Monomers Small molecules from which

Mond process The purification of nickel by the formation and decomposition of nickel carbonyl, monomer A small molecule from which a polymer is formed. Examples CH2=CH2 for polyethylene NH2(CH2)6NH2 for nylon, monoprotic acid A Bronsted acid with one acidic hydrogen atom. Example CH COOI I. monosaccharide An individual unit from which carbohydrates are considered to be composed. Example C6H(206, glucose, multiple bond A double or triple bond between two atoms. 

If two identical molecules combine chemically a dimer is obtained. Acetylene for instance, is dimerised to vinylacetylene. If smaller molecules of a substance unite then a large molecule, a polymer, of high Molecular weight is obtained. The individual small molecule from which a polymer is formed is called a monomer. The chemical process for the formation, of a polymer is called polymerisation. This is exemplified in the following equation. 

Monomers The small molecules from which polymers are formed. 

These long molecules are composed of structural entities eaUed repeat units, which are successively repeated along the chain. The term monomer refers to the small molecule from which a polymer is synthesized. Hence, monomer and repeat unit mean different things, but sometimes the term monomer or monomer unit is used instead of the more proper term repeat unit. 

Polymers are relatively easy to manufacture. They usually can be synthesized in one step in which the major reactant is a substance consisting of small, simple organic molecules called monomers. A monomer is a molecule from which a polymer is made. 

A polymer is a large molecule, usually with a high molecular weight, built up from small repeating units. The simple molecule from which these repeating units are derived is called a monomer, and the process of converting a monomer to a polymer is called polymerization. 

Polymers are macromolecules characterized by high relative molecular mass and formed by linking large numbers of small molecules together. They essentially consist of repeating chemical units which are held by covalent bonds and derived, actually or conceptually, from molecules of low relative molecular mass called monomers. Thus, the term monomer refers to the small starting molecule from which a polymer is constructed and has not to be confused with the repeat unit. This last one represents, indeed, the basic structural unit whose repetition would produce the complete polymeric chain, except for the end-groups. 

Equation (5.6.8) represents a very important result in that it has an extra, non-negligible term, ASp/R, which is not present in the corresponding reaction of small molecules. From this equation, we can find the equilibrium monomer concentration at the temperature at which the polymerization is being carried out. It turns out that the equilibrium concentration of monomer is very low at normal temperatures of polymerization that are far below T. For example, for styrene at 60° C, [M]g is obtained using values of AHp and ASp foxmd in Ref. 4 (for hquid styrene and solid amorphous polystyrene) as... 

The polymer repeat unit arises from reacting together two different functional groups which usually originate on different monomers. In this case the repeat unit is different from either of the monomers. In addition, small molecules are often eliminated during the condensation reaction. Note the words usual and often in the previous statements exceptions to both statements are easily found. 

Fibrin is an elastic filamentous protein elaborated from its precursor, fibrinogen, which is present in plasma at high concentration. Fibrin is formed in response to the actions of thrombin. Thrombin cleaves small peptides from the fibrinogen molecule, forming fibrin monomers that will begin to polymerize and become crosslinked. 

The small molecules used as the basic building blocks for these large molecules are known as monomers. For example the commercially important material poly(vinyl chloride) is made from the monomer vinyl chloride. The repeat unit in the polymer usually corresponds to the monomer from which the polymer was made. There are exceptions to this, though. Poly(vinyl alcohol) is formally considered to be made up of vinyl alcohol (CH2CHOH) repeat units but there is, in fact, no such monomer as vinyl alcohol. The appropriate molecular unit exists in the alternative tautomeric form, ethanal CH3CHO. To make this polymer, it is necessary first to prepare poly(vinyl ethanoate) from the monomer vinyl ethanoate, and then to hydrolyse the product to yield the polymeric alcohol. 

Another classification system, first suggested by Carothers in 1929, is based on the nature of the chemical reactions employed in the polymerisation. Here the two major groups are the condensation and the addition polymers. Condensation polymers are those prepared from monomers where reaction is accompanied by the loss of a small molecule, usually of water, for example polyesters which are formed by the condensation shown in Reaction 1.1. 

The activity of PK and NRPSs is often precluded and/or followed by actions upon the natural products by modifying enzymes. There exists a first level of diversity in which the monomers for respective synthases must be created. For instance, in the case of many NRPs, noncanonical amino acids must be biosynthesized by a series of enzymes found within the biosynthetic gene cluster in order for the peptides to be available for elongation by the NRPS. A second level of molecular diversity comes into play via post-synthase modification. Examples of these activities include macrocyclization, heterocyclization, aromatization, methylation, oxidation, reduction, halogenation, and glycosylation. Finally, a third level of diversity can occur in which molecules from disparate secondary metabolic pathways may interact, such as the modification of a natural product by an isoprenoid oligomer. Here, we will cover only a small subsection of... 

A chemical reaction by which small molecules (of monomer) are joined together to form large molecules (of polymer). Polymerisation may be effected by (a) addition, in which the polymer molecule is a multiple of the monomer molecule, (b) by condensation, in which the empirical formula of the polymer differs from that of the monomer, and (c) by copolymerisation, in which the polymer molecule is built up from two or more different monomers... 

Polymers were originally classified by Carothers [1929] into condensation and addition polymers on the basis of the compositional difference between the polymer and the monomer(s) from which it was synthesized. Condensation polymers were those polymers that were formed from polyfunctional monomers by the various condensation reactions of organic chemistry with the elimination of some small molecule such as water. An example of such a condensation polymer is the polyamides formed from diamines and diacids with the elimination of water according to... 

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