Condensation polymers polycarbonates

Polycarbonates are condensation polymers made from phosgene and bisphenol A. They have high impact strength and are used in glazing, helmets, and appliance casings. 

Condensation polymers, which are also known as step growth polymers, are historically the oldest class of common synthetic polymers. Although superseded in terms of gross output by addition polymers, condensation polymers are still commonly used in a wide variety of applications examples include polyamides (nylons), polycarbonates, polyurethanes, and epoxy adhesives. Figure 1.9 outlines the basic reaction scheme for condensation polymerization. One or more different monomers can be incorporated into a condensation polymer. 

Cyclic oligomers of condensation polymers such as polycarbonates and polyesters have been known for quite some time. Early work by Carothers in the 1930s showed that preparation of aliphatic cyclic oligomers was possible via distillative depolymerization [1, 2], However, little interest in the all-aliphatics was generated, due to the low glass transition temperatures of these materials. Other small-ring, all-aliphatic cyclic ester systems, such as caprolactone, lactide... 

Interfacially formed condensation polymers such as polyesters, polycarbonates, nylons, and PUs are typically formed on a microscopic level in a chain-growth manner largely because of the highly reactive nature of the reactants employed for such interfadal polycondensations. 

A number of plastics are condensation polymers and include polyesters and nylons that are not as highly oriented as the same materials but in fiber form. Other plastics have been developed that have outstanding heat stability, strength, and other properties that allow their wide use. These plastics include polycarbonates, polyimides, polybenzimidazoles, polysulfides, polyethers, polysulfones, and polyketones. 

Bayer, A. 1878. Phenol-formaldehyde condensates. Ber. Bunsenges. Phys. Chem., 5 280, 1094. Brunelle, D.J. and Korn, M. 2005. Advances in Polycarbonates. Oxford University Press, New York. Carothers, W.H. 1929. An introduction to the general theory of condensation polymers. J. Amer. Chem. Soc., 51 2548. 

In general, substitution of polar atoms and polar groups for nonpolar or less polar moieties results in an increase in the Tg and such mechanical properties as yield stress and modulus. Thus condensation polymers such as nylons, polycarbonate (PC), and polyesters are typically higher-melting and exhibit higher Tg s, tensile strength and associated properties, but typically lower impact strengths and associated properties which require some flexibility (Table 5.3). 

Problem 16.98 (a) Show the mers of the following condensation polymers, formed from the two indicated monomers (i) Polycarbonate (Lexan). phosgene, CLC=0 + (HOC H ),C(CH ), (tough and optically clear) (ii) Kodel,... 

Much attention has been paid to the synthesis of fluorine-containing condensation polymers because of their unique properties (43) and different classes of polymers including polyethers, polyesters, polycarbonates, polyamides, polyurethanes, polyimides, polybenzimidazoles, and epoxy prepolymers containing pendent or backbone-incorporated bis-trifluoromethyl groups have been developed. These polymers exhibit promise as film formers, gas separation membranes, seals, soluble polymers, coatings, adhesives, and in other high temperature applications (103,104). Such polymers show increased solubility, glass-transition temperature, flame resistance, thermal stability, oxidation and environmental stability, decreased color, crystallinity, dielectric constant, and water absorption. 

Most condensation polymers fall into one of four major categories the polyamides, polycarbonates, polyesters, and polyurethanes. One of the first and eventually most popular synthetic polymers to be synthesized was a polyamide called nylon 66, discovered in 1935 by the American chemist Wallace Carothers (1896-1937). Nylon 66 is made in the reaction between adipic acid (hexanedioic acid, HOOC(CH2)4COOH) and hexamethylenediamine (NH2(CH2)6NH2). The equation for that reaction is as follows ... 

The acid and base sensitivity of condensation polymers whether or not under stress, e.g. polycarbonate, polyesters, polyamides and polysilanes under influence of acid or base the condensation bonds are hydrolysed under the cooperative action of mechanical stresses and the environment. A striking example is shown in Fig. 26.11, where the strength retention of PpPTA fibres is plotted versus pH after an exposure of 3 months at room temperature (Van den Heuvel and Klop). The hydrolysis of the polyamide is acid or alkali catalysed, in particular below pH = 3 and above pH = 9. 

Condensation polymers result from formation of ester or amide linkages between difunctional molecules. Condensation polymerization usually proceeds by step-growth polymerization, in which any two monomer molecules may react to form a dimer, and dimers may condense to give tetramers, and so on. Each condensation is an individual step in the growth of the polymer, and there is no chain reaction. Many kinds of condensation polymers are known. We discuss the four most common types polyamides, polyesters, polycarbonates, and polyurethanes. 

Mechanisms of degradation in condensation polymers, and the stabilisation of these polymers and non-polyolefin polymers such as poly(vinyl chloride) using organophosphites is discussed in terms of the stability of colour, thermal properties and molecular weight. Stabilisation of poly(ethylene terephthalate) and polycarbonate by organophosphites was studied experimentally. 5 refs. 

The major disadvantage of chemical depolymerization is that it is almost completely restricted to the recycling of condensation polymers, and is of no use for the decomposition of most addition polymers, which are the main components of the plastic waste stream. Condensation polymers are obtained by the random reaction of two molecules, which may be monomers, oligomers or higher molecular weight intermediates, which proceeds with the liberation of a small molecule as the chain bonds are formed. Chemical depolymerization takes place by promoting the reverse reaction of the polymer formation, usually through the reaction of those small molecules with the polymeric chains. Several resins widely used on a commercial scale are based on condensation polymers, such as polyesters, polyamides, polyacetals, polycarbonates, etc. However, these polymers account for less than 15% of the total plastic wastes (see Chapter 1). 

Hydrolysis has been the main method used for the chemical recycling of other condensation polymers, such as polyacetals and polycarbonates. Hydrolysis of polyacetals leads back to the starting monomers, formaldehyde or trioxane. Polycarbonates are polymers synthesized by the reaction of phosgene and a dihydric phenol, commonly bisphenol A. Chemical recycling of polycarbonate... 

Preparation Methods for Condensation Polymers Polyamides Polyesters Polyimides Polyurethanes Polyureas Polycarbonates Polyanhydrides... 

In addition to the separate or combined effects of heat, oxygen, and radiation, polymers may deteriorate due to exposure to water (hydrolysis) or different types of chemical agents. Condensation polymers like nylons, polyesters, and polycarbonates are susceptible to hydrolysis. Structural alteration of some polymers may occur as a result of exposure to different chemical environments. Most thermoplastics in contact with organic liquids and vapors, which ordinarily may not be considered solvents for the polymers, can undergo environmental stress cracking and crazing. This may result in a loss of lifetime performance or mechanical stability and ultimately contribute to premature mechanical failure of the polymer under stress. 

We will first discuss addition or chain-reaction polymerization and then discuss condensation or step-reaction polymers in Section 3.8. Addition polymers used in packaging include, among others, polyethylene, polypropylene, polyvinyl chloride, and polystyrene. Polyesters, nylons, and polycarbonate are condensation polymers. 

The names of some plastics, particularly condensation polymers (see Section 3.8), do not follow this customary pattern. For example, as we shall see in Chapter 4, nylons (or polyamides) have a unique numbering system related to their structure. Polycarbonate is another polymer whose name does not accurately reflect the monomer used to produce it. In this and some other cases, a generic family name is so closely associated with a particular member of a polymer family, that this family name is often used as if it represented only that particular plastic. For... 

Reaction rates are slower than for addition polymerization and lower molecular weight products are formed. Condensation polymers include polyesters, nylons, polycarbonates, formaldehyde polymers and epoxies. Compared with polymers created by addition polymerization, products of condensation reactions harden on heating (thermosetting), are brittle, poorly soluble in hydrocarbons and may be swollen but not dissolved by chlorinated liquids. More details of the synthesis processes for the condensation polymers most commonly found in heritage collections are presented next. 

Condensation polymers nylon, teflon, polymethane, polycarbonate, amino resins, alkyl resins, and silicone resins... 

Further development of linear condensation polymers resulted from the recognition that natural fibers such as rubber, sugars, and cellulose were giant molecules of high molecular weight. These are natural condensation polymers, and understanding their structure paved the way for the development of the synthetic condensation polymers such as polyesters, polyamides, polyimides, and polycarbonates. The chronological order of the development of polymers is shown in Table 1.1. 

Condensation polymers can be regarded as a sequence of monomer units containing fxmctional groups immobilized into the polymer structure. Their decomposition pathways will often be dominated by the polarity and by the reactivity of the fxmctional groups within their structure, and their thermal decomposition reactions will be ionic and selective, rather than radical and imselective. Such are the thermal degradation processes occurring in polyesters, polyamides, polycarbonates, polyurethanes, polyureas, and in several other cases. ... 

Blends of condensation polymers containing functional groups internally or at chain ends (such as polycarbonates, polyesters, polyamides, and the like) may undergo intermolecular exchange reactions when mixed in the molten... 

Also a number of condensation polymers such as Nylon 6, polycarbonate, and polyesters were studied (see Table 10.2). These polymers usually possess broad MM distributions, the value of the ratio MJM being usually around 2. From the inspection of Table 10.2 it can be seen that MALDl underestimates both and M in the case of condensation polymers and that the ratio M IM derived from MALDl spectra of polydisperse polymers is strongly underestimated, and the MM distribution is much narrower. This evidence indicates that lighter molecules are preferentially detected in MALDI-TOF instruments, causing the underestimation of the presence of larger molecules and limiting the use of MALDl for MM and MMD determinations to "monodisperse" samples. 

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