkene additions to occur, a process that forms dimers, trimers, oligomers containing several components, and finally polymers, which are composed of a great many alkene subunits. 

Many alkenes are suitable monomers for polymerization. Polymerization is exceedingly important in the chemical industry, because many polymers have desirable properties, such as durability, inertness to many chemicals, elasticity, transparency, and electrical and thermal resistance. 

Although the production of polymers has contributed to pollution— many of them are not biodegradable—they have varied uses as synthetic fibers, films, pipes, coatings, and molded articles. Polymers are also being used increasingly as coalings for medical implants. Names such as polyethylene, poly(vinyl chloride) (PVC), Teflon, polystyrene, Orion, and Plexiglas (Table 12-3) have become household words. 

Acid-catalyzed polymerizations, such as that described for poly(2-methylpropene), are carried out with H2SO4, HF, and BF3 as the initiators. Because they proceed through carbocation intermediates, they are also called cationic polymerizations. Other mechanisms of polymerizations are radical, anionic, and metal catalyzed. 

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A second approach involved direct chemical synthesis of polymers by connecting appropriately... 

L. B. Sokolov, Synthesis of Polymers by Polycondensation, Israel Program for Scientific Translation, Jemsalem, Israel, 1968, pp. 60—71. 

Mullen, K. (1999). Organic chemistry and the synthesis of well-defined molecules, in Synthesis of Polymers, ed. Schltiter, A.-D. (Wiley-VCH, Weinheim) p. I. 

Vaidyanathan, R., and El-Halwagi, M. M. (1996). Computer-Aided synthesis of polymers and blends with target properties. Ind. Eng. Chem. Res., 35,627-634. 

The facile a,a diacylation with arylisocyanates has been applied to the synthesis of polymers (434-436), while the monoacylation products have been used as intermediates for the synthesis of substituted a-quinolones and their sulfur analogs (437). 

In the synthesis of polymers it is very important to control the configuration of the multiple stereogenic centers but free radical methods generally fail to give significant stereochemical control (96T(52)4181). To compare the effects of several chiral and achiral auxiliary groups, acrylamides of type 110 were studied. 

As discussed in Section 7.3, conventional free radical polymerization is a widely used technique that is relatively easy to employ. However, it does have its limitations. It is often difficult to obtain predetermined polymer architectures with precise and narrow molecular weight distributions. Transition metal-mediated living radical polymerization is a recently developed method that has been developed to overcome these limitations [53, 54]. It permits the synthesis of polymers with varied architectures (for example, blocks, stars, and combs) and with predetermined end groups (e.g., rotaxanes, biomolecules, and dyes). 

The controlled synthesis of polymers, as opposed to their undesired formation, is an area that has not received much academic interest. Most interest to date has been commercial, and focused on a narrow area the use ofchloroaluminate(III) ionic liquids for cationic polymerization reactions. The lack of publications in the area, together with the lack of detailed and useful synthetic information in the patent literature, places hurdles in front of those with limited loiowledge of ionic liquid technology who wish to employ it for polymerization studies. The expanding interest in ionic liquids as solvents for synthesis, most notably for the synthesis of discrete organic molecules, should stimulate interest in their use for polymer science. 

A long-standing goal in polyolefins is the synthesis of polymers bearing polar functional groups such as acrylate, esters, or vinyl ethers, etc [24,40]. These copolymers might endow polyolefins with useful properties such as adhesiveness, dyeability, paintability, and print-ibility. Advances have recently been made in polymerizing polar monomers with cationic metallocene catalysts... 

The use of light olefins, diolefins, and aromatic-based monomers for producing commercial polymers is dealt with in the last two chapters. Chapter 11 reviews the chemistry involved in the synthesis of polymers, their classification, and their general properties. This book does not discuss the kinetics of polymer reactions. More specialized polymer chemistry texts may be consulted for this purpose. 

The synthetic strategy towards the copolymers is shown in Figure 16-3. The use of bifunctional monomers in a Heck reaction allows the synthesis of polymers, and the great potential of this approach has been demonstrated previously [53-55]. The syntheses have been described in detail by Hilberer el al. [16],... 

The rapid development of macromoiecular chemistry has recently brought to light a number of most interesting problems related to the synthesis of polymers with unusual properties. The chemistry of polyconjugated systems undoubtedly occupies a leading place among these problems. 

RAFT polymerization lends itself to the synthesis of polymers with thiol end groups. Several groups have utilized the property of thiols and dilhioesLers to bind heavy metals such as gold or cadmium in preparing brushes based on gold film or nanoparticles1 8 761 763 and cadmium selenide nanoparticles.763 76 1... 

An objective in this research was the synthesis of polymers with Si-H head-groups. Thus guided by the results of model experiments (Sect. ILF.) the synthesis of poly(a-methylstyrene)(PaMeSt) with Si-H head-group (HSi-PaMeSt) was undertaken. 

Fairly recently, another method for obtaining polymer materials with uniaxial orientation has been developed. It is the directed polymerization i.e. the synthesis of polymers under conditions at which the material attains instanteneously the oriented structure. The formation of crystals from the macromolecules in an extended conformation occurs in those polymerizing systems simultaneously with polymerization22. ... 

ADMET is quite possibly the most flexible transition-metal-catalyzed polymerization route known to date. With the introduction of new, functionality-tolerant robust catalysts, the primary limitation of this chemistry involves the synthesis and cost of the diene monomer that is used. ADMET gives the chemist a powerful tool for the synthesis of polymers not easily accessible via other means, and in this chapter, we designate the key elements of ADMET. We detail the synthetic techniques required to perform this reaction and discuss the wide range of properties observed from the variety of polymers that can be synthesized. For example, branched and functionalized polymers produced by this route provide excellent models (after quantitative hydrogenation) for the study of many large-volume commercial copolymers, and the synthesis of reactive carbosilane polymers provides a flexible route to solvent-resistant elastomers with variable properties. Telechelic oligomers can also be made which offer an excellent means for polymer modification or incorporation into block copolymers. All of these examples illustrate the versatility of ADMET. 

K. B. Wagener, Acyclic Diene Metathesis (ADMET) Polymerization, in Synthesis of Polymers, A. D. Schluter (Ed.), Materials Science and Technology Series, Wiley, Weinheim, 1999. 

Polymers like those in the poly aniline family interchange protons and anions with the solution, allowing a local modulation of pH. Composites that interchange cations allow the modulation of any cation concentration. Efforts are being devoted to the synthesis of polymer or polymeric derivatives having great cationic specificity. 

M.12 A compound produced as a by-product in an industrial synthesis of polymers was found to contain carbon, hydrogen, and iodine. A combustion analysis of 1.70 g of the compound produced 1.32 g of C02 and 0.631 g of H20. The mass percentage of iodine in the compound was determined by-converting the iodine in a 0.850-g sample of the compound into 2.31 g of lead(II) iodide. What is the empirical formula of the compound Could the compound also contain oxygen Explain your answer. 

Anionic polymerizations are well suited for the synthesis of polymers fitted at chain end with reactive functions. Block copolymers can result from reactions between suitable functions carried by two different functional precursors. In some cases the carbanionic sites themselves are the reactive functions. In other cases, functional polymers (obtained anionically, or by other methods) can be reacted with low molecular weight coupling agents. Here are a few examples ... 

The synthetic approach is very simple and does not require any special set up. In a typical room temperature reaction, 1.0 mL aqueous solution of cadmium chloride was added to 20 mL aqueous solution of soluble starch in a 50 mL one-necked round-bottom flask with constant stirring at room temperature. The pH of the solution was adjusted from 6 to 11 using 0.1 M ammonia solution. This was followed by a slow addition of 1.0 mL colourless selenide ion stock solution. The mixture was further stirred for 2 h and aged for 18 h. The resultant solution was filtered and extracted with acetone to obtain a red precipitate of CdSe nanoaprticles. The precipitate was washed several times and dried at room temperature to give a material which readily dispersed in water. The same procedure was repeated for the synthesis of PVA and PVP - capped CdSe nanoparticles by replacing the starch solution with the PVA and PVP polymers while the synthesis of elongated nanoparticles was achieved by changing the Cd Se precursor ratio from 1 1 to 1 2. The synthesis of polymer capped ZnSe nanoparticles also follows the same procedure except that ZnCb solution was used instead of CdCb solution. 

There are three general approaches to the synthesis of polymer-clay nanocomposites. In the first approach, a monomer or precursor is mixed with organophilic clay and followed by polymerization. This in situ polymerization technique was first developed by the... 

Representative condensation polymers are listed in Table I. The list is by no means exhaustive, but it serves to indicate the variety of condensation reactions which may be employed in the synthesis of polymers. Cellulose and proteins, although their syntheses have not been accomplished by condensation polymerization in the laboratory, nevertheless are included within the definition of condensation polymers on the ground that they can be degraded, hydrolytically, to monomers differing from the structural units by the addition of the elements of a molecule of water. This is denoted by the direction of the arrows in the table, indicating depolymerization. 

Pyun, J., Kowalewski, T. and Matyjaszewski, K. (2003) Synthesis of polymer brushes using atom transfer radical polymerization. Macromol. Rapid Commun., 24, 1043-1059. 

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