Polymerization The combination of many

Polymerization The combination of many small molecules (monomers) to form large molecules (polymers). 

Polymers are substances whose molecules are very large, formed by the combination of many small and simpler molecules usually referred to as monomers. The chemical reaction by which single and relatively small monomers react with each other to form polymers is known as polymerization (Young and Lovell 1991). Polymers may be of natural origin or, since the twentieth century, synthesized by humans. Natural polymers, usually referred to as biopolymers, are made by living organisms. Common examples of biopolymers are cellulose, a carbohydrate made only by plants (see Textbox 53) collagen, a protein made solely by animals (see Textbox 61), and the nucleic acid DNA, which is made by both plants and animals (see Textbox 64). 

Polyethylene (Section 6 21) A polymer of ethylene Polymer (Section 6 21) Large molecule formed by the repeti tive combination of many smaller molecules (monomers) Polymerase chain reaction (Section 28 16) A laboratory method for making multiple copies of DNA Polymerization (Section 6 21) Process by which a polymer is prepared The principal processes include free radical cationic coordination and condensation polymerization Polypeptide (Section 27 1) A polymer made up of many (more than eight to ten) amino acid residues Polypropylene (Section 6 21) A polymer of propene Polysaccharide (Sections 25 1 and 25 15) A carbohydrate that yields many monosacchande units on hydrolysis Potential energy (Section 2 18) The energy a system has ex elusive of Its kinetic energy... 

Under certain condition, however, reactions are still preferably conducted in solution. This is the case e.g., for heterogeneous reactions and for conversions, which deliver complex product mixtures. In the latter case, further conversion of this mixture on the solid support is not desirable. In these instances, the combination of solution chemistry with polymer-assisted conversions can be an advantageous solution. Polymer-assisted synthesis in solution employs the polymer matrix either as a scavenger or for polymeric reagents. In both cases the virtues of solution phase and solid supported chemistry are ideally combined allowing for the preparation of pure products by filtration of the reactive resin. If several reactive polymers are used sequentially, multi-step syntheses can be conducted in a polymer-supported manner in solution as well. As a further advantage, many reactive polymers can be recycled for multiple use. 

The fluidity is one of the most vital properties of biological membranes. It relates to many functions involved in biological system, and effective biomembrane mimetic chemistry depends on the combination of both stability and mobility of the model membranes. However, in the polymerized vesicles the polymer chain interferes with the motion of the side groups and usually causes a decrease or even the loss of the fluid phases inside the polymerized vesicle (72,13). 

True self-assembly is observed in the formation of many oligomeric proteins. Indeed, Friedman and Beychok reviewed efforts to define the subunit assembly and reconstitution pathways in multisubunit proteins, and all of the several dozen examples cited in their review represent true self-assembly. Polymeric species are also formed by true self-assembly, and the G-actin to F-actin transition is an excellent example. By contrast, there are strong indications that ribosomal RNA species play a central role in specifying the pathway to and the structure of ribosome particles. And it is interesting to note that the assembly of the tobacco mosaic virus (TMV) appears to be a two-step hybrid mechanism the coat protein subunits first combine to form 34-subunit disks by true self-assembly from monomeric and trimeric com-... 

There are numerous reports available on the optimization of reaction conditions of 2-oxazolines. For instance, the effect of solvent, temperature, pressure, monomer to initiator ratio, and many other critical parameters have been investigated to obtain the optimum conditions [64-68]. Besides these parameters, the initiator structure has also a great effect on the polymerization. The investigation on different initiator structures provided the necessary kinetic parameters for the use of functional initiators [69]. Heterofunctional initiators have been used in polymer science for the combination of different types of monomers that can be polymerized with different polymerization techniques, such as ATRP and CROP [70-72]. 

The polymerization systems discussed in this article are those in which polymerizing monomer is directly involved in the electron transferring pair, which enables the production of ion-radical on monomer. At the moment we are able to induce photosensitized ionic polymerization only in limited instances. When the charge transfer polymerization is discussed, strict distinction between radical and ionic mechanisms is impossible. As shown in Fig. 2, the difference between ion and radical and that between molecule and ion-radical is only a matter of one electron. Thermal electron transfer polymerization is demonstrated for many polymerization systems. The combination of photochemistry and electron transfer polymerization is very promising and may open up a new field in photopolymers. 

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