Step Polymerization, Condensation Polymers

Condensation polymers are formed from monomers with functional (reactive) groups such as those shown in Fig. 3.29. 

The first step in a step reaction mechanism is the formation of esters or amides from the diols and diacids or diacids and diamines, respectively. From these intermediates, the polymerization reaction (second step) proceeds. Because the first step is a faster reaction than the second, the monomer is used up quickly. During the two steps of the reaction, small molecules such as H2O or CH3OH are eliminated. Water is the most frequent byproduct molecule, for example from the reaction between a diacid and a dialcohol. Unlike addition polymers, condensation polymers, because they incorporate functional groups, generally have noncarbon atoms (heteroatoms) as part of the main backbone chain. Examples are shown in Fig. 3.30. 

The functionality of the monomers must be at least two to form a polymer. If the functionality is two, a linear polymer will result. For a cross-linked polymer, the functionality must be three or more. 

The reaction between a dialcohol and a diacid, for example, proceeds as shown in Fig. 3.32, with subsequent reactions analogous to Step 2, combining intermediate esters of varying sizes to produce a polyester. 

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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-... 

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. 

It is the third of these criteria that offers the most powerful insight into the nature of the polymerization process for this important class of materials. We shall frequently use the terms step-growth and condensation polymers as synonyms, although by the end of the chapter it will be apparent that step-growth polymerization encompasses a wider range of reactions and products than either criteria (1) or (2) above would indicate. 

Condensation polymers are often formed from two distinct monomers, each of which is difunctional. The monomers have the forms AMA and BNB where A and B are functional groups that react to couple the M and N units and form a condensation by-product, AB. M and N are the mer units that form the polymer chain. The first step in the polymerization forms dimer ... 

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. 

The step-growth polymerization of ABx-monomers is by far the most intensively studied synthetic pathway to hyperbranched polymers. A number of AB2-monomers, suitable for step-growth polymerizations, are commercially available. This has, of course, initiated substantial activity in hyperbranched condensation polymers and a wide variety of examples have been reported in the literature [4],... 

This section introduces simple polymer reaction chemistry used to produce many commodity polymers. Understanding this simplified approach to the chemistry of polymer production Is Important In troubleshooting many extrusion processes, especially those that are producing unwanted degradation products that contaminate the discharge resin. There are two general types of polymer production processes 1) step or condensation reactions, and 2) addition or vinyl polymerization reactions. An overview of the reaction mechanisms wifi be presented in the next sections. 

In far too many instances trade-name polymer nomenclature conveys very little meaning regarding the structure of a polymer. Many condensation polymers, in fact, seem not to have names. Thus the polymer obtained by the step polymerization of formaldehyde and phenol is variously referred to a phenol-formaldehyde polymer, phenol-formaldehyde resin, phenolic, phenolic resin, and phenoplast. Polymers of formaldehyde or other aldehydes with urea or melamine are generally referred to as amino resins or aminoplasts without any more specific names. It is often extremely difficult to determine which aldehyde and which amino monomers have been used to synthesize a particular polymer being referred to as an amino resin. More specific nomenclature, if it can be called that, is afforded by indicating the two reactants as in names such as urea-formaldehyde resin or melamine-formaldehyde resin. 

Many of the common condensation polymers are listed in Table 1-1. In all instances the polymerization reactions shown are those proceeding by the step polymerization mechanism. This chapter will consider the characteristics of step polymerization in detail. The synthesis of condensation polymers by ring-opening polymerization will be subsequently treated in Chap. 7. A number of different chemical reactions may be used to synthesize polymeric materials by step polymerization. These include esterification, amidation, the formation of urethanes, aromatic substitution, and others. Polymerization usually proceeds by the reactions between two different functional groups, for example, hydroxyl and carboxyl groups, or isocyanate and hydroxyl groups. 

Although step polymerization of e-aminocaproic acid with itself is only a minor contribution to the overall conversion of lactam to polymer, it does determine the final degree of polymerization at equilibrium since the polymer undergoes self-condensation. The final... 

The demethanative coupling appears to be a step polymerization, as initial consumption of the germane monomer produces oligogermanes within the first few minutes, followed by further condensation to high polymer within hours at 25°C. Molecular weights of the permethylpolyger-mane (GPC, polystyrene calibration) range from Mn 1-4 X 104 and... 

An interesting thing is that the polyether with low polydispersity from chain-growth condensation polymerization possessed higher crystallinity than the one with broad molecular weight distribution from conventional step-growth condensation polymerization. The XRD pattern of the former polymer showed a stronger intensity, and the DSC profile showed the... 

Fig. 13.42 Simulation results of the RIM process involving a linear step polymerization T0 = Tw = 60°C, kf— 0.5L/moles, t(lii = 2.4 s. (a) Conversion contours at the time of fill, (h) Temperature contours at the time of fill. [Reprinted hy permission from J. D. Domine and C. G. Gogos, Computer Simulations of Injection Molding of a Reactive Linear Condensation Polymer, paper presented at the Society of Plastics Engineers, 34th Armu. Tech. Conf, Atlantic City, NJ, 1976. (Also published in the Polym. Eng. Sci., 20, 847-858 (1980) volume honoring Prof. B. Maxwell).]...

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