Chemistry polymer

Polymers are very large organic molecules that are either made synthetically or are of natural origin, and find use as plastics, rubber, fibers, and coatings. Polymers were first produced commercially in 1860 by modification of cellulose from wood or cotton, followed by a fully synthetic product made from phenol and formaldehyde in 1910. 

In this chapter, we will see how polymers are manufactured from monomers. We will ejq)lore the chemical mechanisms that create polymers as well as how polymerization methods affect the final molecular structure of the polymer. We will look at the effect of the chemical structure of monomers, catalysts, radicals, and solvents on polymeric materials. Finally, we will apply our molecular understanding to the real world problem of producing polymers on a commercial scale. 

Phosgene is very commonly employed in polymerisation reactions. Its role in the synthesis of polyurethanes and of polycarbonates has been described in Chapter 4, and reactions in which polymers are modified by post-treatment with COCl have been described in Chapter 10 (under the Section most appropriate to the type of functional group involved). This Section is mainly concerned with the reactions of phosgene to give novel polymers. 

Probably the simplest polymer formation reaction involving phosgene is that with the dihydric aliphatic alcohols, such as ethylene, propylene or butylene glycol viz. ethane-1,2-diol, propane-1,3-diol or butane-1,4-diol) this reaction results in the formation of linear, wax-like polymers suitable for the impregnation of materials requiring water barrier properties [1133]. 

As a final example, phenolphthalein (10.38) and related compounds react with phosgene to give high molecular weight linear polycarbonates [1434], 

A number of novel process methods have been described. For example, ultrasound [1142] and phase-transfer catalytic techniques [1085] have been employed to Increase reaction rates in the synthesis of polycarbonates. 

The copolymerization of H CO and phosgene can be induced by irradiation with 7-rays, to give materials with COCl2 HjCO = (0.001-0.005) . The thermal stability of these co-polymers was not improved relative to the homopolymer of HjCO [1490]. 

Further examples of kinetic studies will be found on pp. 36,41, and 54. POLYMER CHEMISTRY 

In one of the earliest investigations of spin trapping, olefin polymerization was employed to demonstrate the utility of the method as a qualitative probe for free-radical reactions (Chalfont et al., 1968). The polymerization of styrene, initiated by t-butoxyl radicals, proved to be an excellent system with which to obtain spectra attributable to spin adducts with MNP (a) of the initiator radical 

The reactivities of various vinyl monomers towards different initiating radicals have been reported in a series of papers by Sato and Otsu and their colleagues. Some of the results obtained by this group were summarized recently (Sato et al., 1979), but the data are based on steady-state spin-adduct ratios it has already been seen (p. 29) that this approach involves assumptions which cannot generally be justified, although the fact that the relative reactivities which were obtained proved to be virtually independent of the ratio of monomers used lends some support to the validity of the results. 

As shown in Fig. 2, oidy some epoxy-phenolic compositions and a limited number of heterocyclic polymers exhibit long-term thermal stability at 200°C and higher temperatures. In the heterocyclic series, only polybenzimidazoles, polyimides and polyphenylquinoxahnes have been subjected to extensive testing at high temperature. Several classification schemes are commonly used in the literature to represent these polymers. In the following discussion, the polymer chemistry is presented in the form 

Palmer et al. [184] prepared a stable dehydro[14]annulene by reaction of a l-sUyl-2-stannylethyne and a bromoaromatic functionality. Lukevics et al. [185] synthesized unsymmetrical diynes by reactions between alkynylstannanes and terminal bromoalkynes. 

The Stille-coupHng-based polycondensations and copolymerizations are still among the most important methodologies for the synthesis of functional materials. The high level of functional group tolerance and the applied mild reaction conditions for the StiUe coupHng are very important features for the synthesis of functional oHgomers and polymers. This particular research area has recently been reviewed 

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Fiery P J 1953 Principles of Polymer Chemistry (Ithaca, NY Cornell University Press)... 

An area of great interest in the polymer chemistry field is structure-activity relationships. In the simplest form, these can be qualitative descriptions, such as the observation that branched polymers are more biodegradable than straight-chain polymers. Computational simulations are more often directed toward the quantitative prediction of properties, such as the tensile strength of the bulk material. 

H. R. Allcock, F. W. Lampe, Contemporary Polymer Chemistry Prentice-Hall, Englewood Clilfs (1990). 

In terms of the number of scientists and engi neers involved research and development in polymer chemistry is the principal activity of the chemical in dustry The initial goal of making synthetic materials that are the equal of natural fibers has been more than met it has been far exceeded What is also im... 

Our purpose in this introduction is not to trace the history of polymer chemistry beyond the sketchy version above, instead, the objective is to introduce the concept of polymer chains which is the cornerstone of all polymer chemistry. In the next few sections we shall introduce some of the categories of chains, some of the reactions that produce them, and some aspects of isomerism which multiply their possibilities. A common feature of all of the synthetic polymerization reactions is the random nature of the polymerization steps. Likewise, the twists and turns the molecule can undergo along the backbone of the chain produce shapes which are only describable as averages. As a consequence of these considerations, another important part of this chapter is an introduction to some of the statistical concepts which also play a central role in polymer chemistry. 

In Chaps. 5 and 6 we shall examine the distribution of molecular weights for condensation and addition polymerizations in some detail. For the present, our only concern is how such a distribution of molecular weights is described. The standard parameters used for this purpose are the mean and standard deviation of the distribution. Although these are well-known quantities, many students are familiar with them only as results provided by a calculator. Since statistical considerations play an important role in several aspects of polymer chemistry, it is appropriate to digress into a brief examination of the statistical way of describing a distribution. 

Throughout this discussion we have used the numerical fraction of molecules in a class as the weighting factor for that portion of the population. This restriction is not necessary some other weighting factor could be used equally well. As a matter of fact, one important type of average encountered in polymer chemistry is the case where the mass fraction of the ith component is used as the weighting factor. Defining the mass of material in the ith class as mj, we write... 

Table 1.5 Summary of the Molecular Weight Averages Most Widely Encountered in Polymer Chemistry...

P. J. Floryt whose outstanding overall contributions in polymer chemistry won him the Nobel Prize in 1974. Flory s book Principles of Polymer Chemistry contains an admirable discussion of these topics. 

Flory, P. J., Principles of Polymer Chemistry, Cornell University Press, Ithaca, N.Y., 1953. 

We saw in Chap. 1 that the ratio M /M is widely used in polymer chemistry as a measure of the width of a molecular weight distribution. If the effect of chain ends is disregarded, this ratio is the same as the corresponding ratio of n values ... 

We have not attempted to indicate the conditions of temperature, catalyst, solvent, and so on, for these various reactions. For this type of information, references that deal specifically with synthetic polymer chemistry should be consulted. In the next few paragraphs we shall comment on the various routes to polyester formation in the order summarized above and followed in Table 5.3. 

The search for substances which quahfy for proposed applications has always been a driving force for the synthesis and characterization of new compounds. This is especially true in polymer chemistry, where it is the potential of polymers as engineering materials that often stimulates research. Polymeric materials frequently fail to be serviceable in engineering applications for one of the following reasons ... 

Once the potential associated with this aspect of molecular architecture is recognized, the principles of the last section coupled with the richness of organic (and inorganic) chemistry suggest numerous synthetic possibilities. We shall not attempt to be comprehensive in discussing this facet of polymer chemistry instead we cite only a few examples of step-growth polymers which incorporate... 

Figure 6.3 Log-log plots of Rp versus concentration which verify the order of the kinetics with respect to the constituent varied, (a) Monomer (methyl methacrylate) concentration varied at constant initiator concentration. [Data from T. Sugimura and Y. Minoura, J. Polym. Sci. A-l 2735 (1966).] (b) Initiator concentration varied AIBN in methy methacrylate (o), benzoyl peroxide in styrene ( ), and benzoyl peroxide in methyl methacrylate ( ). (From P. J. Flory, Principles of Polymer Chemistry, copyright 1953 by Cornell University, used with permission.)...

It is not the purpose of this book to discuss in detail the contributions of NMR spectroscopy to the determination of molecular structure. This is a specialized field in itself and a great deal has been written on the subject. In this section we shall consider only the application of NMR to the elucidation of stereoregularity in polymers. Numerous other applications of this powerful technique have also been made in polymer chemistry, including the study of positional and geometrical isomerism (Sec. 1.6), copolymers (Sec. 7.7), and helix-coil transitions (Sec. 1.11). We shall also make no attempt to compare the NMR spectra of various different polymers instead, we shall examine only the NMR spectra of different poly (methyl methacrylate) preparations to illustrate the capabilities of the method, using the first system that was investigated by this technique as the example. 

In molecular weight determinations it is conventional to dissolve a measured mass of polymer m2 into a volumetric flask and dilute to the mark with an appropriate solvent. We shall use the symbol Cj to designate concentrations in mass per volume units. In practice, 100-ml volumetric flasks are often used, in which case C2 is expressed in grams per 100 ml or grams per deciliter. Even though these are not SI units, they are encountered often enough in the literature to be regarded as conventional solution units in polymer chemistry. 

Source Data from D. Margerison and G. C. An Introduction to Polymer Chemistry, Pergamon, Oxford, 1967. 

T erms like fundamental, molecular, and interesting have different meanings for different people. Let me e>q)lain how they apply to the presentation of polymer chemistry in this text. 

One important class of point-of-use processes utilizes a porous polymer containing reactive metals. Variations in the metal and polymer chemistry are made to optimize the process for different gas appHcations. This is an active area of development and purifiers are available for most of the principal specialty gases. 

With aldehydes, primary alcohols readily form acetals, RCH(OR )2. Acetone also forms acetals (often called ketals), (CH2)2C(OR)2, in an exothermic reaction, but the equiUbrium concentration is small at ambient temperature. However, the methyl acetal of acetone, 2,2-dimethoxypropane [77-76-9] was once made commercially by reaction with methanol at low temperature for use as a gasoline additive (5). Isopropenyl methyl ether [116-11-OJ, useful as a hydroxyl blocking agent in urethane and epoxy polymer chemistry (6), is obtained in good yield by thermal pyrolysis of 2,2-dimethoxypropane. With other primary, secondary, and tertiary alcohols, the equiUbrium is progressively less favorable to the formation of ketals, in that order. However, acetals of acetone with other primary and secondary alcohols, and of other ketones, can be made from 2,2-dimethoxypropane by transacetalation procedures (7,8). Because they hydroly2e extensively, ketals of primary and especially secondary alcohols are effective water scavengers. 

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