Condensation polymerization reactive functional groups

Besides addition polymerization, the other general way to prepare polymers is known as condensation polymerization or step growth polymerization. Much of the pioneering work on condensation polymerization was conducted by Wallace Carothers while he was employed by DuPont. He recognized that many natural polymers are formed from monomers with two reactive functional groups. For example, proteins are polymers of amino acids, which contain both amine and carboxylic acid groups. The formation of amide bonds is used to connect one monomer to another. Carothers s attempts to imitate nature led to a whole industry based on condensation polymerization. 

The general types of step-growth polymerizations are shown in Eigure 5.21. Since the resulting polymers contain reactive functional groups on either/both ends, it is referred to as a telechelic macromolecule. Although water is typically released as a byproduct of these polymerizations, other small molecules such as alcohols and alkyl halides may also be generated based on the monomers that co-condense. In its most simplest form, condensation reactions result in linear polymers from the reaction of... 

To construct a polymer, very many monomers must add to a growing polymer molecule, and the reaction must not falter after the first few molecules have reacted. This is achieved by having the polymer molecule retain highly reactive functional groups at all times during its synthesis. The two major types of polymer growth are addition polymerization and condensation polymerization. 

Step-growth polymerizations generally involve either one or more types of monomers. In either ease, each monomer has at least two reactive (functional) groups. In cases where only one type of monomer is involved, which is known as A-B step-growth polymerization, the functional groups on the monomer are different and capable of intramolecular reactions. An example is the formation of an aliphatic polyester by the self-condensation of co-hydroxycaproic acid (Equation 2.24). 

Condensation polymerization or step-growth polymerization is a process by which two molecules join together, resulting in loss of small molecules, which are often water. The type of end product resulting from a condensation polymerization is dependent on the type of reactive functional groups at the monomeric end, such as -OH, -COOH, -COOR, -COCl, -NH2, -CHO, and -NCO. The reaction is usually a non-catalyzed chemical condensation reaction and continues until the entire... 

Although the properties of condensation polymers are often superior to those exhibited by vinyl addition polymerization, little attention has been directed toward the introduction of fnnctional groups by polycondensation using appropriately substituted monomer. Polycondensation polymers may contain the reactive functional groups as a part of the polymer backbone or as pendent substituents. 

Molecules of a difiinctional monomer such as X-R-Y (where X and Y are mutually reactive functional groups) are polymerized via the elimination of small molecule by-products of XY, a linear condensation polymer with a general formula of X-(-R-)w-Y is formed, whereas when molecules of an olefinic monomer such as H2C=CHR are polymerized, a vinyl polymer with a structure of -[-H2C-CH(R)-]w- is produced. The difunctional and olefinic monomers have been the major monomer sources, and their step and chain polymerization reactions have been the main synthetic routes to the conventional polymers such as polyester and polystyrene, respectively [27]. 

Step polymerizations involve successive reactions between pairs of mutually-reactive functional groups which initially are provided by the monomer(s). The number of functional groups present on a molecule of monomer (i.e. its functionality) is of crucial importance, as can be appreciated by considering the formation of ester linkages from the condensation reaction of carboxylic acid groups with hydroxyl groups. Acetic acid and ethyl alcohol are monofunctional compounds which upon reaction together yield ethyl acetate with elimination of water... 

Schematic representation of synthetic approaches to produce a side-chain liquid crystal polymer. One strategy involves the polymerization of a substituted monomer using condensation polymerization (approach A) or addition (approach B) whereas its alternative is via the attachment of the mesogenic unit onto a preformed polymer (approach C). X and Y are mutually reactive functional groups.

The combined results of kinetic studies on condensation polymerization reactions and on the degradation of various polymers by reactions which bring about chain scission demonstrate quite clearly that the chemical reactivity of a functional group does not ordinarily depend on the size of the molecule to which it is attached. Exceptions occur only when the chain is so short as to allow the specific effect of one end group on the reactivity of the other to be appreciable. Evidence from a third type of polymer reaction, namely, that in which the lateral substituents of the polymer chain undergo reaction without alteration in the degree of polymerization, also support this conclusion. The velocity of saponification of polyvinyl acetate, for example, is very nearly the same as that for ethyl acetate under the same conditions. ... 

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