Polymeric condensation, additive

Gas-phase polymerization of propylene was pioneered by BASF, who developed the Novolen process which uses stirred-bed reactors (Fig. 8) (125). Unreacted monomer is condensed and recycled to the polymerizer, providing additional removal of the heat of reaction. As in the early Hquid-phase systems, post-reactor treatment of the polymer is required to remove catalyst residues (126). The high content of atactic polymer in the final product limits its usefiilness in many markets. 

Process in wliich the addition of heat, catalyst or both, with or without pressure, causes the physical properties of the plastic to change through a chemical reaction. Reaction may be condensation, polymerization or addition reactions. 

Though less prevalent than addition polymerization, condensation polymerization produces important polymers such as polyesters, polyamides (nylons), polycarbonates, polyurethanes, and phenol-formaldehyde resins (Chapter 12). 

How would you explain to a young science student how to decide whether a given compound might be useful as a monomer for addition polymerization Condensation polymerization ... 

In step growth polymerization, initially dimer formation takes place due to condensation, addition or ring opening etc., e.g. 

Figure 1. The synthesis of sequential IPN above and simultaneous interpenetrating networks, SIN, below. For the synthesis of SIN, two different reactions operate simultaneously such as condensation polymerization and addition polymerization. Reproduced with permission from Ref. 23. Copyright 1981, Plenum Publishing.

Typically chain polymerizations form addition polymers and stepwise polymerizations form condensation polymerizations. 

In general, there are two distinctively different classes of polymerization (a) addition or chain growth polymerization and (b) condensation or step growth polymerization. In the former, the polymers are synthesized by the addition of one unsaturated unit to another, resulting in the loss of multiple bonds. Some examples of addition polymers are (a) poly(ethylene), (b) poly(vinyl chloride), (c) poly(methyl methacrylate), and (d) poly(butadiene). The polymerization is initiated by a free radical, which is generated from one of several easily decomposed compounds. Examples of free radical initiators include (a) benzoyl peroxide, (b) di-tert-butyl peroxide, and (c) azobiisobutyronitrile. 

Polymers usually are prepared by two different types of polymerization reactions — addition and condensation. In addition polymerization all of the atoms of the monomer molecules become part of the polymer in condensation polymerization some of the atoms of the monomer are split off in the reaction as water, alcohol, ammonia, or carbon dioxide, and so on. Some polymers can be formed either by addition or condensation reactions. An example is polyethylene glycol, which, in principle, can form either by dehydration of 1,2-ethanediol (ethylene glycol), which is condensation, or by addition polymerization of oxacyclopropane (ethylene oxide) 1... 

The synthesis of optically active polymers is an important area in macromolecular science, as they have a wide variety of potential applications, including the preparation of CSPs [31-37]. Many of the optically active polymers with or without binding to silica gel were used as CSPs and commercialized [38]. These synthetic polymers are classified into three groups according to the methods of polymerization (1) addition polymers, including vinyl, aldehyde, isocyanide, and acetylene polymers, (2) condensation polymers consisting of polyamides and polyurethanes, and (3) cross-linked gels (template polymerization). The art of the chiral resolution on these polymer-based CSPs is described herein. 

Cure — A process of changing the properties of a polymer by a chemical reaction (condensation, polymerization, or addition). In elastomers it means mainly cross-linking or vulcanization. 

Polymers are made from the repeating units through two process. One process simply adds each succeeding monomer onto the chain through various methods, called addition polymerization. Condensation polymerization is the second process of adding monomers onto the chain to make large molecules. In condensation polymerization, small molecules like water are removed as the monomer unit is added onto the chain. 

The reactions described so far are examples of condensation polymerization. In such reactions, small molecules (in these cases, water molecules) are eliminated from the reacting functional groups. Another type of polymerization is addition polymerization, illustrated by the polymerization of ethylene ... 

Acetaldehyde is a highly reactive compound exhibiting the general reactivity7 of aldehydes (qv). Acetaldehyde undergoes numerous condensation, addition, and polymerization reactions under suitable conditions, the oxygen or any of the hydrogens can be replaced. 

More specifically, the acyclic alkenes is defined gation, condensation-type polymerization, where the term condensation-type arises from the liberation of a by-product that advances the reaction. The other possibility for step polymerization is addition-type, where the resulting polymer linkage is an adduct of the two monomers, and no atoms are lost (e g. polyurethanes). 

There is an alternative, somewhat less meaningful system of classification addition polymerization, in which molecules of monomer are simply added together and con-iensation polymerization, in which monomer molecules combine with loss of some simple nolecules like water. As it happens, the two systems almost exactly coincide nearly all ases of chain-reaction polymerization involve addition polymerization nearly all cases pf step-reaction polymerization involve condensation polymerization. Indeed, some hemists use the term addition polymerization to mean polymerization via chain reactions. 

Figure 1.18. Branching during step polymerization, (a) Addition of a trifunctional agent (e.g. a triol, BBB) to a self-condensing difunctional system (e.g. a hydroxy acid, BA), (b) Hyperbranching from a system AB2. In both cases A may react only with B.

There are two fundamental polymerization mechanisms. Classically, they have been differentiated as addition polymerization and condensation polymerization. In the addition process, no by-product is evolved, as in the polymerization of vinyl chloride (see below) whereas in the condensation process, just as in various condensation reactions (e.g., esterification, etherification, amidation, etc.) of organic chemistry, a low-molecular-weight by-product (e.g., H2O, HCl, etc.) is evolved. Polymers formed by addition polymerization do so by the successive addition of unsaturated monomer units in a chain reaction promoted by the active center. Therefore, addition polymerization is called chain polymerization. Similarly, condensation polymerization is referred to as step polymerization since the polymers in this case are formed by stepwise, intermolecular condensation of reactive groups. (The terms condensation and step are commonly used synonymously, as we shall do in this book, and so are the terms addition and chain. However, as it will be shown later in this section, these terms cannot always be used synonymously. In fact, the condensation-addition classification is primarily applicable to the composition or structure of polymers, whereas the step-chain classification applies to the mechanism of polymerization reactions.)... 

Thus, the polyesterification reaction mixture at any instance consists of various-sized diol, diacid, and hydroxyacid molecules. Any OH-containing molecule can react with any COOH-containing molecule. This is a general characteristic of step polymerization. A comparative account of the differences between step polymerization or condensation polymerization on the one hand and chain polymerization or addition polymerization (see Chapter 6) on the other hand is given in Table 5.1. 

A comparative account of the differences between step polymerization or condensation polymerization on the one hand and chain polymerization or addition polymerization (see Chapter 6) on the other hand is given in Table 5.1. 

Iv) Substitution. The skeleton of an oligomeric or polymeric system is constructed by condensation, addition or ring-opening techniques, but variations in side-group structure must generally be introduced by substitutive methods ... 

The Commission on Macromolecular Nomenclature defined 52 terms related to polymer structure, including polymer, constitutional units, monomer, polymerization, regular polymer, tactic polymer, block polymer, graft polymer, monomeric unit, degree of polymerization, addition polymerization, condensation polymerization, homopolymer. 

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