Step-growth polymerizations polyesters

The preceding discussions of the kinetics and molecular weight distributions in the step-growth polymerization of AB monomers are clearly exemplified by the esterification reactions of such monomers as glycolic acid or co-hydroxydecanoic acid. Therefore one method for polyester synthesis is the following ... 

Even within a particular class of polymers made by step-growth polymerization, monomer composition can be varied to produce a wide range of polymer properties. For example, polyesters and polyamides can be low-Tg, amorphous materials or high-Tg, liquid crystalline materials depending on the monomer composition. 

Nearly all of the polymers produced by step-growth polymerization contain heteroatoms and/or aromatic rings in the backbone. One exception is polymers produced from acyclic diene metathesis (ADMET) polymerization.22 Hydrocarbon polymers with carbon-carbon double bonds are readily produced using ADMET polymerization techniques. Polyesters, polycarbonates, polyamides, and polyurethanes can be produced from aliphatic monomers with appropriate functional groups (Fig. 1.1). In these aliphatic polymers, the concentration of the linking groups (ester, carbonate, amide, or urethane) in the backbone greatly influences the physical properties. 

Hyperbranched polyesters are prepared by the step-growth polymerization of A13,-type monomers where A and B are —OH and —COOH groups or derivatives such as CH3COO-, HO-CH2CH2-O-, (CH3)3SiO—, -COOCH3, or -COC1... 

Linear polyurethanes, 26 Linear step-growth polymerizations, 13 Lipase-catalyzed polyesterifications, 83 Lipases, 82, 84 catalytic site of, 84 Liquefied MDIs, 211, 226-227 Liquid carbon dioxide, 206 Liquid-castable systems, 201 Liquid crystal devices (LCDs), alignment coating for, 269-270 Liquid crystalline aromatic polyesters, 35 Liquid crystalline polyesters, 25, 26, 48-53... 

Step growth polymerization. Important polymers manufactured by step growth are polyamides (nylons), polyesters, and polyurethanes. 

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-... 

An unsaturated polyester resin consists of a linear polyester whose chain contains double bonds and an unsaturated monomer such as styrene that copolymerizes with the polyester to provide a cross-linked product. The most common unsaturated polyester is made by step growth polymerization of propylene glycol with phthalic and maleic anhydrides. Subsequent treatment with styrene and a peroxide catalyst leads to a solid, infusible thermoset. 

Aliphatic polyesters occupy a key position in the field of polymer science because they exhibit the remarkable properties of biodegradability and biocompatibihty, which opens up a wide range of applications as environmentally friendly thermoplastics and biomaterials. Three different mechanisms of polymerization can be implemented to synthesize aliphatic polyesters (1) the ring-opening polymerization (ROP) of cyclic ketene acetals, (2) the step-growth polymerization of lactones, and (3) the ROP of lactones (Fig. 1). 

Write a mechanism for a step-growth polymerization, as in the formation of a polyester, polyamide, polyurethane, epoxy resin of phenol-formaldehyde polymer. 

Brunelle et al. [157] developed high-yielding syntheses of cyclic esters derived from 1,4-aromatic acyl chlorides and diols. Hodge et al. [158] used a solid support and step growth polymerization to produce a polyester chain followed by treatment with a metal catalyst, most often Bun2SnO, to affect intrachain transesterification and release of the cyclic esters into the solution phase. 

Carothers pioneering studies were also based on aliphatic polyesters and then culminated in laying the foundations for condensation and step-growth polymerization and in establishing a relationship between molar mass and extent of reaction and the stoichiometric imbalance of functional groups. Fundamental studies relating structure to properties were carried out using these polymers. 

One important group of condensation polymers is the polyesters. The most important commercial polyester is formed from the reaction of terephthalic acid (a diacid) with ethylene glycol (a diol). This polymerization occurs in a stepwise fashion (hence the name step growth polymerization). First, one carboxylic acid group of a diacid molecule and one hydroxy group of a diol molecule combine to form an ester, with the loss of water. Then a second diol molecule reacts with the unreacted caiboxylic group on the other end of the diacid molecule, or a second diacid molecule reacts with the unreacted hydroxy group of the diol. Continuation of this process adds a new monomer unit at... 

Note that the polymerizations of lactones and lactams give polyesters and polyamides, respectively, polymers that can also be synthesized by conventional step-growth polymerization from noncyclic monomers. Although the polymer prepared from cyclic monomers looks like a condensation polymery in strict terms it is not, because no small-molecule byproduct was pro-... 

Step-Growth Polymerization Synthesis of Polyesters in the Melt Step-Growth Polymerization Synthesis of a Polyurethane Foam... 

In this experiment, both linear and crosslinked polyesters are synthesized by step-growth polymerization The reactions are carried out in the melt (or neat), meaning that no solvents are used in the preparation and the final product does not have to be purified. Preparations such as these are sometimes called green reactions. 

Step-growth polymerization, 22, 24-25, 23, 84-86, 86,90-92,114-115, 261 compared with chain-growth polymerization, 88-89, 88-89 interfacial polymerization, 91-92 laboratory activities on synthesis of nylon, 228-230 synthesis of polyesters in the melt, 231-233 synthesis of polyurethane foam, 234-237 molar mass and, 86, 86 polycondensation of poly ethylene terephthalate), 90-91 polymers produced by, 86 types of monomers for, 90 Stereochemistry, 28, 37-39,41-42, 70 tacticity, 103-105 Stereoisomers, 41 Stereoregularity, 70 Stiffness, 142, 261 Strain, 142-143, 261 Strength... 

In a step-growth polymerization, any two monomers having the correct functionality can react with each other, or two polymer chains can combine. Most step-growth polymers are condensation polymers, bonded by some kind of condensation (bond formation with loss of a small molecule) between the monomers or the polymer segments. The most common condensations involve the formation of amides and esters. Dacron polyester is an example of a step-growth condensation polymer. 

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. 

FIGURE 3-7 Formation of dimers, trimers, etc., in the step-growth polymerization of polyesters. 

Otto Bayer was aware of the work of Staudinger and Carothers. He was particularly impressed with the latter s discovery of polyamides and its implications for the fiber and textile industries. He knew that in the condensation (linear step-growth) polymerization used to prepare nylon and polyesters a small molecule, usually water, is formed and has to be removed. 

Figure 5.21. Reaction schemes for the most common types of step-growth polymerization. Shown are (a/c) polyester formation, (b/d) polyamide formation, (e) polyamide formation through reaction of an acid chloride with a diamine, (f) transesterification involving a carboxylic acid ester and an alcohol, (g) polybenzimidazole formation through condensation of a dicarboxyhc add and aromatic tetramines, and (h) polyimide formation from the reaction of dianhydrides and diamines.

Carothers (du Pont) synthesizes the first aliphatic polyesters, establishes the principles of step-growth polymerization, and develops nylon 6,6 Julius Nieuwland develops the synthetic mbber called neoprene Poly(methylmethacrylate) (PMMA) is synthesized Hans von Chain and Sir Frank Whittle file patents for the jet engine Cathode ray tubes (CRTs) are invented by Allen B. Du Mont Ernest Ruska discovers the electron microscope magnification of 12,000 X... 

In step-growth polymerizations of commercial linear polymers the degrees of conversion are clo.se to unity. Thus, for linear nylons and polyesters, Mv//M is close to 2 as indicated by Eq. (5-36) with p =. ... 

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